Factual relativism (also called epistemic relativism, epistemological relativism, alethic relativism, and cognitive relativism)
is the philosophical belief that certain facts are not absolute but
depend on the perspective from which they are being evaluated. It challenges the assumption that all facts are objective and universally valid. According to factual relativism, facts used to justify claims are
shaped by social, cultural, or conceptual frameworks, making them subjective and relative.
History and development
Factual
relativism is rooted in the idea that the standards for what counts as a
rational belief can change depending on cultural or conceptual
perspectives. This challenges the traditional view that there are
objective, universal standards for determining what is true and
rational.
There are three main ideas behind factual relativism. The first
is that the justification of beliefs depends on the context they are
observed from. This challenges the idea of objectivity. The second is
that there are many different perspectives and ways of thinking, some of
which contradict each other. Lastly, factual relativism says that no
perspective is superior to another.
During the Scientific Revolution, Galileo and Cardinal Robert Bellarmine
disagreed about how planets move. Each used a different system. A
relativist would argue that there is no fact of the matter about which
view is supported by the evidence because there are no standards as to
what evidence is true. In contrast, an anti-relativist would say one
theory is better supported by evidence than the other.
Philosopher Thomas Kuhn
influenced discussion of factual relativism with his idea of scientific
paradigms. He argued that what scientists consider facts depends on the
dominant paradigm they work within. These paradigms can shift
drastically during periods of scientific revolutions, which suggests
that scientific facts are not fixed but relative to the paradigm they
arise from.
In anthropology, scholars like Peter Winch have explored how factual relativism plays out in non-Western cultures, such as the people, whose belief in witchcraft
is seen as rational within the context of their culture. This shows how
factual relativism can help explain the legitimacy of different
standards based on cultural context. This sparked debates about whether
it is possible to compare beliefs across cultures using a single
standard of rationality.
Viewpoints
One
perspective compares scientific knowledge to the mythology of other
cultures, arguing that science is merely a societal set of myths based
on societal assumptions. In Against Method, Paul Feyerabend
writes, "The similarities between science and myth are indeed
astonishing" and "First-world science is one science among many". But it
is debated whether Feyerabend intended these statements to be taken
entirely seriously, as they may have been a critique of the claimed
objectivity of science rather than a full endorsement of the idea that
science and myth are equally valid.
The strong program in the sociology of science, in the words of founder David Bloor, argues that it is "impartial with respect to truth and falsity". Elsewhere, Bloor and Barry Barnes
have said "For the relativist [such as us] there is no sense attached
to the idea that some standards or beliefs are really rational as
distinct from merely locally accepted as such." In France, Bruno Latour has claimed that "Since the settlement of a controversy is the cause
of Nature's representation, not the consequence, we can never use the
outcome—Nature—to explain how and why a controversy has been settled."
Yves Winkin,
a Belgian professor of communications, responded to a popular trial in
which two witnesses gave contradicting testimony by telling the
newspaper Le Soir that "There is no transcendent truth. [...] It
is not surprising that these two people, representing two very different
professional universes, should each set forth a different truth. Having
said that, I think that, in this context of public responsibility, the
commission can only proceed as it does."
The philosopher of science Gérard Fourez wrote, "What one
generally calls a fact is an interpretation of a situation that no one,
at least for the moment, wants to call into question."
British archaeologist Roger Anyon told The New York Times that "science is just one of many ways of knowing the world... The Zuni's world view is just as valid as the archeological viewpoint of what prehistory is about."
According to the Stanford Encyclopedia of Philosophy,
"Relativism has been, in its various guises, both one of the most
popular and most reviled philosophical doctrines of our time. Defenders
see it as a harbinger of tolerance and the only ethical and epistemic
stance worthy of the open-minded and tolerant. Detractors dismiss it for
its alleged incoherence and uncritical intellectual permissiveness."
Related views and criticism
This section needs expansion. You can help by adding to it. (July 2017)
Epistemic relativism
Epistemic
relativism has many similarities to factual relativism: both question
the objectivity of truth. According to epistemic relativism, knowledge
depends on context and what counts as rational knowledge depends on
one's perspective. This challenges the idea of objective standards for
evaluating knowledge, just as factual relativism challenges the
existence of objective facts. Critics such as Paul Boghossian
argue that epistemic relativism can lead to epistemic
incommensurability, where different knowledge systems are so distinct
that there is no neutral way to compare or judge them.
The self-excepting fallacy
A primary critique of factual relativism is the self-excepting fallacy, introduced by Maurice Mandelbaum
in 1962. According to this critique, the relativist view is
inconsistent because it requires the relativist to accept a universal
claim about the nature of facts, even though relativism itself denies
the possibility of universal truth. Because of this contradiction, few
authors in the philosophy of science accept cognitive relativism.
Philosophical perspectives on factual relativism
Larry Laudan's book Science and Relativism outlines various viewpoints on factual relativism in the form of a dialogue, presenting different perspectives on knowledge and how it relates to truth, objectivity, and cultural context.
Criticisms of cognitive relativism
Cognitive relativism has been criticized by both analytic philosophers and scientists. Critics argue that relativism's emphasis on knowledge's dependence on
cultural and social contexts undermines the possibility of universal
truth and objective knowledge. It can even be seen as a threat to
scientific inquiry, as the scientific process depends on objective
methods and standards of evidence.
The distinction between subjectivity and objectivity is a basic idea of philosophy, particularly epistemology and metaphysics.
