Xenobiology (XB) is a subfield of synthetic biology, the study of synthesizing and manipulating biological devices and systems. The name "xenobiology" derives from the Greek word xenos,
which means "stranger, alien". Xenobiology is a form of biology that is
not (yet) familiar to science and is not found in nature. In practice, it describes novel biological systems and biochemistries that differ from the canonical DNA–RNA-20 amino acid system (see central dogma of molecular biology). For example, instead of DNA or RNA, XB explores nucleic acid analogues, termed xeno nucleic acid (XNA) as information carriers. It also focuses on an expanded genetic code and the incorporation of non-proteinogenic amino acids, or "xeno amino acids" into proteins.
Difference between xeno-, exo-, and astro-biology
"Astro" means "star" and "exo" means "outside". Both exo- and astrobiology deal with the search for naturally evolved life in the Universe, mostly on other planets in the circumstellar habitable zone. (These are also occasionally referred to as xenobiology.)
Whereas astrobiologists are concerned with the detection and analysis
of life elsewhere in the Universe, xenobiology attempts to design forms
of life with a different biochemistry or different genetic code than on planet Earth.
Aims
Xenobiology has the potential to reveal fundamental knowledge about biology and the origin of life.
In order to better understand the origin of life, it is necessary to
know why life evolved seemingly via an early RNA world to the
DNA-RNA-protein system and its nearly universal genetic code. Was it an evolutionary "accident" or were there constraints that ruled
out other types of chemistries? By testing alternative biochemical
"primordial soups", it is expected to better understand the principles
that gave rise to life as we know it.
Xenobiology is an approach to develop industrial production systems
with novel capabilities by means of biopolymer engineering and pathogen
resistance. The genetic code encodes in all organisms 20 canonical amino
acids that are used for protein biosynthesis. In rare cases, special
amino acids such as selenocysteine or pyrrolysine can be incorporated by
the translational apparatus in to proteins of some organisms. Together, these 20+2 Amino Acids are known as the 22 Proteinogenic Amino Acids. By using additional amino acids from among the over 700 known to
biochemistry, the capabilities of proteins may be altered to give rise
to more efficient catalytical or material functions. The EC-funded
project Metacode, for example, aims to incorporate metathesis (a useful catalytical
function so far not known in living organisms) into bacterial cells.
Another reason why XB could improve production processes lies in the
possibility to reduce the risk of virus or bacteriophage contamination
in cultivations since XB cells would no longer provide suitable host
cells, rendering them more resistant (an approach called semantic
containment)
Xenobiology offers the option to design a "genetic firewall", a
novel biocontainment system, which may help to strengthen and diversify
current bio-containment approaches. One concern with traditional genetic engineering and biotechnology is horizontal gene transfer
to the environment and possible risks to human health. One major idea
in XB is to design alternative genetic codes and biochemistries so that
horizontal gene transfer is no longer possible. Additionally alternative biochemistry also allows for new synthetic
auxotrophies. The idea is to create an orthogonal biological system that
would be incompatible with natural genetic systems.
Scientific approach
In
xenobiology, the aim is to design and construct biological systems that
differ from their natural counterparts on one or more fundamental
levels. Ideally these new-to-nature organisms would be different in
every possible biochemical aspect exhibiting a very different genetic
code. The long-term goal is to construct a cell that would store its genetic
information not in DNA but in an alternative informational polymer
consisting of xeno nucleic acids (XNA), different base pairs, using
non-canonical amino acids and an altered genetic code. So far cells have
been constructed that incorporate only one or two of these features.
Originally this research on alternative forms of DNA was driven by
the question of how life evolved on earth and why RNA and DNA were
selected by (chemical) evolution over other possible nucleic acid
structures. Two hypotheses for the selection of RNA and DNA as life's backbone are
either they are favored under life on Earth's conditions, or they were
coincidentally present in pre-life chemistry and continue to be used
now. Systematic experimental studies aiming at the diversification of the
chemical structure of nucleic acids have resulted in completely novel
informational biopolymers. So far a number of XNAs with new chemical
backbones or leaving group of the DNA have been synthesized e.g.: hexose nucleic acid (HNA); threose nucleic acid (TNA), glycol nucleic acid (GNA) cyclohexenyl nucleic acid (CeNA). The incorporation of XNA in a plasmid, involving 3 HNA codons, has been accomplished already in 2003. This XNA is used in vivo (E coli) as template for DNA synthesis. This
study, using a binary (G/T) genetic cassette and two non-DNA bases
(Hx/U), was extended to CeNA, while GNA seems to be too alien at this
moment for the natural biological system to be used as template for DNA
synthesis. Extended bases using a natural DNA backbone could, likewise, be
transliterated into natural DNA, although to a more limited extent.
Aside being used as extensions to template DNA strands, XNA activity has been tested for use as genetic catalysts. Although proteins are the most common components of cellular enzymatic activity,
nucleic acids are also used in the cell to catalyze reactions. A 2015
study found several different kinds of XNA, most notably FANA
(2'-fluoroarabino nucleic acids), as well as HNA, CeNA and ANA (arabino
nucleic acids) could be used to cleave RNA during post-transcriptional RNA processing acting as XNA enzymes, hence the name XNAzymes. FANA XNAzymes also showed the ability to ligate DNA, RNA and XNA substrates. Although XNAzyme studies are still preliminary, this study was a step in the direction of searching for synthetic circuit components
that are more efficient than those containing DNA and RNA counterparts
that can regulate DNA, RNA, and their own, XNA, substrates.
While XNAs have modified backbones, other experiments target the
replacement or enlargement of the genetic alphabet of DNA with unnatural
base pairs. For example, DNA has been designed that has – instead of
the four standard bases A, T, G, and C – six bases A, T, G, C, and the
two new ones P and Z (where Z stands for
6-Amino-5-nitro3-(l'-p-D-2'-deoxyribofuranosyl)-2(1H)-pyridone, and P
stands for
2-Amino-8-(1-beta-D-2'-deoxyribofuranosyl)imidazo[1,2-a]-1,3,5-triazin-4
(8H)). In a systematic study, Leconte et al. tested the viability of 60
candidate bases (yielding potentially 3600 base pairs) for possible
incorporation in the DNA.
In 2002, Hirao et al. developed an unnatural base pair between
2-amino-8-(2-thienyl)purine (s) and pyridine-2-one (y) that functions in vitro in transcription and translation toward a genetic code for protein synthesis containing a non-standard amino acid. In 2006, they created 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds) and
pyrrole-2-carbaldehyde (Pa) as a third base pair for replication and
transcription, and afterward, Ds and
4-[3-(6-aminohexanamido)-1-propynyl]-2-nitropyrrole (Px) was discovered
as a high fidelity pair in PCR amplification. In 2013, they applied the Ds-Px pair to DNA aptamer generation by in vitro
selection (SELEX) and demonstrated the genetic alphabet expansion
significantly augment DNA aptamer affinities to target proteins.
In May 2014, researchers announced that they had successfully introduced two new artificial nucleotides
into bacterial DNA, alongside the four naturally occurring nucleotides,
and by including individual artificial nucleotides in the culture
media, were able to passage the bacteria 24 times; they did not create
mRNA or proteins able to use the artificial nucleotides.
Novel polymerases
Neither the XNA nor the unnatural bases are recognized by natural polymerases.
One of the major challenges is to find or create novel types of
polymerases that will be able to replicate these new-to-nature
constructs. In one case a modified variant of the HIV-reverse transcriptase was found to be able to PCR-amplify an oligonucleotide containing a third type base pair. Pinheiro et al. (2012) demonstrated that the method of polymerase
evolution and design successfully led to the storage and recovery of
genetic information (of less than 100bp length) from six alternative
genetic polymers based on simple nucleic acid architectures not found in
nature, xeno nucleic acids.
Genetic code engineering
One of the goals of xenobiology is to rewrite the genetic code. The most promising approach to change the code is the reassignment of seldom used or even unused codons. In an ideal scenario, the genetic code is expanded by one codon, thus
having been liberated from its old function and fully reassigned to a
non-canonical amino acid (ncAA) ("code expansion"). As these methods
are laborious to implement, and some short cuts can be applied ("code
engineering"), for example in bacteria that are auxotrophic for specific
amino acids and at some point in the experiment are fed isostructural
analogues instead of the canonical amino acids for which they are
auxotrophic. In that situation, the canonical amino acid residues in
native proteins are substituted with the ncAAs. Even the insertion of
multiple different ncAAs into the same protein is possible. Finally, the repertoire of 20 canonical amino acids can not only be expanded, but also reduced to 19. By reassigning transfer RNA (tRNA)/aminoacyl-tRNA synthetase pairs the
codon specificity can be changed. Cells endowed with such
aminoacyl-[tRNA synthetases] are thus able to read [mRNA] sequences that
make no sense to the existing gene expression machinery. Altering the codon: tRNA synthetases pairs may lead to the in vivo
incorporation of the non-canonical amino acids into proteins. In the past reassigning codons was mainly done on a limited scale. In
2013, however, Farren Isaacs and George Church at Harvard University
reported the replacement of all 321 TAG stop codons present in the
genome of E. coli
with synonymous TAA codons, thereby demonstrating that massive
substitutions can be combined into higher-order strains without lethal
effects. Following the success of this genome wide codon replacement, the
authors continued and achieved the reprogramming of 13 codons throughout
the genome, directly affecting 42 essential genes.
An even more radical change in the genetic code is the change of a
triplet codon to a quadruplet and even quintuplet codon pioneered by
Sisido in cell-free systems and by Schultz in bacteria. Finally, non-natural base pairs can be used to introduce novel amino acid in proteins.
The goal of substituting DNA by XNA may also be reached by another
route, namely by engineering the environment instead of the genetic
modules. This approach has been successfully demonstrated by Marlière
and Mutzel with the production of an E. coli strain whose DNA is
composed of standard A, C and G nucleotides but has the synthetic
thymine analogue 5-chlorouracil instead of thymine (T) in the
corresponding positions of the sequence. These cells are then dependent
on externally supplied 5-chlorouracil for growth, but otherwise they
look and behave as normal E. coli. These cells, however, are
currently not yet fully auxotrophic for the Xeno-base since they are
still growing on thymine when this is supplied to the medium.
