From Wikipedia, the free encyclopedia
Evolutionary neuroscience is the scientific study of the
evolution of nervous systems. Evolutionary neuroscientists investigate the
evolution and
natural history of
nervous system structure, functions and emergent properties. The field draws on concepts and findings from both
neuroscience and
evolutionary biology. Historically, most empirical work has been in the area of
comparative neuroanatomy, and modern studies often make use of
phylogenetic comparative methods.
Selective breeding and
experimental evolution approaches are also being used more frequently.
Conceptually and theoretically, the field is related to fields as diverse as
cognitive genomics,
neurogenetics,
developmental neuroscience,
neuroethology,
comparative psychology,
evo-devo,
behavioral neuroscience,
cognitive neuroscience,
behavioral ecology,
biological anthropology and
sociobiology.
Evolutionary neuroscientists examine changes in genes, anatomy,
physiology, and behavior to study the evolution of changes in the brain.
[2] They study a multitude of processes including the evolution of
vocal,
visual,
auditory,
taste, and
learning systems as well as
language evolution and development.
[2] [3]In addition, evolutionary neuroscientists study the evolution of specific areas or structures in the brain such as the
amigdala ,
forebrain and
cerebellum as well as the
motor or
visual cortex.
[2]
History
Studies
of the brain began during ancient Egyptian times but studies in the
field of evolutionary neuroscience began after the publication of
Darwin's
On the Origin of Species in 1859.
[4] At that time, brain evolution was largely viewed at the time in relation to the incorrect
scala naturae. Phylogeny and the evolution of the brain were still viewed as linear.
[4] During the early 20th century, there were several prevailing theories about evolution.
Darwinism was based on the principles of natural selection and variation,
Lamarckism was based on the passing down of acquired traits,
Orthogenesis was based on the assumption that tendency towards perfection steers evolution, and
Saltationism argued that discontinuous variation creates new species.
[4] Darwin’s became the most accepted and allowed for people to starting thinking about the way animals and their brains evolve.
[4]
The 1936 book
The Comparative Anatomy of the Nervous System of Vertebrates Including Man
by the Dutch neurologist C.U. Ariëns Kappers (first published in German
in 1921) was a landmark publication in the field. Following the
Evolutionary Synthesis,
the study of comparative neuroanatomy was conducted with an
evolutionary view, and modern studies incorporate developmental
genetics.
[5][6] It is now accepted that phylogenetic changes occur independently between species over time and can not be linear.
[4] It is also believed that an increase with brain size correlates with an increase in neural centers and behavior complexity.
[7]
Major Arguments
Over
time, there are several arguments that would come to define the history
of evolutionary neuroscience. The first is the argument between
Etienne Geoffro St. Hilaire and
George Cuvier over the topic of "common plan versus diversity".
[2] Geoffrey argued that all animals are built based off a single plan or
archetype and he stressed the importance of
homologies
between organisms, while Cuvier believed that the structure of organs
was determined by their function and that knowledge of the function of
one organ could help discover the functions of other organs.
[2][4] He argued that there were at least four different archetypes.
[2] After Darwin, the idea of evolution was more accepted and Geoffrey's idea of homologous structures was more accepted.
[2]The second major argument is that of the
Scala Naturae (scale of nature) versus the phylogenetic bush.
[2]
The Scala Naturae, later also called the phylogenetic scale, was based
on the premise that phylogenies are linear or like a scale while the
phylogenetic bush argument was based on the idea that phylogenies were
nonlinear and resembled a bush more than a scale.
[2] Today it is accepted that phylogenies are nonlinear.
[2]
A third major argument dealt with the size of the brain and whether
relative size or absolute size was more relevant in determining
function.
[2] In the late 18
th century, it was determined that brain to body ratio reduces as body size increases.
[2] However more recently, there is more focus on absolute
brain size as this scales with internal structures and functions, with the degree of structural complexity, and with the amount of
white matter in the brain, all suggesting that absolute size is much better predictor of brain function.
[2] Finally, a fourth argument is that of natural selection (Darwinism) versus developmental constraints (concerted evolution).
[2]
It is now accepted that the evolution of development is what causes
adult species to show differences and evolutionary neuroscientists
maintain that many aspects of brain function and structure are conserved
across species.
[2]
Techniques
Throughout
history, we see how evolutionary neuroscience has been dependent on
developments in biological theory and techniques.
[4]The
field of evolutionary neuroscience has been shaped by the development
of new techniques that allow for the discovery and examination of parts
of the nervous system. In 1873,
Camillo Gogi
devised the silver nitrate method which allowed for the description of
the brain at the cellular level as opposed to simply the gross level.
[4] Santiago Ramon and Pedro Ramon used this method to analyze numerous parts of brains, broadening the field of comparative neuroanatomy.
[4] In the second half of the 19
th century, new techniques allowed scientists to identify neuronal cell groups and fiber bundles in brains.
[4] In 1885,
Vittorio Marchi
discovered a staining technique that let scientists see induced axonal
degeneration in myelinated axons, in 1950, the “original Nauta
procedure” allowed for more accurate identification of degenerating
fibers, and in the 1970s, there were several discoveries of multiple
molecular tracers which would be used for experiments even today.
[4] In the last 20 years,
cladistics has also become a useful tool for looking at variation in the brain.
[7]
Evolution of the Human Brain
Darwin's theory allowed for people to start thinking about the way animals and their brains evolve.