Various understandings of this distinction have evolved through the
work of philosophers over centuries. One basic distinction is:
Something is subjective if it is dependent on minds (such as biases, perception, emotions, opinions, imaginary objects, or conscious experiences). If a claim is true exclusively when considering the claim from the
viewpoint of a sentient being, it is subjectively true. For example, one
person may consider the weather to be pleasantly warm, and another
person may consider the same weather to be too hot; both views are
subjective.
Something is objective if it can be confirmed or assumed
independently of any minds. If a claim is true even when considering it
outside the viewpoint of a sentient being, then it may be labelled
objectively true. For example, many people would regard "2 + 2 = 4" as
an objective statement of mathematics.
Both ideas have been given various and ambiguous definitions by
differing sources as the distinction is often a given but not the
specific focal point of philosophical discourse. The two words are usually regarded as opposites,
though complications regarding the two have been explored in
philosophy: for example, the view of particular thinkers that
objectivity is an illusion and does not exist at all, or that a spectrum
joins subjectivity and objectivity with a gray area in-between, or that
the problem of other minds is best viewed through the concept of intersubjectivity, developing since the 20th century.
The root of the words subjectivity and objectivity are subject and object, philosophical terms that mean, respectively, an observer and a thing being observed. The word subjectivity comes from subject
in a philosophical sense, meaning an individual who possesses unique
conscious experiences, such as perspectives, feelings, beliefs, and
desires, or who (consciously) acts upon or wields power over some other entity (an object).
In different fields
In Ancient philosophy
Aristotle's teacher Plato considered geometry to be a condition of his idealist philosophy concerned with universal truth. In Plato's Republic, Socrates opposes the sophist Thrasymachus's
relativistic account of justice, and argues that justice is
mathematical in its conceptual structure, and that ethics was therefore a
precise and objective enterprise with impartial standards for truth and
correctness, like geometry. The rigorous mathematical treatment Plato gave to moral concepts set
the tone for the western tradition of moral objectivism that came after
him. His contrasting between objectivity and opinion became the basis for philosophies intent on resolving the questions of reality, truth, and existence. He saw opinions as belonging to the shifting sphere of sensibilities, as opposed to a fixed, eternal and knowable incorporeality. Where Plato distinguished between how we know things and their ontological status, subjectivism such as George Berkeley's depends on perception. In Platonic terms, a criticism of subjectivism is that it is difficult to distinguish between knowledge, opinions, and subjective knowledge.
In Western philosophy, the idea of subjectivity is thought to have its roots in the works of the European Enlightenment thinkers Descartes and Kant though it could also stem as far back as the Ancient Greek philosopher Aristotle's work relating to the soul. The idea of subjectivity is often seen as a peripheral to other philosophical concepts, namely skepticism, individuals and individuality, and existentialism.The questions surrounding subjectivity have to do with whether or not
people can escape the subjectivity of their own human existence and
whether or not there is an obligation to try to do so.
Subjectivity was rejected by Foucault and Derrida in favor of constructionism, but Sartre embraced and continued Descartes' work in the subject by emphasizing subjectivity in phenomenology. Sartre believed that, even within the material force of human society,
the ego was an essentially transcendent being—posited, for instance, in
his opus Being and Nothingness through his arguments about the 'being-for-others' and the 'for-itself' (i.e., an objective and subjective human being).
The innermost core of subjectivity resides in a unique act of what Fichte called "self-positing", where each subject is a point of absolute autonomy, which means that it cannot be reduced to a moment in the network of causes and effects.
Religion
One way that subjectivity has been conceptualized by philosophers such as Kierkegaard is in the context of religion. Religious beliefs can vary quite extremely from person to person, but
people often think that whatever they believe is the truth. Subjectivity
as seen by Descartes and Sartre was a matter of what was dependent on
consciousness, so, because religious beliefs require the presence of a
consciousness that can believe, they must be subjective. This is in contrast to what has been proven by pure logic or hard sciences, which does not depend on the perception of people, and is therefore considered objective. Subjectivity is what relies on personal perception regardless of what is proven or objective.
Many philosophical arguments within this area of study have to do
with moving from subjective thoughts to objective thoughts with many
different methods employed to get from one to the other along with a
variety of conclusions reached. This is exemplified by Descartes deductions that move from reliance on
subjectivity to somewhat of a reliance on God for objectivity. Foucault and Derrida denied the idea of subjectivity in favor of their ideas of constructs in order to account for differences in human thought. Instead of focusing on the idea of consciousness and self-consciousness
shaping the way humans perceive the world, these thinkers would argue
that it is instead the world that shapes humans, so they would see
religion less as a belief and more as a cultural construction.
Phenomenology
Others like Husserl and Sartre followed the phenomenological approach. This approach focused on the distinct separation of the human mind and
the physical world, where the mind is subjective because it can take
liberties like imagination and self-awareness where religion might be
examined regardless of any kind of subjectivity. The philosophical conversation around subjectivity remains one that
struggles with the epistemological question of what is real, what is
made up, and what it would mean to be separated completely from
subjectivity.
The importance of perception in evaluating and understanding objective reality is debated in the observer effect of quantum mechanics. Direct or naïve realists rely on perception as key in observing objective reality, while instrumentalists
hold that observations are useful in predicting objective reality. The
concepts that encompass these ideas are important in the philosophy of science. Philosophies of mind explore whether objectivity relies on perceptual constancy.