Biosafety
Xenobiological
systems are designed to convey orthogonality to natural biological
systems. A (still hypothetical) organism that uses XNA, different base pairs and polymerases and has an altered genetic code
will hardly be able to interact with natural forms of life on the
genetic level. Thus, these xenobiological organisms represent a genetic
enclave that cannot exchange information with natural cells. Altering the genetic machinery of the cell leads to semantic
containment. In analogy to information processing in IT, this safety
concept is termed a "genetic firewall". The concept of the genetic firewall seems to overcome a number of limitations of previous safety systems. A first experimental evidence of the theoretical concept of the genetic
firewall was achieved in 2013 with the construction of a genomically
recoded organism (GRO). In this GRO all known UAG stop codons in E.coli
were replaced by UAA codons, which allowed for the deletion of release
factor 1 and reassignment of UAG translation function. The GRO exhibited
increased resistance to T7 bacteriophage, thus showing that alternative
genetic codes do reduce genetic compatibility. This GRO, however, is still very similar to its natural "parent" and
cannot be regarded to have a genetic firewall. The possibility of
reassigning the function of large number of triplets opens the
perspective to have strains that combine XNA, novel base pairs, new
genetic codes, etc. that cannot exchange any information with the
natural biological world.
Regardless of changes leading to a semantic containment mechanism in new
organisms, any novel biochemical systems still has to undergo a
toxicological screening. XNA, novel proteins, etc. might represent novel
toxins, or have an allergic potential that needs to be assessed.
Governance and regulatory issues
Xenobiology
might challenge the regulatory framework, as currently laws and
directives deal with genetically modified organisms and do not directly
mention chemically or genomically modified organisms. Taking into
account that real xenobiology organisms are not expected in the next few
years, policy makers do have some time at hand to prepare themselves
for an upcoming governance challenge. Since 2012, the following groups
have picked up the topic as a developing governance issue: policy
advisers in the US, four National Biosafety Boards in Europe, the European Molecular Biology Organisation, and the European Commission's Scientific Committee on Emerging and
Newly Identified Health Risks (SCENIHR) in three opinions (Definition, risk assessment methodologies and safety aspects, and risks to the environment and biodiversity related to synthetic
biology and research priorities in the field of synthetic biology.)
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics
that are analogous to the glass lenses of an optical light microscope
to control the electron beam, for instance focusing it to produce
magnified images or electron diffraction
patterns. As the wavelength of an electron can be up to 100,000 times
smaller than that of visible light, electron microscopes have a much
higher resolution of about 0.1 nm, which compares to about 200 nm for light microscopes. Electron microscope may refer to:
Additional details can be found in the above links. This article
contains some general information mainly about transmission and scanning
electron microscopes.
Many developments laid the groundwork of the electron optics used in microscopes. One significant step was the work of Hertz in 1883 who made a cathode-ray tube with electrostatic and magnetic deflection,
demonstrating manipulation of the direction of an electron beam. Others
were focusing of the electrons by an axial magnetic field by Emil Wiechert in 1899, improved oxide-coated cathodes which produced more electrons by Arthur Wehnelt in 1905 and the development of the electromagnetic lens in 1926 by Hans Busch. According to Dennis Gabor, the physicist Leó Szilárd tried in 1928 to convince him to build an electron microscope, for which Szilárd had filed a patent.
Reproduction of an early electron microscope constructed by Ernst Ruska in the 1930s
To this day the issue of who invented the transmission electron microscope is controversial. In 1928, at the Technische Hochschule in Charlottenburg (now Technische Universität Berlin), Adolf Matthias (Professor of High Voltage Technology and Electrical Installations) appointed Max Knoll
to lead a team of researchers to advance research on electron beams and
cathode-ray oscilloscopes. The team consisted of several PhD students
including Ernst Ruska. In 1931, Max Knoll and Ernst Ruska successfully generated magnified images of mesh grids placed over an
anode aperture. The device, a replicate of which is shown in the figure,
used two magnetic lenses to achieve higher magnifications, the first
electron microscope. (Max Knoll died in 1969, so did not receive a share
of the 1986 Nobel prize for the invention of electron microscopes.)
Apparently independent of this effort was work at Siemens-Schuckert by Reinhold Rüdenberg. According to patent law (U.S. Patent No. 2058914 and 2070318, both filed in 1932), he is the inventor of the electron microscope, but
it is not clear when he had a working instrument. He stated in a very
brief article in 1932 that Siemens had been working on this for some years before the patents
were filed in 1932, claiming that his effort was parallel to the
university development. He died in 1961, so similar to Max Knoll, was
not eligible for a share of the 1986 Nobel prize.
In the following year, 1933, Ruska and Knoll built the first
electron microscope that exceeded the resolution of an optical (light)
microscope. Four years later, in 1937, Siemens financed the work of Ernst Ruska and Bodo von Borries, and employed Helmut Ruska, Ernst's brother, to develop applications for the microscope, especially with biological specimens. Also in 1937, Manfred von Ardenne pioneered the scanning electron microscope. Siemens produced the first commercial electron microscope in 1938. The first North American electron microscopes were constructed in the 1930s, at the Washington State University by Anderson and Fitzsimmons and at the University of Toronto by Eli Franklin Burton and students Cecil Hall, James Hillier, and Albert Prebus. Siemens produced a transmission electron microscope (TEM) in 1939. Although current transmission electron microscopes are capable of two
million times magnification, as scientific instruments they remain
similar but with improved optics.
In the 1940s, high-resolution electron microscopes were developed, enabling greater magnification and resolution. By 1965, Albert Crewe at the University of Chicago introduced the scanning transmission electron microscope using a field emission source, enabling scanning microscopes at high resolution. By the early 1980s improvements in mechanical stability as well as the
use of higher accelerating voltages enabled imaging of materials at the
atomic scale. In the 1980s, the field emission gun
became common for electron microscopes, improving the image quality due
to the additional coherence and lower chromatic aberrations. The 2000s
were marked by advancements in aberration-corrected electron microscopy,
allowing for significant improvements in resolution and clarity of
images.
The original form of the electron microscope, the transmission electron microscope (TEM), uses a high voltageelectron beam to illuminate the specimen and create an image. An electron beam is produced by an electron gun, with the electrons typically having energies in the range 20 to 400 keV, focused by electromagnetic
lenses, and transmitted through a thin specimen. When it emerges from
the specimen, the electron beam carries information about the structure
of the specimen that is then magnified by the lenses of the microscope.
The spatial variation in this information (the "image") may be viewed by
projecting the magnified electron image onto a detector. For example, the image may be viewed directly by an operator using a fluorescent viewing screen coated with a phosphor or scintillator material such as zinc sulfide. More commonly a high-resolution phosphor is coupled by means of a lens optical system or a fibre optic light-guide to the sensor of a digital camera. A different approach is to use a direct electron detector which has no scintillator, which addresses some of the limitations of scintillator-coupled cameras.
For many years the resolution of TEMs was limited by aberrations of the electron optics, primarily the spherical aberration.
In most recent instruments hardware correctors can reduce spherical
aberration and other aberrations, improving the resolution in high-resolution transmission electron microscopy (HRTEM) to below 0.5 angstrom (50 picometres), enabling magnifications of more than 50 million times. The ability of HRTEM to determine the positions of atoms within materials is useful for many areas of research and development.
An SEM produces images by probing the specimen with a focused electron beam that is scanned across the specimen (raster scanning).
When the electron beam interacts with the specimen, it loses energy and
is scattered in different directions by a variety of mechanisms. These
interactions lead to, among other events, emission of low-energy secondary electrons and high-energy backscattered electrons, light emission (cathodoluminescence) or X-ray
emission. All of these signals carrying information about the specimen,
such as the surface topography and composition. The image displayed
when using an SEM shows the variation in the intensity of any of these
signals as an image. In these each position in the image corresponding
to a position of the beam on the specimen when the signal was generated.
TESCAN S8000X SEM
SEMs are different from TEMs in that they use electrons with much lower energy, generally below 20 keV, while TEMs generally use electrons with energies in the range of 80-300 keV. Thus, the electron sources and optics of the two microscopes have
different designs, and they are normally separate instruments.
A STEM combines features of both a TEM and a SEM by rastering a
focused incident probe across a specimen, but now mainly using the
electrons which are transmitted through the sample. Many types of
imaging are common to both TEM and STEM, but some such as annular dark-field imaging
and other analytical techniques are much easier to perform with higher
spatial resolutions in a STEM instrument. One drawback is that image
data is acquired in serial rather than in parallel fashion.
The
most common methods of obtaining images in an electron microscope
involve selecting different directions for the electrons that have been
transmitted through a sample, and/or electrons of different energies.
There are a very large number of methods of doing this, although not all
are very common.
Secondary electrons
Electron–matter interaction volume and types of signal generated in a SEM
In a SEM the signals result from interactions of the electron beam
with atoms within the sample. The most common mode is to use the secondary electrons (SE) to produce images. Secondary electrons have very low energies, on the order of 50 eV, which limits their mean free path in solid matter to a few nanometers below the sample surface. The electrons are detected by an Everhart–Thornley detector, which is a type of collector-scintillator-photomultiplier
system. The signal from secondary electrons tends to be highly
localized at the point of impact of the primary electron beam, making it
possible to collect images of the sample surface with a resolution of
better than 1 nm, and with specialized instruments at the atomic scale.
The brightness of the signal depends on the number of secondary electrons reaching the detector.
If the beam enters the sample perpendicular to the surface, then the
electrons come out symmetrically about the axis of the beam. As the
angle of incidence increases, the interaction volume from which they
cone increases and the "escape" distance from one side of the beam
decreases, resulting in more secondary electrons being emitted from the
sample. Thus steep surfaces and edges tend to be brighter than flat
surfaces, which results in images with a well-defined, three-dimensional
appearance that is similar to a reflected light image.
Backscattered electrons
Backscattered electrons (BSE) are those emitted back out from the
specimen due to beam-specimen interactions where the electrons undergo elastic and inelastic
scattering. They are conventionally defined as having energies from 50
eV up to the energy of the primary beam. Backscattered electrons can be
used for both imaging and to form an electron backscatter diffraction (EBSD) image, the latter can be used to determine the crystallography of the specimen.
Electron backscatter diffraction pattern for (001) single crystal silicon crystals taken at 20kV using Oxford S2 detector
Heavy elements (high atomic number) backscatter electrons more
strongly than light elements (low atomic number), and thus appear
brighter in the image, BSE images can therefore be used to detect areas
with different chemical compositions. To optimize the signal, dedicated backscattered electron detectors are
positioned above the sample in a "doughnut" type arrangement,
concentric with the electron beam, maximizing the solid angle of
collection. BSE detectors are usually either scintillator or
semiconductor types. When all parts of the detector are used to collect
electrons symmetrically about the beam, atomic number contrast is
produced. However, strong topographic contrast is produced by collecting
back-scattered electrons from one side above the specimen using an
asymmetrical, directional BSE detector; the resulting contrast appears
as if there was illumination of the topography from that side.
Semiconductor detectors can be made in radial segments that can be
switched in or out to control the type of contrast produced and its
directionality.
Diffraction contrast imaging
Diffraction
contrast uses the variation in either or both the direction of
diffracted electrons or their amplitude as a function of position as the
contrast mechanism. It is one of the simplest ways to image in a
transmission electron microscope, and widely used.
The idea is to use an objective aperture below the sample and
select only one or a range of different diffracted directions, then use
these to form an image. When the aperture includes the incident beam
direction the images are called bright field, since in the
absence of any sample the field of view would be uniformly bright. When
the aperture excludes the incident beam the images are called dark field, since similarly without a sample the image would be uniformly dark.One variant of this is called weak-beam dark-field microscopy, and can be used to obtain high resolution images of defects such as dislocations.
In high-resolution transmission electron microscopy (also sometimes
called high-resolution electron microscopy) a number of different
diffracted beams are allowed through the objective aperture. These
interfere, leading to images which represent the atomic structure of the
material. These can include the incident beam direction, or with
scanning transmission electron microscopes they typically are for a
range of diffracted beams excluding the incident beam. Depending upon how thick the samples are and the aberrations
of the microscope, these images can either be directly interpreted in
terms of the positions of columns of atoms, or require a more careful
analysis using calculations of the multiple scattering of the electrons and the effect of the contrast transfer function of the microscope.
There are many other imaging variants that can also to lead to atomic level information. Electron holography uses the interference of electrons which have been through the sample and a reference beam. 4D STEM collects diffraction data at each point using a scanning instrument, then processes them to produce different types of images.
EDS spectrum of the mineral crust of the vent shrimp Rimicaris exoculata Most of these peaks are K-alpha and K-beta lines. One peak is from the L shell of iron.
X-ray microanalysis is a method of obtaining local chemical
information within electron microscopes of all types, although it is
most commonly used in scanning instruments. When high energy electrons
interact with atoms they can knock out electrons, particularly those in
the inner shells and core electrons. These are then filled by valence electron, and the energy difference between the valence and core states can be converted into an x-ray
which is detected by a spectrometer. The energies of these x-rays is
somewhat specific to the atomic species, so local chemistry can be
probed.
Experimental electron energy loss spectrum, showing the major features: zero-loss peak, plasmon peaks and core loss edge.
Similar to X-ray microanalysis, the energies of electrons which have
transmitted through a sample can be analyzed and yield information
ranging from details of the local electronic structure to chemical
information.
Transmission electron microscopes can be used in electron diffraction mode where a map of the angles of the electrons leaving the sample is produced. The advantages of electron diffraction over X-ray crystallography
are primarily in the size of the crystals. In X-ray crystallography,
crystals are commonly visible by the naked eye and are generally in the
hundreds of micrometers in length. In comparison, crystals for electron
diffraction must be less than a few hundred nanometers in thickness, and
have no lower boundary of size. Additionally, electron diffraction is
done on a TEM, which can also be used to obtain other types of
information, rather than requiring a separate instrument.
There are many variants on electron diffraction, depending upon
exactly what type of illumination conditions are used. If a parallel
beam is used with an aperture to limit the region exposed to the
electrons then sharp diffraction features are normally observed, a
technique called selected area electron diffraction. This is often the main technique used. Another common approach uses conical illumination and is called convergent beam electron diffraction (CBED). This is good for determining the symmetry of materials. A third is precession electron diffraction, where a parallel beam is spun around a large angle, producing a type of average diffraction pattern. These often have less multiple scattering.
Aberration-corrected transmission electron microscopy (AC-TEM) is the general term for electron microscopes where electro optical components are introduced to reduce the aberrations that would otherwise limit the resolution
of the images. Historically electron microscopes had quite severe
aberrations, and until about the start of the 21st century the
resolution was limited, able to image the atomic structure of materials
if the atoms were far enough apart. Around the turn of the century the electron optical components were
coupled with computer control of the lenses and their alignment,
enabling correction of aberrations. The first demonstration of
aberration correction in TEM mode was by Harald Rose and Maximilian Haider in 1998 using a hexapole corrector, and in STEM mode by Ondrej Krivanek and Niklas Dellby in 1999 using a quadrupole/octupole corrector.
As of 2025 correction of geometric aberrations is standard in many commercial electron microscopes, and they are extensively used in many different areas of science. Similar correctors have also been used at much lower energies for LEEM instruments.
Samples for electron microscopes mostly cannot be observed directly.
The samples need to be prepared to stabilize the sample and enhance
contrast. Preparation techniques differ vastly in respect to the sample
and its specific qualities to be observed as well as the specific
microscope used. Details can be found in the relevant main articles
listed above.
Disadvantages
JEOL transmission and scanning electron microscope made in the mid-1970s
Electron microscopes are expensive to build and maintain. Microscopes
designed to achieve high resolutions must be housed in stable buildings
(sometimes underground) with special services such as magnetic field
canceling systems and anti vibration mounts.
The samples largely have to be viewed in vacuum, as the molecules that make up air would scatter the electrons. An exception is liquid-phase electron microscopy[60] using either a closed liquid cell or an environmental chamber, for example, in the environmental scanning electron microscope, which allows hydrated samples to be viewed in a low-pressure (up to 20 Torr or 2.7 kPa) wet environment. Various techniques for in situ electron microscopy of gaseous samples have also been developed.
Pleolipoviral virion (HRPV-6)
Samples of hydrated materials, including almost all biological
specimens, have to be prepared in various ways to stabilize them, reduce
their thickness (ultrathin sectioning) and increase their electron
optical contrast (staining). These processes may result in artifacts,
but these can usually be identified by comparing the results obtained
by using radically different specimen preparation methods. Since the
1980s, analysis of cryofixed, vitrified specimens has also become increasingly used.
Many samples suffer from radiation damage which can change internal structures. This can be due to either or both radiolytic processes or ballistic, for instance with collision cascades. This can be a severe issue for biological samples.
Scientific racism, sometimes termed biological racism, is the pseudoscientific belief that the human species is divided into biologically distinct taxa called "races", and that empirical evidence exists to support or justify racial discrimination, racial inferiority, or racial superiority. Before the mid-20th century, scientific racism was accepted throughout
the scientific community, but it is no longer considered scientific. The division of humankind into biologically separate groups, along with
the assignment of particular physical and mental characteristics to
these groups through constructing and applying corresponding explanatory models, is referred to as racialism, racial realism, race realism, or race science by those who support these ideas. Modern scientific consensus rejects this view as being irreconcilable with modern genetic research.
Scientific racism was common during the period from the 1600s to the end of World War II,
and was particularly prominent in European and American academic
writings from the mid-19th century through the early-20th century. Since
the second half of the 20th century, scientific racism has been
discredited and criticized as obsolete and actively harmful, yet has
persistently been used to support or validate racist world-views based
upon belief in the existence and significance of racial categories and a
hierarchy of superior and inferior races.
During the 20th century, anthropologist Franz Boas and biologists Julian Huxley and Lancelot Hogben
were among the earliest leading critics of scientific racism.
Skepticism towards the validity of scientific racism grew during the interwar period, and by the end of World War II, scientific racism in theory and action was formally denounced, especially in UNESCO's early antiracist statement, "The Race Question"
(1950): "The biological fact of race and the myth of 'race' should be
distinguished. For all practical social purposes, 'race' is not so much a
biological phenomenon as a social myth. The myth of 'race' has created
an enormous amount of human and social damage. In recent years, it has
taken a heavy toll in human lives, and caused untold suffering". Since that time, developments in human evolutionary genetics and physical anthropology
have led to a new consensus among anthropologists that human races are a
sociopolitical phenomenon rather than a biological one.
The term scientific racism was popularized by Stephen Jay Gould who used it in his 1981 book The Mismeasure of Man to describe the historical role of science in propagating the ideal of white racial superiority. Today, the term is generally used pejoratively when applied to more modern theories, such as those in The Bell Curve (1994). Critics argue that such works postulate racist conclusions, such as a genetic connection between race and intelligence, that are unsupported by available evidence. Publications such as the Mankind Quarterly,
founded explicitly as a "race-conscious" journal, are generally
regarded as platforms of scientific racism because they publish fringe
interpretations of human evolution, intelligence, ethnography, language, mythology, archaeology, and race.
Antecedents
Enlightenment thinkers
During the Age of Enlightenment (an era from the 1650s to the 1780s), concepts of monogenism and polygenism
became popular, though they would only be systematized
epistemologically during the 19th century. Monogenism contends that all
races have a single origin, while polygenism is the idea that each race
has a separate origin. Until the 18th century, the words "race" and
"species" were interchangeable.
François Bernier
François Bernier
(1620–1688) was a French physician and traveller. In 1684, he published
a brief essay dividing humanity into what he called "races",
distinguishing individuals, particularly women, by skin color and a few
other physical traits. The article was published anonymously in the Journal des Savants,
the earliest academic journal published in Europe, and titled "New
Division of the Earth by the Different Species or 'Races' of Man that
Inhabit It".
In the essay, he distinguished four different races:
The first race included populations from Europe, North Africa, the Middle East, India, south-east Asia, and the Americas
The second race consisted of the sub-Saharan Africans
The third race consisted of the east- and northeast Asians
A product of French salon
culture, the essay placed an emphasis on different kinds of female
beauty. Bernier emphasized that his novel classification was based on
his personal experience as a traveler in different parts of the world.
Bernier offered a distinction between essential genetic differences and
accidental ones that depended on environmental factors. He also
suggested that the latter criterion might be relevant to distinguish
sub-types. His biological classification of racial types never sought to go beyond
physical traits, and he also accepted the role of climate and diet in
explaining degrees of human diversity. Bernier had been the first to
extend the concept of "species of man" to racially classify the entirety
of humanity, but he did not establish a cultural hierarchy between the
so-called "races" that he had conceived. On the other hand, he clearly
placed white Europeans as the norm from which other "races" deviated.
The qualities which he attributed to each race were not strictly Eurocentric,
because he thought that peoples of temperate Europe, the Americas, and
India—although culturally very different from one another—belonged to
roughly the same racial group, and he explained the differences between
the civilizations of India (his main area of expertise) and Europe
through climate and institutional history. By contrast, he emphasized
the biological difference between Europeans and Africans, and made very
negative comments towards the Sámi (Lapps) of the coldest climates of
Northern Europe, and about Africans living at the Cape of Good Hope.
For example, Bernier wrote: "The 'Lappons' compose the 4th race. They
are a small and short race with thick legs, wide shoulders, a short
neck, and a face that I don't know how to describe, except that it's
long, truly awful, and seems reminiscent of a bear's face. I've only
ever seen them twice in Danzig, but according to the portraits I've seen, and from what I've heard from a number of people, they're ugly animals". The significance of Bernier's ideology for the emergence of what
Joan-Pau Rubiés called the "modern racial discourse" has been debated,
with Siep Stuurman considering it the beginning of modern racial
thought, while Rubiés believes it is less significant if Bernier's entire view of humanity is taken into account.