In historiography
History
as a discipline has wrestled with notions of objectivity from its very
beginning. While its object of study is commonly thought to be the past, the only thing historians have to work with are different versions of stories based on individual perceptions of reality and memory.
Several history streams developed to devise ways to solve this dilemma: Historians like Leopold von Ranke (19th century) have advocated for the use of extensive evidence –especially archived
physical paper documents– to recover the bygone past, claiming that, as
opposed to people's memories, objects remain stable in what they say
about the era they witnessed, and therefore represent a better insight
into objective reality. In the 20th century, the Annales School emphasized the importance of shifting focus away from the perspectives of influential men –usually politicians around whose actions narratives of the past were shaped–, and putting it on the voices of ordinary people. Postcolonial streams of history challenge the colonial-postcolonial dichotomy and critique Eurocentric academia
practices, such as the demand for historians from colonized regions to
anchor their local narratives to events happening in the territories of
their colonizers to earn credibility. All the streams explained above try to uncover whose voice is more or
less truth-bearing and how historians can stitch together versions of it
to best explain what "actually happened."
Trouillot
The anthropologist Michel-Rolph Trouillot developed the concepts of historicity 1 and 2 to explain the difference between the materiality of socio-historical processes (H1) and the narratives that are told about the materiality of socio-historical processes (H2). This distinction hints that H1 would be understood as the factual reality that elapses and is captured with the concept of "objective truth", and that H2 is the collection of subjectivities that humanity has stitched together to grasp the past. Debates about positivism, relativism, and postmodernism are relevant to evaluating these concepts' importance and the distinction between them.
In his book "Silencing the past", Trouillot wrote about the power dynamics at play in history-making, outlining four possible moments in which historical silences can be created: (1) making of sources (who gets to know how to write, or to have possessions that are later examined as historical evidence), (2) making of archives (what documents are deemed important to save and which are not, how to classify materials, and how to order them within physical or digital archives), (3) making of narratives (which accounts of history are consulted, which voices are given credibility), and (4) the making of history (the retrospective construction of what The Past is).
Because history (official, public, familial, personal) informs current perceptions and how we make sense of the present,
whose voice gets to be included in it –and how– has direct consequences
in material socio-historical processes. Thinking of current historical
narratives as impartial
depictions of the totality of events unfolded in the past by labeling
them as "objective" risks sealing historical understanding.
Acknowledging that history is never objective and always incomplete has a
meaningful opportunity to support social justice
efforts. Under said notion, voices that have been silenced are placed
on an equal footing to the grand and popular narratives of the world,
appreciated for their unique insight of reality through their subjective lens.
In social sciences
Subjectivity
is an inherently social mode that comes about through innumerable
interactions within society. As much as subjectivity is a process of individuation,
it is equally a process of socialization, the individual never being
isolated in a self-contained environment, but endlessly engaging in
interaction with the surrounding world.
Culture is a living totality of the subjectivity of any given society
constantly undergoing transformation. Subjectivity is both shaped by it and shapes it in turn, but also by
other things like the economy, political institutions, communities, as
well as the natural world.
Though the boundaries of societies and their cultures are
indefinable and arbitrary, the subjectivity inherent in each one is
palatable and can be recognized as distinct from others. Subjectivity is
in part a particular experience or organization of reality,
which includes how one views and interacts with humanity, objects,
consciousness, and nature, so the difference between different cultures
brings about an alternate experience of existence that forms life in a
different manner. A common effect on an individual of this disjunction
between subjectivities is culture shock, where the subjectivity of the other culture is considered alien and possibly incomprehensible or even hostile.
Political subjectivity is an emerging concept in social sciences and humanities. Political subjectivity is a reference to the deep embeddedness of
subjectivity in the socially intertwined systems of power and meaning.
"Politicality", writes Sadeq Rahimi in Meaning, Madness and Political Subjectivity, "is not an added aspect of the subject, but indeed the mode of being of the subject, that is, precisely what the subject is."
Scientific objectivity is practicing science while intentionally reducing partiality,
biases, or external influences. Moral objectivity is the concept of
moral or ethical codes being compared to one another through a set of
universal facts or a universal perspective and not through differing
conflicting perspectives.
Journalistic objectivity is the reporting of facts and news with minimal personal bias or in an impartial or politically neutral manner.
The blood type personality theory is a pseudoscientific belief prevalent in East Asia that a person's blood type is predictive of a person's personality, temperament, and compatibility with others. The theory is generally considered a superstition by the scientific community.
One of the reasons Japan developed the blood type personality indicator theory was in reaction to a claim from German scientist Emil von Dungern, that blood type B people were inferior. The popular belief originates with publications by Masahiko Nomi in the 1970s.
Although some medical hypotheses have been proposed in support of blood type personality theory, the scientific community generally dismisses blood type personality
theories as superstition or pseudoscience because of lack of evidence or
testable criteria. Although research into the causal link between blood type and
personality is limited, the majority of modern studies do not
demonstrate any statistically significant association between the two. Some studies suggest that there is a statistically significant
relationship between blood type and personality, although it is unclear
if this is simply due to a self-fulfilling prophecy.
Overview
According
to popular belief, people with type A blood are friendly and kind but
also obsessive and anxious, people with type B are spontaneous and
creative but can be selfish, and people with type O are confident but
stubborn and aggressive. In a logical extension of this system, those
with type AB are a mix of stereotypical A and B traits, while also being
seen as mysterious or aloof due to their relatively low population in
Japan. The minority types B and AB are more likely to be negatively
stereotyped than A or O.