An early scientist who studied race was Robert Boyle (1627–1691), an Anglo-Irishnatural philosopher, chemist, physicist, and inventor. Boyle believed in what today is called monogenism, that is, that all races, no matter how diverse, came from the same source: Adam and Eve. He studied reported stories of parents' giving birth to differently coloured albinos,
so he concluded that Adam and Eve were originally white, and that
whites could give birth to different coloured races. Theories of Robert Hooke and Isaac Newton about color and light via optical dispersion in physics were also extended by Robert Boyle into discourses of polygenesis, speculating that perhaps these differences were due to "seminal
impressions". However, Boyle's writings mentioned that at his time, for
"European Eyes", beauty was not measured so much in colour, but in
"stature, comely symmetry of the parts of the body, and good features in
the face". Various members of the scientific community rejected his views, and described them as "disturbing" or "amusing".
Richard Bradley
Richard Bradley (1688–1732) was an English naturalist. In his book titled Philosophical Account of the Works of Nature
(1721), Bradley claimed there to be "five sorts of men" based on their
skin colour and other physical characteristics: white Europeans with
beards; white men in America without beards (meaning Native Americans);
men with copper-coloured skin, small eyes, and straight black hair;
Blacks with straight black hair; and Blacks with curly hair. It has been
speculated that Bradley's account inspired Linnaeus' later
categorisation.
The Scottish lawyer Henry Home, Lord Kames (1696–1782) was a polygenist; he believed God had created different races on Earth in separate regions. In his 1734 book Sketches on the History of Man,
Home claimed that the environment, climate, or state of society could
not account for racial differences, so the races must have come from
distinct, separate stocks.
Carl Linnaeus
Homo monstrosus, or Patagonian giants, from Voyage au pole sud et dans l'Océanie (Voyage to the South Pole, and in Oceania), by Jules Dumont d'Urville
Carl Linnaeus (1707–1778), the Swedish physician, botanist, and zoologist, modified the established taxonomic bases of binomial nomenclature for fauna and flora, and also made a classification of humans into different subgroups. In the twelfth edition of Systema Naturae (1767), he labeled five "varieties" of human species.
Each one was described as possessing the following physiognomic characteristics "varying by culture and place":
The Americanus: red, choleric, upright; black, straight,
thick hair; nostrils flared; face freckled; beardless chin; stubborn,
zealous, free; painting themself with red lines; governed by habit.
The Europeanus:
white, sanguine, muscular; with yellowish, long hair; blue eyes;
gentle, acute, inventive; covered with close vestments; governed by
customs.
The Asiaticus: yellow, melancholic, stiff; black hair, dark eyes; austere, haughty, greedy; covered with loose clothing; governed by beliefs.
The Afer or Africanus: black, phlegmatic, relaxed; black, frizzled hair; silky skin, flat nose, tumid lips; females with elongated labia; mammary glands give milk abundantly; sly, lazy, negligent; anoints themself with grease; governed by caprice.
The Monstrosus were mythologic humans which did not appear in the first editions of Systema Naturae. The sub-species included: the "four-footed, mute, hairy" Homo feralis (Feral man); the animal-reared Juvenis lupinus hessensis (Hessian wolf boy); the Juvenis hannoveranus (Hannoverian boy); the Puella campanica (Wild-girl of Champagne); the agile, but faint-hearted Homo monstrosus (Monstrous man); the Patagonian giant; the Dwarf of the Alps; and the monorchidKhoikhoi (Hottentot). In Amoenitates academicae (1763), Linnaeus presented the mythologicHomo anthropomorpha (Anthropomorphic man), or humanoid creatures, such as the troglodyte, the satyr, the hydra, and the phoenix, incorrectly identified as simian creatures.
There are disagreements about the basis for Linnaeus' human taxa. On
the one hand, his harshest critics say the classification was not only
ethnocentric, but seemed to be based upon skin colour. Renato G.
Mazzolini argued that classifications based on skin colour, at its core,
were a white/black polarity, and that Linnaeus' thinking became
paradigmatic for later racist beliefs. On the other hand, Quintyn (2010) points out that some authors believed
that Linnaeus' classification was based upon geographical distribution,
being cartographically-based, and not hierarchical. In the opinion of Kenneth A. R. Kennedy
(1976), Linnaeus certainly considered his own culture as superior, but
his motives for the classification of human varieties were not
race-centered. Paleontologist Stephen Jay Gould
(1994) argued that the taxa was "not in the ranked order favored by
most Europeans in the racist tradition", and that Linnaeus' division was
influenced by the medical theory of humors, which said that a person's temperament may be related to biological fluids. In a 1994 essay, Gould added: "I don't mean to deny that Linnaeus held
conventional beliefs about the superiority of his own European variety
over others... nevertheless, and despite these implications, the overt
geometry of Linnaeus' model is not linear or hierarchical".
In a 2008 essay published by the Linnean Society of London,
Marie-Christine Skuncke interpreted Linnaeus' statements as reflecting a
view that "Europeans' superiority resides in "culture", and that the
decisive factor in Linnaeus' taxa was "culture", not race". Thus, regarding this topic, Skuncke considers Linnaeus' view as merely "eurocentric",
arguing that Linnaeus never called for racist action, and did not use
the word "race", which was only introduced later "by his French
opponent, Buffon". However, the anthropologist Ashley Montagu, in his book Man's Most Dangerous Myth: the Fallacy of Race, points out that Buffon, indeed "the enemy of all rigid classifications", was diametrically opposed to such broad categories, and did not use the
word "race" to describe them. "It was quite clear, after reading
Buffon, that he uses the word in no narrowly defined, but rather in a
general sense", wrote Montagu, pointing out that Buffon did employ the French word la race,
but as a collective term for whatever population he happened to be
discussing at the time; for instance: "The Danish, Swedish, and
Muscovite Laplanders, the inhabitants of Nova-Zembla, the Borandians,
the Samoiedes, the Ostiacks of the old continent, the Greenlanders, and
the savages to the north of the Esquimaux Indians, of the new continent,
appear to be of one common race".
Scholar Stanley A. Rice agrees that Linnaeus' classification was not meant to "imply a hierarchy of humanness or superiority"; however, modern critics regard Linnaeus' classification as obviously stereotyped and erroneous for having included anthropological, non-biological features, such as customs or traditions.
Charles White
Charles White
Charles White (1728–1813), an English physician and surgeon, believed that races occupied different stations in the "Great Chain of Being",
and he tried to scientifically prove that human races had distinct
origins from each other. He speculated that whites and Negroes were two
different species. White was a believer in polygeny, the idea that different races had been created separately. His Account of the Regular Gradation in Man (1799) provided an empirical basis for this idea. White defended the theory of polygeny by rebutting French naturalist Georges-Louis Leclerc, Comte de Buffon's
interfertility argument, which said that only the same species can
interbreed. White pointed to species hybrids, such as foxes, wolves, and jackals,
which were separate groups that were still able to interbreed. For
White, each race was a separate species, divinely created for its own
geographical region.
Buffon and Blumenbach
Johann Friedrich Blumenbach
The French naturalist Georges-Louis Leclerc, Comte de Buffon (1707–1788) and the German anatomist Johann Blumenbach (1752–1840) were proponents of monogenism, the concept that all races have a single origin. Buffon and Blumenbach believed a "degeneration theory" of the origins of racial difference. Both asserted that Adam and Eve were white, and that other races came about by degeneration owing to environmental factors, such as climate, disease, and diet. According to this model, Negroid pigmentation arose because of the heat of the tropical sun; that cold wind caused the tawny colour of the Eskimos; and that the Chinese had fairer skins than the Tartars, because the former kept mostly in towns, and were protected from environmental factors. Environmental factors, poverty, and hybridization could make races
"degenerate", and differentiate them from the original white race by a
process of "raciation". Interestingly, both Buffon and Blumenbach believed that the
degeneration could be reversed if proper environmental control was
taken, and that all contemporary forms of man could revert to the
original white race.
According to Blumenbach, there are five races, all belonging to a single species: Caucasian, Mongolian, Negroid, American, and the Malay race.
Blumenbach stated: "I have allotted the first place to the Caucasian
for the reasons given below, which make me esteem it the primeval one".
Before James Hutton
and the emergence of scientific geology, many believed the Earth was
only 6,000 years old. Buffon had conducted experiments with heated balls
of iron, which he believed were a model for the Earth's core, and
concluded that the Earth was 75,000 years old, but did not extend the
time since Adam and the origin of humanity back more than 8,000 years—not much further than the 6,000 years of the prevailing Ussher chronology subscribed to by most of the monogenists. Opponents of monogenism believed that it would have been difficult for races to change markedly in such a short period of time.
Benjamin Rush
Benjamin Rush (1745–1813), a Founding Father of the United States and a physician, proposed that being black was a hereditary skin disease,
which he called "negroidism", and that it could be cured. Rush believed
non-whites were actually white underneath, but that they were stricken
with a non-contagious form of leprosy,
which darkened their skin color. Rush drew the conclusion that "whites
should not tyrannize over [blacks], for their disease should entitle
them to a double portion of humanity. However, by the same token, whites
should not intermarry with them, for this would tend to infect
posterity with the 'disorder'... attempts must be made to cure the
disease".
Christoph Meiners
Christoph Meiners
Christoph Meiners (1747–1810) was a German polygenist,
and believed that each race had a separate origin. Meiners studied the
physical, mental, and moral characteristics of each race, and built a
race hierarchy based on his findings. Meiners split mankind into two
divisions, which he labelled the "beautiful white race" and the "ugly black race". In his book titled The Outline of History of Mankind,
Meiners argued that a main characteristic of race is either beauty or
ugliness. Meiners thought only the white race to be beautiful, and
considered ugly races to be inferior, immoral, and animal-like. Meiners
wrote about how the dark, ugly peoples were differentiated from the
white, beautiful peoples by their "sad" lack of virtue and their
"terrible vices".
Meiners hypothesized about how the Negro felt less pain than any
other race, and lacked in emotions. Meiners wrote that the Negro had
thick nerves, and thus, was not sensitive like the other races. He went
so far as to say that the Negro possessed "no human, barely any animal,
feeling". Meiners described a story where a Negro was condemned to death
by being burned alive. Halfway through the burning, the Negro asked to
smoke a pipe, and smoked it like nothing was happening while he
continued to be burned alive. Meiners studied the anatomy of the Negro, and came to the conclusion that Negroes were all carnivores,
based upon his observations that Negroes had bigger teeth and jaws than
any other race. Meiners claimed the skull of the Negro was larger, but
the brain of the Negro was smaller than any other race. Meiners
theorized that the Negro was the most unhealthy race on Earth because of
its poor diet, mode of living, and lack of morals.