History
Machine offering blood-type based fortunes
The idea that personality traits were inherited through the blood dates as far back as Aristotle. Hippocrates also sought to link personality biologically, linking traits with the four bodily humors – sanguine, phlegmatic, choleric, and melancholic.
In 1926, Hayashi Hirano and Tomita Yajima published the article "Blood Type Biological Related" in the Army Medical Journal.
Takeji Furukawa
In
1927, Takeji Furukawa, a professor at Tokyo Women's Teacher's School,
published his paper "The Study of Temperament Through Blood Type" in the
scholarly journal Psychological Research. The idea quickly took
off with the Japanese public despite Furukawa's lack of credentials, and
the militarist government of the time commissioned a study aimed at
breeding ideal soldiers. The study used ten to twenty people for the investigation, thereby
failing to meet the statistical requirements for generalizing the
results to the wider population.
On the other hand, in 1934, Fisher announced the chi-squared test,
which is very popular at present, for the first time. Several scholars
said that they found statistically significant differences in analyzing
Japanese work conducted at that time.
In another study, Furukawa compared the distribution of blood types among two ethnic groups: the Formosans in Taiwan and the Ainu of Hokkaidō. His motivation for the study appears to have come from a political incident: After the Japanese occupation of Taiwan following Japan's invasion of China in 1895,
the inhabitants tenaciously resisted their occupiers. Insurgencies in
1930 and 1931 resulted in the deaths of hundreds of Japanese settlers.
The purpose of Furukawa's studies was to "penetrate the essence
of the racial traits of the Taiwanese, who recently revolted and behaved
so cruelly." Based on a finding that 41.2% of Taiwanese samples had
type O blood, Furukawa assumed that the Taiwanese rebelliousness was
genetic. His reasoning was supported by the fact that among the Ainu,
whose temperament was characterized as submissive, only 23.8% is type O.
In conclusion, Furukawa suggested that the Japanese should increase
intermarriage with the Taiwanese to reduce the number of Taiwanese with
type O blood.
Interest in the theory was revived in the 1970s with a book by Masahiko Nomi,
a journalist with no medical background (he graduated from the
engineering department of the University of Tokyo). Few Japanese
psychologists criticized him at that time, so he continued to demonstrate statistically significant data in various fields and published several books with these results. Later after his death in 1981, Masahiko Nomi's work was said to be
largely uncontrolled and anecdotal, and the methodology of his
conclusions was unclear. Because of this, he was heavily criticized by the Japanese psychological community, although his books remain popular. His son, Toshitaka Nomi, continued to promote the theory with a series of books and by running the Institute of Blood Type Humanics. He later established the Human Science ABO Center for further research and publication in 2004.
Background and criticism
Criticism
Kengo
Nawata, a social psychologist, studied blood type correlations in a
survey of 68 personality traits given to over 10,000 people from Japan
and the US. His statistical analysis found that less than 0.3% of the total variance in personality was explained by blood type.
Controversial statistically significant data
However,
some academic researchers have shown several statistically significant
data in Japan and Korea. Akira Sakamoto and Kenji Yamazaki, Japanese
social psychologists, analyzed 32,347 samples of annual opinion polls
from 1978 through 1988. These results indicated that Japanese blood-typical stereotypes
influenced their self-reported personalities – like a self-fulfilling
prophecy.
Cosy Muto and Masahiro Nagashima et al. (Nagasaki University) conducted a supplementary survey of Yamazaki and Sakamoto in 2011. They demonstrated that significant and the same difference in
personalities between blood-types by using the same database as Samamoto
and Yamazaki used. In the 1990s, the difference due to blood types was
stabilized and variances became smaller. Then in the 2000s, the
difference was statistically significant, too. However, the effect magnitude was extremely small, despite 'significance' in the statistical sense.
Another Japanese social psychologist, Shigeyuki Yamaoka (Shotoku
University), announced results of his questionnaires, which were
conducted in 1999 (1,300 subjects) and 2006 (1,362 subjects), In both cases, the subjects were university students, and only subjects
with enough knowledge of and belief in the "blood-type diagnosis"
showed meaningful differences. He concluded that these differences must
be the influence of mass media, especially TV programs. Yamaoka later examined 6,660 samples from 1999 through 2009 in total and found the same result.
On the other hand, some believe that the statistically meaningful differences according to the
blood types are not explained only by beliefs, nor that they are a
self-fulfilling prophecy. In Japan, the penetration rate of blood-typical personality traits was investigated. Yoriko Watanabe, a
psychologist at Hokkaido University, chose "well-known" traits and
found most traits were known to no more than half of Japanese people
(subjects were university students). A Japanese writer, Masayuki Kanazawa, analyzed these blood-typical traits in combination with data from Yamaoka (1999) that used the same items from Watanabe's penetration survey. If blood-typical differences are caused by penetration (or their
self-recognition), the rate of differences of a trait is proportional to
the rate of its penetration.However, Kanazawa was not able to discover any association with blood-type differences and penetration rates. This result raises doubt about the role of beliefs and self-fulfilling prophecy.
Most reports that demonstrated statistical correlation attribute differences to a self-fulfilling prophecy.
However, no study directly proved the existence of "self-fulfillment".
Therefore, the opinions of researchers are varied at present:
Whether there is a statistical correlation or not;
Whether any statistical correlations are superficial, being caused
by subjects' self-fulfilling prophecy, or if they are truly caused by
the blood type.
Blood-type personality and the five-factor model
The five-factor model
tests were carried out in several countries, including Japan, Korea,
and Taiwan, after the year 2000. These tests were intended to digitize
self-ratings of the "big five" personality traits.
It was expected that differences in self-reported personalities (a
self-fulfilling prophecy) would be detected from the subject who
believed in blood-typical stereotypes. As a result, researchers found no
meaningful statistical difference.
So Ho Cho, a Korean psychologist (Yonsei University), and the
others carried out a questionnaire about blood-typical items to subjects
and discovered statistical differences as expected. However, the difference was not found when the five-factor model for
big five personality traits was administered to the same subjects.
Another Korean researcher Sohn (Yonsei University) re-analyzed Cho's
data. He found that several independent items of the big five personality
test detected differences according to each blood-typical stereotype.
However, these differences became extinct in the process of plural items
being gathered to five factors (big five). If these results are
correct, the five-factor model test cannot detect differences between
the blood types – if such a causal link did indeed exist.
In 2014, a Korean matchmaking company 듀오 Duo conducted a research
survey examined 3,000 couples and found that blood type had no
significant impact on the possibility of a couple getting married.
In 2017, a meta-analysis of studies, using the Big Five
personality test, involving 260,861 subjects found that six genes
affected human personality. However, the coefficient of determination was as low as 0.04%. This is usually considered to be an error.
Studies of blood distribution in various fields
In
order to avoid the influence of "contamination by knowledge", a
Japanese psychologist group published a series of studies, but no
significant differences were found except for Japanese prime ministers. Later, it was reported that significant differences were found not only
for prime ministers, but also for foreign ministers, education
ministers, professional baseball hitters, and soccer players in Japan.
Brain waves and light topography
Kim
and Yi (Seoul University of Venture & Information) measured the
brain waves of 4,636 adults. They reported that type O people were most
stress-resistant.
Popularity
In
Japan, blood types are often used in women's magazines to determine
relationship compatibility with potential or current partners. Blood
type horoscopes are featured in morning television shows and daily newspapers. The blood types of celebrities are often listed in their infoboxes on Japanese Wikipedia.[38]
The four books of a series that describe people's character by blood
type each ranked third, fourth, fifth, and ninth on a list of
best-selling books in Japan in 2008.
One survey showed that at least two-thirds of respondents from
Chinese-speaking East Asian countries and regions believe in an
association between blood types and personality.
In a Japanese survey, more than half of Japanese respondents
stated they were fond of talking about personalities based on blood
types. The research also stated that people in Japan like blood-typical
personality diagnoses, believe there is a relationship between blood
type and personality, and feel its traits apply to themselves to a
certain degree. Two other surveys showed similar results.
Although there is no proven correlation between blood type and personality, many matchmaking
services use it. In this way, it is similar to the use of astrological
signs, which are also popular in Japan. Asking one's blood type is
common in Japan, and people are often surprised when a non-Japanese
person does not know their blood type.
It is common among anime and manga authors to mention their characters' blood types and to give their characters blood types to match their personalities. Some video game characters also have known blood types. Some video game
series also have blood type as a customisable option in their creation
modes.
The Reconstruction Minister Ryu Matsumoto had to resign after abrasive comments towards the governors of Iwate and Miyagi. Afterwards, he partially blamed his behavior on his blood type, saying
"My blood is type B, which means I can be irritable and impetuous, and
my intentions don't always come across."
Blood types are important in South Korea as well. The Korean webcomic A Simple Thinking About Blood Type depicts stereotypes of each blood type and has been adapted as a short anime series in Japan as Ketsuekigata-kun! in 2013 and 2015.
Discrimination
Blood type harassment, called bura-hara (wasei-eigo: a portmanteau of blood and harassment), has been blamed for bullying of children in playgrounds, loss of job opportunities, and the end of relationships.
Discrimination based on blood type has been reported in Japan and
Korea. Examples include questions about blood types during job
interviews despite government warnings against this, children being
split up at school according to their blood type, a national softball
team customizing training to fit each player's blood type, and companies
giving work assignments according to employees' blood type.
However, these examples are contested and deemed. Two
counter-arguments are usually cited. Firstly, there have been no trials
related to blood-type discrimination thus far. Secondly, most Japanese
people do not think blood types determine their personalities, but
rather affect them to some degree.
Vitalism is an idea that living organisms are differentiated
from the non-living by the presence of forces, properties or powers
including those which may not be physical or chemical. Varied forms of
vitalist theories were held in former times and they are now considered pseudoscientific concepts. Where vitalism explicitly invokes a vital principle, that element is often referred to as the "vital spark", "energy", "élan vital" (coined by vitalist Henri Bergson), "vital force", or "vis vitalis", which some equate with the soul. In the 18th and 19th centuries, vitalism was discussed among biologists, between those belonging to the mechanistic school
who felt that the known mechanics of physics would eventually explain
the difference between life and non-life and vitalists who argued that
the processes of life could not be reduced to a mechanistic process.
Vitalist biologists such as Johannes Reinke proposed testablehypotheses
meant to show inadequacies with mechanistic explanations, but their
experiments failed to provide support for vitalism. Biologists now
consider vitalism in this sense to have been refuted by empirical evidence, and hence regard it either as a superseded scientific theory, or as a pseudoscience since the mid-20th century.
Vitalism has a long history in medical philosophies: many traditional healing practices posited that disease results from some imbalance in vital forces.