Meiners studied the diet of the Americans, and said they fed off any kind of "foul offal",
and consumed copious amounts of alcohol. He believed their skulls were
so thick that the blades of Spanish swords shattered on them. Meiners
also claimed the skin of an American is thicker than that of an ox.
Meiners wrote that the noblest race was the Celts.
This was based upon assertions that they were able to conquer various
parts of the world, they were more sensitive to heat and cold, and their
delicacy is shown by the way they are selective about what they eat.
Meiners claimed that Slavs
are an inferior race, "less sensitive and content with eating rough
food". He described stories of Slavs allegedly eating poisonous fungi
without coming to any harm. He claimed that their medical techniques
were also counterproductive; as an example, Meiners described their
practice of warming up sick people in ovens, then making them roll in
the snow.
Later thinkers
Thomas Jefferson
Thomas Jefferson (1743–1826) was an American politician, scientist, and slave owner. His contributions to scientific racism have been noted
by many historians, scientists, and scholars. According to an article
published in the McGill Journal of Medicine: "One of the most
influential pre-Darwinian racial theorists, Jefferson's call for science
to determine the obvious 'inferiority' of African Americans is an
extremely important stage in the evolution of scientific racism". Writing for The New York Times, historian Paul Finkelman
described how as "a scientist, Jefferson nevertheless speculated that
blackness might come 'from the color of the blood,' and concluded that
blacks were 'inferior to the whites in the endowments of body and
mind'". In his "Notes on the State of Virginia", Jefferson described black people as follows:
They seem to require less sleep. A black, after hard
labor through the day, will be induced by the slightest amusements to
sit up till midnight, or later, though knowing he must be out with the
first dawn of the morning. They are at least as brave, and more
adventuresome. But, this may perhaps proceed from a want of forethought,
which prevents their seeing a danger till it be present. When present,
they do not go through it with more coolness or steadiness than the
whites. They are more ardent after their female: but love seems with
them to be more an eager desire, than a tender delicate mixture of
sentiment and sensation. Their griefs are transient. Those numberless
afflictions, which render it doubtful whether heaven has given life to
us in mercy or in wrath, are less felt, and sooner forgotten with them.
In general, their existence appears to participate more of sensation
than reflection... Comparing them by their faculties of memory, reason,
and imagination, it appears to me, that in memory, they are equal to the
whites; in reason, much inferior, as I think one [black] could scarcely
be found capable of tracing and comprehending the investigations of
Euclid; and that in imagination, they are dull, tasteless, and
anomalous... I advance it, therefore, as a suspicion only, that the
blacks, whether originally a distinct race, or made distinct by time and
circumstances, are inferior to the whites in the endowments both of
body and mind.
However, by 1791, Jefferson had to reassess his earlier suspicions of
whether blacks were capable of intelligence when he was presented with a
letter and almanac from Benjamin Banneker,
an educated black mathematician. Delighted to have discovered
scientific proof for the existence of black intelligence, Jefferson
wrote to Banneker:
No body wishes more than I do to see such proofs as you
exhibit, that nature has given to our black brethren, talents equal to
those of the other colors of men, & that the appearance of a want of
them is owing merely to the degraded condition of their existence both
in Africa & America. I can add with truth that no body wishes more
ardently to see a good system commenced for raising the condition both
of their body & mind to what it ought to be, as fast as the
imbecility of their present existence, and other circumstance which
cannot be neglected, will admit.
Samuel Stanhope Smith
Samuel Stanhope Smith (1751–1819) was an American Presbyterian minister and author of the Essay on the Causes of Variety of Complexion and Figure in the Human Species
(1787). Smith claimed that Negro pigmentation was nothing more than a
huge freckle that covered the whole body as a result of an oversupply of
bile, which was caused by tropical climates.
Georges Cuvier
Georges Cuvier
Racial studies by Georges Cuvier (1769–1832), the French naturalist and zoologist, influenced both scientific polygenism and scientific racism. Cuvier believed there were three distinct races: the Caucasian (white), Mongolian
(yellow), and the Ethiopian (black). He rated each for the beauty or
ugliness of the skull and quality of their civilizations. Cuvier wrote
about Caucasians: "The white race, with oval face, straight hair and
nose, to which the civilised people of Europe belong, and which appear
to us the most beautiful of all, is also superior to others by its
genius, courage, and activity".
Regarding Negroes, Cuvier wrote:
The Negro race ... is marked by black complexion, crisped
or woolly hair, compressed cranium, and a flat nose. The projection of
the lower parts of the face, and the thick lips, evidently approximate
it to the monkey tribe: the hordes of which it consists have always
remained in the most complete state of barbarism.
He thought Adam and Eve
were Caucasian, and hence, the original race of mankind. The other two
races arose by survivors escaping in different directions after a major
catastrophe hit the earth approximately 5,000 years ago. Cuvier
theorized that the survivors lived in complete isolation from each
other, and developed separately as a result.
One of Cuvier's pupils, Friedrich Tiedemann,
was among the first to make a scientific contestation of racism.
Tiedemann asserted that based upon his documentation of craniometric and
brain measurements of Europeans and black people from different parts
of the world, that the then-common European belief that Negroes have
smaller brains, and are thus intellectually inferior, was scientifically
unfounded, and based merely on the prejudice of travellers and
explorers.
Arthur Schopenhauer
Arthur Schopenhauer
The German philosopher Arthur Schopenhauer
(1788–1860) attributed civilizational primacy to the white races, who
gained sensitivity and intelligence via the refinement caused by living
in the rigorous Northern climate:
The highest civilization and culture, apart from the ancient Hindus and Egyptians,
are found exclusively among the white races; and even with many dark
peoples, the ruling caste, or race, is fairer in colour than the rest,
and has, therefore, evidently immigrated, for example, the Brahmins, the Inca, and the rulers of the South Sea Islands.
All this is due to the fact that necessity is the mother of invention,
because those tribes that emigrated early to the north, and there
gradually became white, had to develop all their intellectual powers,
and invent and perfect all the arts in their struggle with need, want,
and misery, which, in their many forms, were brought about by the
climate. This they had to do to make up for the parsimony of nature, and out of it all came their high civilization.
Racial theories in physical anthropology (1850–1918)
A late-19th-century illustration by H. Strickland Constable shows an alleged similarity between "Irish Iberian" and "Negro" features in contrast to the higher "Anglo-Teutonic".
The scientific classification established by Carl Linnaeus is requisite to any human racial classification scheme. In the 19th century, unilineal evolution, or classical social evolution, was a conflation of competing sociologic and anthropologic theories proposing that Western European culture was the acme of human socio-cultural evolution. The Christian Bible was interpreted to sanction slavery and from the 1820s to the 1850s was often used in the antebellum Southern United States, by writers such as the Rev. Richard Furman and Thomas R. R. Cobb, to enforce the idea that Negroes had been created inferior, and thus suited to slavery.
The French aristocrat and writer Arthur de Gobineau (1816–1882), is best known for his book An Essay on the Inequality of the Human Races (1853–55) which proposed three human races (black, white and yellow) were natural barriers and claimed that race mixing
would lead to the collapse of culture and civilization. He claimed that
"The white race originally possessed the monopoly of beauty,
intelligence and strength" and that any positive accomplishments or
thinking of blacks and Asians were due to an admixture with whites. His
works were praised by many white supremacist American pro-slavery
thinkers such as Josiah C. Nott and Henry Hotze.
Gobineau believed that the different races originated in
different areas, the white race had originated somewhere in Siberia, the
Asians in the Americas and the blacks in Africa. He believed that the
white race was superior, writing:
I will not wait for the friends of
equality to show me such and such passages in books written by
missionaries or sea captains, who declare some Wolof is a fine
carpenter, some Hottentot a good servant, that a Kaffir dances and plays
the violin, that some Bambara knows arithmetic... Let us leave aside
these puerilities and compare together not men, but groups.
Gobineau later used the term "Aryans" to describe the Germanic peoples (la race germanique).
Gobineau's works were also influential to the Nazi Party, which published his works in German. They played a key role in the master race theory of Nazism.
Carl Vogt
Carl Vogt in 1870
Another polygenist evolutionist was Carl Vogt
(1817–1895) who believed that the Negro race was related to the ape. He
wrote the white race was a separate species to Negroes. In Chapter VII
of his Lectures of Man (1864) he compared the Negro to the white
race whom he described as "two extreme human types". The difference
between them, he claimed are greater than those between two species of
ape; and this proves that Negroes are a separate species from the
whites.
Charles Darwin
Charles Darwin in 1868
Charles Darwin's
views on race have been a topic of much discussion and debate.
According to Jackson and Weidman, Darwin was a moderate in the 19th
century debates about race. "He was not a confirmed racist — he was a
staunch abolitionist, for example — but he did think that there were
distinct races that could be ranked in a hierarchy".
Darwin's influential 1859 book On the Origin of Species did not discuss human origins. The extended wording on the title page, which adds by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, uses the general terminology of biological races as an alternative for "varieties" such as "the several races, for instance, of the cabbage", and does not carry the modern connotation of human races. In The Descent of Man, and Selection in Relation to Sex
(1871), Darwin examined the question of "Arguments in favour of, and
opposed to, ranking the so-called races of man as distinct species" and
reported no racial distinctions that would indicate that human races are
discrete species.
The historian Richard Hofstadter wrote:
Although Darwinism was not the
primary source of the belligerent ideology and dogmatic racism of the
late nineteenth century, it did become a new instrument in the hands of
the theorists of race and struggle... The Darwinist mood sustained the
belief in Anglo-Saxon racial superiority which obsessed many American
thinkers in the latter half of the nineteenth century. The measure of
world domination already achieved by the 'race' seemed to prove it the
fittest.
According to the historian Gertrude Himmelfarb, "The subtitle of [The Origin of Species]
made a convenient motto for racists: 'The Preservation of Favoured
Races in the Struggle for Life.' Darwin, of course, took 'races' to mean
varieties or species; but it was no violation of his meaning to extend
it to human races.... Darwin himself, in spite of his aversion to
slavery, was not averse to the idea that some races were more fit than
others".
On the other hand, Robert Bannister defended Darwin on the issue
of race, writing that "Upon closer inspection, the case against Darwin
himself quickly unravels. An ardent opponent of slavery, he consistently
opposed the oppression of nonwhites... Although by modern standards The Descent of Man
is frustratingly inconclusive on the critical issues of human equality,
it was a model of moderation and scientific caution in the context of
midcentury racism".