History
Ancient philosophies
The
notion that bodily functions are due to a vitalistic principle existing
in all living creatures has roots going back at least to ancient Egypt. In Greek philosophy, the Milesian school proposed natural explanations deduced from materialism and mechanism. However, by the time of Lucretius, this account was supplemented, (for example, by the unpredictable clinamen of Epicurus), and in Stoic physics, the pneuma assumed the role of logos. Galen believed the lungs draw pneuma from the air, which the blood communicates throughout the body.
Vitalism is an aspect of Jain philosophy. The Tattvarthsutra by Umaswati states that the universe is made up of six eternal substances: sentient beings or souls (jīva), non-sentient substance or matter (pudgala), principle of motion (dharma), the principle of rest (adharma), space (ākāśa) and time (kāla). The Sarvārthasiddhi by Pujyapada further divides the Jiva into the amount of vitalities of the sense possessed.
Medieval
In Europe, medieval physics was influenced by the idea of pneuma, helping to shape later aether theories.
Early modern
Vitalists included English anatomist Francis Glisson (1597–1677) and the Italian doctor Marcello Malpighi (1628–1694). Caspar Friedrich Wolff (1733–1794) is considered to be the father of epigenesis in embryology,
that is, he marks the point when embryonic development began to be
described in terms of the proliferation of cells rather than the
incarnation of a preformed soul. However, this degree of empirical
observation was not matched by a mechanistic philosophy: in his Theoria Generationis (1759), he tried to explain the emergence of the organism by the actions of a vis essentialis (an organizing, formative force). Carl Reichenbach (1788–1869) later developed the theory of Odic force, a form of life-energy that permeates living things.
In the 17th century, modern science responded to Newton's action at a distance and the mechanism of Cartesian dualism
with vitalist theories: that whereas the chemical transformations
undergone by non-living substances are reversible, so-called "organic"
matter is permanently altered by chemical transformations (such as
cooking).
As worded by Charles Birch and John B. Cobb, "the claims of the vitalists came to the fore again" in the 18th century: "Georg Ernst Stahl's followers were active as were others, such as the physician genius Francis Xavier Bichat of the Hotel Dieu." However, "Bichat moved from the tendency typical of the French vitalistic tradition to progressively free himself from metaphysics in order to combine with hypotheses and theories which accorded to the scientific criteria of physics and chemistry." John Hunter recognised "a 'living principle' in addition to mechanics."
Johann Friedrich Blumenbach was influential in establishing epigenesis in the life sciences in 1781 with his publication of Über den Bildungstrieb und das Zeugungsgeschäfte. Blumenbach cut up freshwater Hydra and established that the removed parts would regenerate. He inferred the presence of a "formative drive" (Bildungstrieb) in living matter. But he pointed out that this name,
like names applied to every other
kind of vital power, of itself, explains nothing: it serves merely to
designate a peculiar power formed by the combination of the mechanical
principle with that which is susceptible of modification.
The synthesis of urea in the early 19th century from inorganic compounds was counterevidence for the vitalist hypothesis that only organisms could make the components of living things.
Jöns Jakob Berzelius, one of the early 19th century founders of modern chemistry, argued that a regulative force must exist within living matter to maintain its functions. Berzelius contended that compounds could be distinguished by whether they required any organisms in their synthesis (organic compounds) or whether they did not (inorganic compounds). Vitalist chemists predicted that organic materials could not be synthesized from inorganic components, but Friedrich Wöhler synthesised urea from inorganic components in 1828. However, contemporary accounts do not support the common belief that vitalism died when Wöhler made urea. This Wöhler Myth,
as historian Peter Ramberg called it, originated from a popular history
of chemistry published in 1931, which, "ignoring all pretense of
historical accuracy, turned Wöhler into a crusader who made attempt
after attempt to synthesize a natural product that would refute vitalism
and lift the veil of ignorance, until 'one afternoon the miracle
happened'".
Between 1833 and 1844, Johannes Peter Müller wrote a book on physiology called Handbuch der Physiologie,
which became the leading textbook in the field for much of the
nineteenth century. The book showed Müller's commitments to vitalism; he
questioned why organic matter differs from inorganic, then proceeded to
chemical analyses of the blood and lymph. He describes in detail the
circulatory, lymphatic, respiratory, digestive, endocrine, nervous, and
sensory systems in a wide variety of animals but explains that the
presence of a soul
makes each organism an indivisible whole. He claimed that the behaviour
of light and sound waves showed that living organisms possessed a
life-energy for which physical laws could never fully account.
Louis Pasteur (1822–1895) after his famous rebuttal of spontaneous generation,
performed several experiments that he felt supported vitalism.
According to Bechtel, Pasteur "fitted fermentation into a more general
programme describing special reactions that only occur in living
organisms. These are irreducibly vital phenomena." Rejecting the claims
of Berzelius, Liebig, Traube
and others that fermentation resulted from chemical agents or catalysts
within cells, Pasteur concluded that fermentation was a "vital action".
20th century
Hans Driesch (1867–1941) interpreted his experiments as showing that life is not run by physicochemical laws. His main argument was that when one cuts up an embryo after its first
division or two, each part grows into a complete adult. Driesch's
reputation as an experimental biologist deteriorated as a result of his
vitalistic theories, which scientists have seen since his time as
pseudoscience. Vitalism is a superseded scientific hypothesis, and the term is sometimes used as a pejorativeepithet. Ernst Mayr (1904–2005) wrote:
It would be ahistorical to ridicule
vitalists. When one reads the writings of one of the leading vitalists
like Driesch one is forced to agree with him that many of the basic
problems of biology simply cannot be solved by a philosophy as that of
Descartes, in which the organism is simply considered a machine... The
logic of the critique of the vitalists was impeccable.
Vitalism has become so disreputable
a belief in the last fifty years that no biologist alive today would
want to be classified as a vitalist. Still, the remnants of vitalist
thinking can be found in the work of Alistair Hardy, Sewall Wright, and Charles Birch, who seem to believe in some sort of nonmaterial principle in organisms.
Other vitalists included Johannes Reinke and Oscar Hertwig. Reinke used the word neovitalism
to describe his work, claiming that it would eventually be verified
through experimentation, and that it was an improvement over the other
vitalistic theories. The work of Reinke influenced Carl Jung.
John Scott Haldane adopted an anti-mechanist approach to biology and an idealist philosophy early on in his career. Haldane saw his work as a vindication of his belief that teleology was an essential concept in biology. His views became widely known with his first book Mechanism, life and personality in 1913. Haldane borrowed arguments from the vitalists to use against mechanism;
however, he was not a vitalist. Haldane treated the organism as
fundamental to biology: "we perceive the organism as a self-regulating
entity", "every effort to analyze it into components that can be reduced
to a mechanical explanation violates this central experience". The work of Haldane was an influence on organicism.
Haldane stated that a purely mechanist interpretation could not account
for the characteristics of life. Haldane wrote a number of books in
which he attempted to show the invalidity of both vitalism and mechanist
approaches to science. Haldane explained:
We must find a different
theoretical basis of biology, based on the observation that all the
phenomena concerned tend towards being so coordinated that they express
what is normal for an adult organism.
By 1931, biologists had "almost unanimously abandoned vitalism as an acknowledged belief."
Contemporary science and engineering sometimes describe emergent processes, in which the properties of a system cannot be fully described in terms of the properties of the constituents. This may be because the properties of the constituents are not fully
understood, or because the interactions between the individual
constituents are important for the behavior of the system.
Whether emergence should be grouped with traditional vitalist concepts is a matter of semantic controversy. According to Emmeche et al. (1997):
On the one hand, many scientists
and philosophers regard emergence as having only a pseudo-scientific
status. On the other hand, new developments in physics, biology,
psychology, and cross-disciplinary fields such as cognitive science,
artificial life, and the study of non-linear dynamical systems have
focused strongly on the high level 'collective behaviour' of complex
systems, which is often said to be truly emergent, and the term is
increasingly used to characterize such systems.
A popular vitalist theory of the 18th century was "animal magnetism", in the theories of Franz Mesmer (1734–1815). However, the use of the (conventional) English term animal magnetism to translate Mesmer's magnétisme animal can be misleading for three reasons:
Mesmer chose his term to clearly distinguish his variant of magnetic force from those referred to, at that time, as mineral magnetism, cosmic magnetism and planetary magnetism.
Mesmer felt that this particular force/power only resided in the bodies of humans and animals.
Mesmer chose the word "animal," for its root meaning (from Latin animus="breath")
specifically to identify his force as a quality that belonged to all
creatures with breath; viz., the animate beings: humans and animals.
Mesmer's ideas became so influential that King Louis XVI of France appointed two commissions to investigate mesmerism; one was led by Joseph-Ignace Guillotin, the other, led by Benjamin Franklin, included Bailly and Lavoisier. The commissioners learned about Mesmeric theory, and saw its patients fall into fits and trances.
In Franklin's garden, a patient was led to each of five trees, one of
which had been "mesmerized"; he hugged each in turn to receive the
"vital fluid," but fainted at the foot of a 'wrong' one. At Lavoisier's
house, four normal cups of water were held before a "sensitive" woman;
the fourth produced convulsions, but she calmly swallowed the mesmerized
contents of a fifth, believing it to be plain water. The commissioners
concluded that "the fluid without imagination is powerless, whereas
imagination without the fluid can produce the effects of the fluid."
Medical philosophies
Vitalism has a long history in medical philosophies: many traditional healing practices posited that disease results from some imbalance in vital forces. One example of a similar notion in Africa is the Yoruba concept of ase. In the European tradition founded by Hippocrates, these vital forces were associated with the four temperaments and humours. Multiple Asian traditions posited an imbalance or blocking of qi or prana.
Amongst unterritorialized traditions such as religions and arts, forms
of vitalism continue to exist as philosophical positions or as memorial
tenets.
Complementary and alternative medicine therapies include energy therapies, associated with vitalism, especially biofield therapies such as therapeutic touch, Reiki, external qi, chakra healing and SHEN therapy. In these therapies, the "subtle energy"
field of a patient is manipulated by a practitioner. The subtle energy
is held to exist beyond the electromagnetic energy produced by the heart
and brain. Beverly Rubik describes the biofield as a "complex, dynamic,
extremely weak EM field within and around the human body...."
The founder of homeopathy, Samuel Hahnemann,
promoted an immaterial, vitalistic view of disease: "...they are solely
spirit-like (dynamic) derangements of the spirit-like power (the vital
principle) that animates the human body." The view of disease as a
dynamic disturbance of the immaterial and dynamic vital force is taught
in many homeopathic colleges and constitutes a fundamental principle for
many contemporary practising homeopaths.