According to Myrna Perez Sheldon, Darwin believed that different
races gained their 'population-level characteristics' via sexual
selection. Previously, race theorists conceptualized race as a 'stable
blood essence' and that these 'essences' mixed when miscegenation
occurred.
Herbert Hope Risley
Herbert Hope Risley
As an exponent of "race science", colonial administrator Herbert Hope Risley (1851–1911) used the ratio of the width of a nose to its height to divide Indian people into Aryan and Dravidian races, as well as seven castes.
Ernst Haeckel
Ernst Haeckel
Ernst Haeckel (1834–1919) supported a doctrine of evolutionary polygenism based on the ideas of the linguist and polygenist August Schleicher, in which several different language groups had arisen separately from speechless prehuman Urmenschen
(German for 'original humans'), which themselves had evolved from
simian ancestors. These separate languages had completed the transition
from animals to man, and, under the influence of each main branch of
languages, humans had evolved as separate species, which could be
subdivided into races. Haeckel divided human beings into ten races, of
which the Caucasian was the highest and the primitives were doomed to
extinction. Haeckel was also an advocate of the out of Asia theory by writing that the origin of humanity was to be found in Asia; he believed that Hindustan
(South Asia) was the actual location where the first humans had
evolved. Haeckel argued that humans were closely related to the primates
of Southeast Asia and rejected Darwin's hypothesis of Africa.
Haeckel also wrote that Negroes have stronger and more freely
movable toes than any other race which is evidence that Negroes are
related to apes because when apes stop climbing in trees they hold on to
the trees with their toes. Haeckel compared Negroes to "four-handed"
apes. Haeckel also believed Negroes were savages and that whites were
the most civilised.
The Dutch scholar Pieter Camper
(1722–89), an early craniometric theoretician, used "craniometry"
(interior skull-volume measurement) to scientifically justify racial
differences. In 1770, he conceived of the facial angle
to measure intelligence among species of men. The facial angle was
formed by drawing two lines: a horizontal line from nostril to ear; and a
vertical line from the upper-jawbone prominence to the forehead
prominence. Camper's craniometry reported that antique statues (the
Greco-Roman ideal) had a 90-degree facial angle, whites an 80-degree
angle, blacks a 70-degree angle, and the orangutan a 58-degree facial angle—thus he established a racist biological hierarchy for mankind, per the Decadent conception of history. Such scientific racist researches were continued by the naturalist Étienne Geoffroy Saint-Hilaire (1772–1844) and the anthropologist Paul Broca (1824–1880).
Samuel George Morton
Racialist differences: "a Negro head ... a Caucasian skull ... a Mongol head", Samuel George Morton, 1839
In the 19th century, an early American physical anthropologist, physician and polygenist Samuel George Morton
(1799–1851), collected human skulls from worldwide, and attempted a
logical classification scheme. Influenced by contemporary racialist
theory, Dr Morton said he could judge racial intellectual capacity by
measuring the interior cranial capacity, hence a large skull denoted a large brain, thus high intellectual
capacity. Conversely, a small skull denoted a small brain, thus low
intellectual capacity; superior and inferior established. After
inspecting three mummies from ancient Egyptian catacombs, Morton
concluded that Caucasians and Negroes were already distinct three
thousand years ago. Since interpretations of the bible indicated that Noah's Ark had washed up on Mount Ararat
only a thousand years earlier, Morton claimed that Noah's sons could
not possibly account for every race on earth. According to Morton's
theory of polygenesis, races have been separate since the start.
In Morton's Crania Americana, his claims were based on craniometry
data, that the Caucasians had the biggest brains, averaging 87 cubic
inches, Native Americans were in the middle with an average of 82 cubic
inches and Negroes had the smallest brains with an average of 78 cubic
inches.
In The Mismeasure of Man (1981), the evolutionary biologist and historian of scienceStephen Jay Gould
argued that Samuel Morton had falsified the craniometric data, perhaps
inadvertently over-packing some skulls, to so produce results that would
legitimize the racist presumptions he was attempting to prove. A
subsequent study by the anthropologist
John Michael found Morton's original data to be more accurate than
Gould describes, concluding that "[c]ontrary to Gould's
interpretation... Morton's research was conducted with integrity". Jason Lewis and colleagues reached similar conclusions as Michael in
their reanalysis of Morton's skull collection; however, they depart from
Morton's racist conclusions by adding that "studies have demonstrated
that modern human variation is generally continuous, rather than
discrete or "racial", and that most variation in modern humans is
within, rather than between, populations".
In 1873, Paul Broca, founder of the Anthropological Society of Paris (1859), found the same pattern of measures—that Crania Americana reported—by weighing specimen brains at autopsy.
Other historical studies, proposing a black race–white race,
intelligence–brain size difference, include those by Bean (1906), Mall
(1909), Pearl (1934), and Vint (1934).
Nicolás Palacios
After the War of the Pacific (1879–83) there was a rise of racial and national superiority ideas among the Chilean ruling class. In his 1918 book physician Nicolás Palacios argued for the existence of Chilean race and its superiority when compared to neighboring peoples. He thought Chileans were a mix of two martial races: the indigenous Mapuches and the Visigoths of Spain, who descended ultimately from Götaland in Sweden. Palacios argued on medical grounds against immigration to Chile from southern Europe claiming that Mestizos who are of south European stock lack "cerebral control" and are a social burden.
Samuel Morton's followers, especially Dr Josiah C. Nott (1804–1873) and George Gliddon (1809–1857), extended Dr Morton's ideas in Types of Mankind (1854), claiming that Morton's findings supported the notion of polygenism (mankind has discrete genetic ancestries; the races are evolutionarily unrelated), which is a predecessor of the modern human multiregional origin hypothesis. Moreover, Morton himself had been reluctant to espouse polygenism, because it theologically challenged the Christian creation myth espoused in the Bible.
Later, in The Descent of Man (1871), Charles Darwin proposed the single-origin hypothesis, i.e., monogenism—mankind
has a common genetic ancestry, the races are related, opposing
everything that the polygenism of Nott and Gliddon proposed.
One of the first typologies used to classify various human races was invented by Georges Vacher de Lapouge (1854–1936), a theoretician of eugenics, who published in 1899 L'Aryen et son rôle social ("The Aryan
and his social role"). In this book, he classified humanity into
various, hierarchized races, spanning from the "Aryan white race,
dolichocephalic", to the "brachycephalic", "mediocre and inert" race,
best represented by Southern European, Catholic peasants". Between these, Vacher de Lapouge identified the "Homo europaeus" (Teutonic, Protestant, etc.), the "Homo alpinus" (Auvergnat, Turkish, etc.), and finally the "Homo mediterraneus" (Neapolitan, Andalus,
etc.) Jews were dolichocephalic like the Aryans, according to Lapouge,
but exactly for this reason he considered them to be dangerous; they
were the only group, he thought, threatening to displace the Aryan
aristocracy. Vacher de Lapouge became one of the leading inspirators of Naziantisemitism and Nazi racist ideology.
Vacher de Lapouge's classification was mirrored in William Z. Ripley in The Races of Europe (1899), a book which had a large influence on American white supremacism. Ripley even made a map of Europe according to the alleged cephalic index of its inhabitants. He was an important influence of the American eugenist Madison Grant.
Joseph Deniker
Furthermore, according to John Efron of Indiana University, the late 19th century also witnessed "the scientizing of anti-Jewish prejudice", stigmatizing Jews with male menstruation, pathological hysteria, and nymphomania. At the same time, several Jews, such as Joseph Jacobs or Samuel Weissenberg, also endorsed the same pseudoscientific theories, convinced that the Jews formed a distinct race.Chaim Zhitlovsky also attempted to define Yiddishkayt (Ashkenazi Jewishness) by turning to contemporary racial theory.
Joseph Deniker (1852–1918) was one of William Z. Ripley's
principal opponents; whereas Ripley maintained, as did Vacher de
Lapouge, that the European populace comprised three races, Joseph
Deniker proposed that the European populace comprised ten races (six
primary and four sub-races). Furthermore, he proposed that the concept
of "race" was ambiguous, and in its stead proposed the compound word "ethnic group", which later prominently featured in the works of Julian Huxley and Alfred C. Haddon.
Moreover, Ripley argued that Deniker's "race" idea should be denoted a
"type", because it was less biologically rigid than most racial
classifications.
Ideological applications
Madison Grant, creator of the Nordic race term
Nordicism
Joseph Deniker's contribution to racist theory was La Race nordique (the Nordic race), a generic, racial-stock descriptor, which the American eugenicistMadison Grant
(1865–1937) presented as the white racial engine of world civilization.
Having adopted Ripley's three-race European populace model, but
disliking the Teuton race name, he transliterated la race nordique
into 'the Nordic race', the acme of the concocted racial hierarchy,
based upon his racial classification theory, popular in the 1910s and
1920s.
The State Institute for Racial Biology (Swedish: Statens Institut för Rasbiologi) and its director Herman Lundborg in Sweden were active in racist research. Furthermore, much of early research on Ural-Altaic languages
was coloured by attempts at justifying the view that European peoples
east of Sweden were Asian and thus of an inferior race, justifying
colonialism, eugenics and racial hygiene.The book The Passing of the Great Race
(Or, The Racial Basis of European History) by American eugenicist,
lawyer, and amateur anthropologist Madison Grant was published in 1916.
Though influential, the book was largely ignored when it first appeared,
and it went through several revisions and editions. Nevertheless, the
book was used by people who advocated restricted immigration as
justification for what became known as scientific racism.
Justification of slavery in the United States
Samuel Cartwright, M.D.
In the United States, scientific racism justified Black African slavery to assuage moral opposition to the Atlantic slave trade. In 1972, Alexander Thomas and Samuell Sillen documented how blacks' supposed "primitive mentality"
was used to justify black men as uniquely fitted for bondage. In 1851, in antebellum Louisiana, the physician Samuel A. Cartwright (1793–1863) wrote of slave escape attempts as "drapetomania", a treatable mental illness,
that "with proper medical advice, strictly followed, this troublesome
practice that many Negroes have of running away can be almost entirely
prevented". The term drapetomania (mania of the runaway slave) derives from the Greek δραπέτης (drapetes, 'a runaway [slave]') and μανία (mania, 'madness, frenzy'). Cartwright also described dysaesthesia aethiopica, called "rascality" by overseers. The 1840 United States census
claimed that Northern, free blacks suffered mental illness at higher
rates than did their Southern, enslaved counterparts. Though the census
was later found to have been severely flawed by the American Statistical Association, it became a political weapon against abolitionists. Southern slavers concluded that escaping Negroes were suffering from "mental disorders".
At the time of the American Civil War (1861–1865), the matter of miscegenation prompted studies of ostensible physiological differences between Caucasians and Negroes. Early anthropologists, such as Josiah Clark Nott, George Robins Gliddon, Robert Knox, and Samuel George Morton, aimed to scientifically prove that Negroes were a human species different from the white people; that the rulers of Ancient Egypt
were not African; and that mixed-race offspring (the product of
miscegenation) tended to physical weakness and infertility. After the
Civil War, Southern (Confederacy) physicians wrote textbooks of
scientific racism based upon studies claiming that black freemen
(ex-slaves) were becoming extinct, because they were inadequate to the
demands of being a free man—implying that black people benefited from
enslavement.
In Medical Apartheid, Harriet A. Washington noted the
prevalence of two different views on blacks in the 19th century: the
belief that they were inferior and "riddled with imperfections from head
to toe", and the idea that they did not know true pain and suffering
because of their primitive nervous systems (and that slavery was
therefore justifiable). Washington noted the failure of scientists to
accept the inconsistency between these two viewpoints, writing that:
in the eighteenth and nineteenth
centuries, scientific racism was simply science, and it was promulgated
by the very best minds at the most prestigious institutions of the
nation. Other, more logical medical theories stressed the equality of
Africans and laid poor black health at the feet of their abusers, but
these never enjoyed the appeal of the medical philosophy that justified
slavery and, along with it, our nation's profitable way of life.
Even after the end of the Civil War, some scientists continued to
justify the institution of slavery by citing the effect of topography
and climate on racial development. Nathaniel Shaler, a prominent geologist at Harvard University from 1869 to 1906, published the book Man and the Earth
in 1905 describing the physical geography of different continents and
linking these geologic settings to the intelligence and strength of
human races that inhabited these spaces. Shaler argued that North
American climate and geology was ideally suited for the institution of
slavery.
Scientific racism played a role in establishing apartheid in South Africa. In South Africa, white scientists, like Dudly Kidd, who published The essential Kafir
in 1904, sought to "understand the African mind". They believed that
the cultural differences between whites and blacks in South Africa might
be caused by physiological differences in the brain. Rather than
suggesting that Africans were "overgrown children", as early white
explorers had, Kidd believed that Africans were "misgrown with a
vengeance". He described Africans as at once "hopelessly deficient", yet
"very shrewd".
The Carnegie Commission on the Poor White Problem in South Africa
played a key role in establishing apartheid in South Africa. According
to one memorandum sent to Frederick Keppel, then president of the Carnegie Corporation,
there was "little doubt that if the natives were given full economic
opportunity, the more competent among them would soon outstrip the less
competent whites". Keppel's support for the project of creating the report was motivated
by his concern with the maintenance of existing racial boundaries. The preoccupation of the Carnegie Corporation with the so-called poor
white problem in South Africa was at least in part the outcome of
similar misgivings about the state of poor whites in the southern United
States.
The report was five volumes in length. Around the start of the 20th century, white Americans, and whites
elsewhere in the world, felt uneasy because poverty and economic
depression seemed to strike people regardless of race.
Though the ground work for apartheid began earlier, the report
provided support for this central idea of black inferiority. This was
used to justify racial segregation and discrimination in the following decades. The report expressed fear about the loss of white racial pride, and in
particular pointed to the danger that the poor white would not be able
to resist the process of "Africanisation".
Although scientific racism played a role in justifying and supporting institutional racism
in South Africa, it was not as important in South Africa as it has been
in Europe and the United States. This was due in part to the "poor
white problem", which raised serious questions for supremacists about
white racial superiority. Since poor whites were found to be in the same situation as natives in
the African environment, the idea that intrinsic white superiority could
overcome any environment did not seem to hold. As such, scientific
justifications for racism were not as useful in South Africa.
Racial hygiene was historically tied to traditional notions of public health, but with emphasis on heredity—what philosopher and historian Michel Foucault has called state racism. In 1869, Francis Galton
(1822–1911) proposed the first social measures meant to preserve or
enhance biological characteristics, and later coined the term eugenics. Galton, a statistician, introduced correlation and regression analysis and discovered regression toward the mean. He was also the first to study human differences and inheritance of intelligence with statistical methods. He introduced the use of questionnaires and surveys to collect data on population sets, which he needed for genealogical and biographical works and for anthropometric studies. Galton also founded psychometrics, the science of measuring mental faculties, and differential psychology, a branch of psychology concerned with psychological differences between people rather than common traits.
Like scientific racism, eugenics grew popular in the early 20th century, and both ideas influenced Nazi racial policies and Nazi eugenics. In 1901, Galton, Karl Pearson (1857–1936) and Walter F. R. Weldon (1860–1906) founded the Biometrika scientific journal, which promoted biometrics and statistical analysis of heredity. Charles Davenport (1866–1944) was briefly involved in the review. In Race Crossing in Jamaica (1929), he made statistical arguments that biological and cultural degradation followed white and black interbreeding. Davenport was connected to Nazi Germany before and during World War II. In 1939 he wrote a contribution to the festschrift for Otto Reche (1879–1966), who became an important figure within the plan to remove populations considered "inferior" from eastern Germany.
Early intelligence testing and the Immigration Act of 1924
Before the 1920s, social scientists agreed that whites were superior
to blacks, but they needed a way to prove this to back social policy in
favor of whites. They felt the best way to gauge this was through
testing intelligence. By interpreting the tests to show favor to whites
these test makers' research results portrayed all minority groups very
negatively. In 1908, Henry Goddard translated the Binet intelligence test from French and in 1912 began to apply the test to incoming immigrants on Ellis Island. Some claim that in a study of immigrants Goddard reached the conclusion
that 87% of Russians, 83% of Jews, 80% of Hungarians, and 79% of
Italians were feeble-minded and had a mental age less than 12. Some have also claimed that this information was taken as "evidence" by lawmakers and thus it affected social policy for years. Bernard Davis has pointed out that, in the first sentence of his paper,
Goddard wrote that the subjects of the study were not typical members
of their groups but were selected because of their suspected sub-normal
intelligence. Davis has further noted that Goddard argued that the low
IQs of the test subjects were more likely due to environmental rather
than genetic factors, and that Goddard concluded that "we may be
confident that their children will be of average intelligence and if
rightly brought up will be good citizens". In 1996 the American Psychological Association's Board of Scientific
Affairs stated that IQ tests were not discriminatory towards any
ethnic/racial groups.
In his book The Mismeasure of Man, Stephen Jay Gould argued that intelligence testing results played a major role in the passage of the Immigration Act of 1924 that restricted immigration to the United States. However, Mark Snyderman and Richard J. Herrnstein, after studying the Congressional Record
and committee hearings related to the Immigration Act, concluded "the
[intelligence] testing community did not generally view its findings as
favoring restrictive immigration policies like those in the 1924 Act,
and Congress took virtually no notice of intelligence testing".
Juan N. Franco contested the findings of Snyderman and
Herrnstein. Franco stated that even though Snyderman and Herrnstein
reported that the data collected from the results of the intelligence
tests were in no way used to pass The Immigration Act of 1924, the IQ
test results were still taken into consideration by legislators. As
suggestive evidence, Franco pointed to the following fact: Following the
passage of the immigration act, information from the 1890 census was
used to set quotas based on percentages of immigrants coming from
different countries. Based on these data, the legislature restricted the
entrance of immigrants from southern and eastern Europe into the United
States and allowed more immigrants from northern and Western Europe
into the country. The use of the 1900, 1910 or 1920 census data sets
would have resulted in larger numbers of immigrants from southern and
eastern Europe being allowed into the U.S. However, Franco pointed out
that using the 1890 census data allowed congress to exclude southern and
eastern Europeans (who performed worse on IQ tests of the time than did
western and northern Europeans) from the U.S. Franco argued that the
work Snyderman and Herrnstein conducted on this matter neither proved or
disproved that intelligence testing influenced immigration laws.
Sweden
The Swedish State Institute for Racial Biology,
founded in 1922, was the world's first government-funded institute
performing research into racial biology. It was housed in what is now
the Dean's house at Uppsala and was closed down in 1958.
Following the creation of the first society for the promotion of racial hygiene, the German Society for Racial Hygiene in 1905—a Swedish society was founded in 1909 as the Svenska sällskapet för rashygien, the third in the world. By lobbying Swedish parliamentarians and medical institutes the society
managed to pass a decree creating a government-run institute in the
form of the Swedish State Institute for Racial Biology in 1921. By 1922 the institute was built and opened in Uppsala. It was the first such government-funded institute in the world
performing research into "racial biology" and remains highly
controversial to this day. It was the most prominent institution for the study of "racial science" in Sweden. The goal was to cure criminality, alcoholism and psychiatric problems through research in eugenics and racial hygiene. As a result of the institute's work, a law permitting compulsory sterilization of certain groups was enacted in Sweden in 1934. The second president of the institute Gunnar Dahlberg was highly critical of the validity of the science performed at the institute and reshaped the institute toward a focus on genetics. In 1958 it closed down and all remaining research was moved to the Department of Medical Genetics at Uppsala University.
The Nazi Party and its sympathizers published many books on scientific racism, seizing on the eugenicist and antisemitic
ideas with which they were widely associated, although these ideas had
been in circulation since the 19th century. Books such as Rassenkunde des deutschen Volkes ("Racial Science of the German People") by Hans Günther (first published in 1922) and Rasse und Seele ("Race and Soul") by Ludwig Ferdinand Clauß (de) (published under different titles between 1926 and 1934) attempted to scientifically identify differences between the German, Nordic, or Aryan people and other, supposedly inferior, groups. German schools used these books as texts during the Nazi era. In the early 1930s, the Nazis used racialized scientific rhetoric based on social Darwinismto push its restrictive and discriminatory social policies.
During World War II, Nazi racialist beliefs became anathema in the United States, and Boasians such as Ruth Benedict consolidated their institutional power. After the war, discovery of the Holocaust and Nazi abuses of scientific research (such as Josef Mengele's ethical violations and other war crimes revealed at the Nuremberg Trials) led most of the scientific community to repudiate scientific support for racism.
Propaganda for the Nazi eugenics program began with propaganda for eugenic sterilization. Articles in Neues Volk described the appearance of the mentally ill and the importance of preventing such births. Photographs of mentally incapacitated children were juxtaposed with those of healthy children. The film Das Erbe showed conflict in nature in order to legitimize the Law for the Prevention of Hereditarily Diseased Offspring by sterilization.
Although the child was "the most important treasure of the
people", this did not apply to all children, even German ones, only to
those with no hereditary weaknesses. Nazi Germany's racially based social policies placed the improvement of the Aryan race through eugenics at the center of Nazi ideology. People targeted by this policy included criminals, "degenerates", "dissidents" who opposed the Nazification of Germany, the "feeble minded", Jewish people, homosexuals, the insane, idle and "weak". As they were seen as people who fit the criteria of "life unworthy of life" (German: Lebensunwertes Leben), they should thus not be allowed to procreate and pass on their genes or heritage. Although they were still regarded as "Aryan", Nazi ideology deemed Slavs (i.e., Poles, Russians, Ukrainians, etc.) to be racially inferior to the Germanic master race, suitable for expulsion, enslavement, or even extermination.
In the 20th century, concepts of scientific racism, which sought to
prove the physical and mental inadequacy of groups deemed "inferior",
was relied upon to justify involuntary sterilization programs. Such programs, promoted by eugenicists such as Harry H. Laughlin, were upheld as constitutional by the U.S. Supreme Court in Buck v. Bell (1927). In all, between 60,000 and 90,000 Americans were subjected to involuntary sterilization.
Scientific racism was also used as a justification for the Emergency Quota Act of 1921 and the Immigration Act of 1924
(Johnson–Reed Act), which imposed racial quotas limiting Italian
American immigration to the United States and immigration from other
southern European and eastern European nations. Proponents of these
quotas, who sought to block "undesirable" immigrants, justifying
restrictions by invoking scientific racism.
Lothrop Stoddard published many racialist books on what he saw as the peril of immigration, his most famous being The Rising Tide of Color Against White World-Supremacy
in 1920. In this book he presented a view of the world situation
pertaining to race focusing concern on the coming population explosion
among the "colored" peoples of the world and the way in which "white
world-supremacy" was being lessened in the wake of World War I and the
collapse of colonialism.
Stoddard's analysis divided world politics and situations into
"white", "yellow", "black", "Amerindian", and "brown" peoples and their
interactions. Stoddard argued race and heredity were the guiding factors
of history and civilization, and that the elimination or absorption of
the "white" race by "colored" races would result in the destruction of
Western civilization. Like Madison Grant, Stoddard divided the white
race into three main divisions: Nordic, Alpine, and Mediterranean. He
considered all three to be of good stock, and far above the quality of
the colored races, but argued that the Nordic was the greatest of the
three and needed to be preserved by way of eugenics. Unlike Grant,
Stoddard was less concerned with which varieties of European people were
superior to others (Nordic theory), but was more concerned with what he
called "bi-racialism", seeing the world as being composed of simply
"colored" and "white" races. In the years after the Great Migration and
World War I, Grant's racial theory would fall out of favor in the U.S.
in favor of a model closer to Stoddard's.
Coon's school of thought was the object of increasing opposition in mainstream anthropology after World War II. Ashley Montagu was particularly vocal in denouncing Coon, especially in his Man's Most Dangerous Myth: The Fallacy of Race.
By the 1960s, Coon's approach had been rendered obsolete in mainstream
anthropology, but his system continued to appear in publications by his
student John Lawrence Angel as late as in the 1970s.
By 1954, 58 years after the Plessy v. Ferguson upholding of
racial segregation in the United States, American popular and scholarly
opinions of scientific racism and its sociologic practice had evolved.
In 1960, the journal Mankind Quarterly was founded, which is commonly described as a venue for scientific racism and white supremacy,and as lacking a legitimate scholarly purpose. The journal was founded in 1960, partly in response to the Supreme Court decision Brown v. Board of Education which desegregated the American public school system.
In April 1966, Alex Haley interviewed American Nazi Party founder George Lincoln Rockwell for Playboy.
Rockwell justified his belief that blacks were inferior to whites by
citing a long-discredited 1916 study by G. O. Ferguson which claimed to
show that the intellectual performance of black students was correlated
with their percentage of white ancestry, stating "pure negroes, negroes
three-fourths pure, mulattoes and quadroons have, roughly, 60, 70, 80
and 90 percent, respectively, of white intellectual efficiency". Playboy
later published the interview with an editorial note claiming the study
was a "discredited ... pseudoscientific rationale for racism".
International bodies such as UNESCO
attempted to draft resolutions that would summarize the state of
scientific knowledge about race and issued calls for the resolution of
racial conflicts. In its 1950 "The Race Question", UNESCO did not reject the idea of a biological basis to racial categories, but instead defined a race as: "A race, from the biological standpoint,
may therefore be defined as one of the group of populations
constituting the species Homo sapiens", which were broadly defined as
the Caucasian, Mongoloid, Negroid
races but stated that "It is now generally recognized that intelligence
tests do not in themselves enable us to differentiate safely between
what is due to innate capacity and what is the result of environmental
influences, training and education".
Despite scientific racism being largely dismissed by the
scientific community after World War II, some researchers have continued
to propose theories of racial superiority in the past few decades.These authors themselves, while seeing their work as scientific, may dispute the term racism and may prefer terms such as "race realism" or "racialism". In 2018, British science journalist and author Angela Saini expressed strong concern about the return of these ideas into the mainstream. Saini followed up on this idea with her 2019 book Superior: The Return of Race Science.
One such post-World War II scientific racism researcher is Arthur Jensen. His most prominent work is The g Factor: The Science of Mental Ability
in which he supports the theory that black people are inherently less
intelligent than whites. Jensen argues for differentiation in education
based on race, stating that educators must "take full account of all the facts of [students'] nature". Responses to Jensen criticized his lack of emphasis on environmental factors. Psychologist Sandra Scarr describes Jensen's work as "conjur[ing] up images of blacks doomed to failure by their own inadequacies".
J. Philippe Rushton, president of the Pioneer Fund (Race, Evolution, and Behavior) and a defender of Jensen's The g Factor, also has multiple publications perpetuating scientific racism. Rushton
argues "race differences in brain size likely underlie their
multifarious life history outcomes". Rushton's theories are defended by other scientific racists such as Glayde Whitney. Whitney published works suggesting higher crime rates among people of African descent can be partially attributed to genetics. Whitney draws this conclusion from data showing higher crime rates
among people of African descent across different regions. Other
researchers point out that proponents of a genetic crime-race link are
ignoring confounding social and economic variables, drawing conclusions
from correlations.
Christopher Brand was a proponent of Arthur Jensen's work on racial intelligence differences. Brand's The g Factor: General Intelligence and Its Implications claims black people are intellectually inferior to whites. He argues the best way to combat IQ disparities is to encourage low-IQ women to reproduce with high-IQ men. He faced intense public backlash, with his work being described as a promotion of eugenics. Brand's book was withdrawn by the publisher and he was dismissed from his position at the University of Edinburgh.
Kevin MacDonald, in his Culture of Critique series, used arguments from evolutionary psychology to promote antisemitic theories that Jews as a group have biologically evolved to be highly ethnocentric and hostile to the interests of white people. He asserts Jewish behavior and culture are central causes of antisemitism, and promotes conspiracy theories about alleged Jewish control and influence in government policy and political movements.
Psychologist Richard Lynn has published multiple papers and a book supporting theories of scientific racism. In IQ and the Wealth of Nations, Lynn claims that national GDP is determined largely by national average IQ. He draws this conclusion from the correlation between average IQ and
GDP and argues low intelligence in African nations is the cause of their
low levels of growth. Lynn's theory has been criticized for attributing
causal relationship between correlated statistics. Lynn supports scientific racism more directly in his 2002 paper "Skin
Color and Intelligence in African Americans", where he proposes "the
level of intelligence in African Americans is significantly determined
by the proportion of Caucasian genes". As with IQ and the Wealth of Nations, Lynn's methodology is flawed, and he purports a causal relationship from what is simply correlation.
Nicholas Wade's book (A Troublesome Inheritance)
faced strong backlash from the scientific community, with 142
geneticists and biologists signing a letter describing Wade's work as
"misappropriation of research from our field to support arguments about
differences among human societies".
On June 17, 2020, Elsevier announced it was retracting an article that J. Philippe Rushton and Donald Templer had published in 2012 in the Elsevier journal Personality and Individual Differences. The article falsely claimed that there was scientific evidence that
skin color was related to aggression and sexuality in humans.
The Jena Declaration, published by the German Zoological Society, rejects the idea of human races and distances itself from the racial theories of 20th century scientists. It states that genetic variation between human populations
is smaller than within them, demonstrating that the biological concept
of "races" is invalid. The statement highlights that there are no
specific genes or genetic markers that match with conventional racial categorizations. It also indicates that the idea of "races" is based on racism rather than any scientific factuality.
In the United States, an executive order issued March 27, 2025, by the White House characterized an exhibit on African American art at the Smithsonian Institution as divisive, due in part to its presenting race as not being "a biological reality". Scholar Henry Louis Gates Jr.,
however, had commented a year earlier that although racial categories
are indeed culturally constructed, the degree of genetic diversity of
each individual on the planet actually unifies humanity in that "we are
all mixed".
Clarence Gravlee has written that disparities in the incidence of
such medical conditions as diabetes, stroke, cancer, and low birth
weight should be viewed with a societal lens. He has argued that social inequalities,
not genetic differences between races, are the reason for these
differences. Gravlee has also maintained
that genetic differences between different population groups are based
on climate and geography, not race, and he calls for replacing incorrect
biological explanations of racial disparities with an analysis of the
social conditions that lead to disparate medical outcomes. In his book Is Science Racist,
Jonathan Marks similarly asserts that races exist, though they lack a
natural categorization in the realm of biology. Cultural rules such as
the "one-drop rule"
must be devised to establish categories of race, even if they go
against the natural patterns within our species. According to Marks'
writing, racist ideas propagated by scientists are what make science
racist.
In her book Medical Apartheid Harriet
Washington describes the abuse of Black people in medical research and
experimentation. Black people were tricked into participating in medical
experiments through the use of unclear language on consent forms and a
failure to list the risks and side effects of the treatment. Washington
mentions that, because Black people were denied adequate health care,
they were often desperate for medical help, and medical experimenters
were able to exploit that need. Washington also emphasizes that when
treatments were perfected and refined as a result of those experiments,
Black people almost never benefited from the treatments.
A 2018 statement by the American Society of Human Genetics
(ASHG) expressed alarm at the "resurgence of groups rejecting the value
of genetic diversity and using discredited or distorted genetic
concepts to bolster bogus claims of white supremacy".
The ASHG denounced this as a "misuse of genetics to feed racist
ideologies", and highlighted several factual errors upon which white supremacist
claims have been based. The statement affirms that genetics
"demonstrates that humans cannot be divided into biologically distinct
subcategories" and that it "exposes the concept of racial purity as scientifically meaningless".
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