Vitalism has sometimes been criticized as begging the question by inventing a name. Molière had famously parodied this fallacy in Le Malade imaginaire, where a quack "answers" the question of "Why does opium cause sleep?" with "Because of its dormitive virtue (i.e., soporific power)." Thomas Henry Huxley compared vitalism to stating that water is the way it is because of its "aquosity". His grandson Julian Huxley in 1926 compared "vital force" or élan vital to explaining a railroad locomotive's operation by its élan locomotif ("locomotive force").
Another criticism, which predates the fields of organic chemistry and developmental biology, is that vitalists have failed to rule out mechanistic explanations. In 1912, Jacques Loeb published The Mechanistic Conception of Life, in which he described experiments on how a sea urchin could have a pin for its father, as Bertrand Russell put it (Religion and Science). He offered this challenge:
... we must either succeed in producing living matter artificially, or we must find the reasons why this is impossible.
Loeb addressed vitalism more explicitly:
It is, therefore, unwarranted to
continue the statement that in addition to the acceleration of
oxidations the beginning of individual life is determined by the
entrance of a metaphysical "life principle" into the egg; and that death
is determined, aside from the cessation of oxidations, by the departure
of this "principle" from the body. In the case of the evaporation of
water we are satisfied with the explanation given by the kinetic theory
of gases and do not demand that to repeat a well-known jest of Huxley
the disappearance of the "aquosity" be also taken into consideration.
Bechtel states that vitalism "is often viewed as unfalsifiable, and therefore a pernicious metaphysical doctrine." For many scientists, "vitalist" theories were unsatisfactory "holding
positions" on the pathway to mechanistic understanding. In 1967, Francis Crick, the co-discoverer of the structure of DNA,
stated "And so to those of you who may be vitalists I would make this
prophecy: what everyone believed yesterday, and you believe today, only cranks will believe tomorrow."
While many vitalistic theories have in fact been falsified, notably Mesmerism, the pseudoscientific retention of untested and untestable theories continues to this day. Alan Sokal published an analysis of the wide acceptance among professional nurses of "scientific theories" of spiritual healing. Use of a technique called therapeutic touch
was especially reviewed by Sokal, who concluded, "nearly all the
pseudoscientific systems to be examined in this essay are based
philosophically on vitalism" and added that "Mainstream science has
rejected vitalism since at least the 1930s, for a plethora of good
reasons that have only become stronger with time."
Joseph C. Keating, Jr. discusses vitalism's past and present roles in chiropractic and calls vitalism "a form of bio-theology." He further explains that:
Vitalism is that rejected tradition
in biology which proposes that life is sustained and explained by an
unmeasurable, intelligent force or energy. The supposed effects of
vitalism are the manifestations of life itself, which in turn are the
basis for inferring the concept in the first place. This circular reasoning
offers pseudo-explanation, and may deceive us into believing we have
explained some aspect of biology when in fact we have only labeled our
ignorance. 'Explaining an unknown (life) with an unknowable (Innate),'
suggests chiropractor Joseph Donahue, 'is absurd'."
Keating views vitalism as incompatible with scientific thinking:
Chiropractors are not unique in
recognizing a tendency and capacity for self-repair and auto-regulation
of human physiology. But we surely stick out like a sore thumb among
professions which claim to be scientifically based by our unrelenting
commitment to vitalism. So long as we propound the 'One cause, one cure'
rhetoric of Innate, we should expect to be met by ridicule from the
wider health science community. Chiropractors can't have it both ways.
Our theories cannot be both dogmatically held vitalistic constructs and
be scientific at the same time. The purposiveness, consciousness and
rigidity of the Palmers' Innate should be rejected.
Keating also mentions Skinner's viewpoint:
Vitalism has many faces and has sprung up in many areas of scientific inquiry. Psychologist B.F. Skinner,
for example, pointed out the irrationality of attributing behavior to
mental states and traits. Such 'mental way stations,' he argued, amount
to excess theoretical baggage which fails to advance cause-and-effect
explanations by substituting an unfathomable psychology of 'mind'.
According to Williams, "[t]oday, vitalism is one of the ideas that
form the basis for many pseudoscientific health systems that claim that
illnesses are caused by a disturbance or imbalance of the body's vital
force." "Vitalists claim to be scientific, but in fact they reject the
scientific method with its basic postulates of cause and effect and of
provability. They often regard subjective experience to be more valid
than objective material reality."
Victor Stenger states that the term "bioenergetics" "is applied in biochemistry to refer to the readily measurable exchanges of energy
within organisms, and between organisms and the environment, which
occur by normal physical and chemical processes. This is not, however,
what the new vitalists have in mind. They imagine the bioenergetic field as a holistic living force that goes beyond reductionist physics and chemistry."
Such a field is sometimes explained as electromagnetic, though some advocates also make confused appeals to quantum physics. Joanne Stefanatos states that "The principles of energy medicine originate in quantum physics." Stenger offers several explanations as to why this line of reasoning may be
misplaced. He explains that energy exists in discrete packets called
quanta. Energy fields are composed of their component parts and so only
exist when quanta are present. Therefore, energy fields are not
holistic, but are rather a system of discrete parts that must obey the
laws of physics. This also means that energy fields are not
instantaneous. These facts of quantum physics place limitations on the
infinite, continuous field that is used by some theorists to describe
so-called "human energy fields". Stenger continues, explaining that the effects of EM forces have been
measured by physicists as accurately as one part in a billion and there
is yet to be any evidence that living organisms emit a unique field.
Vitalistic thinking has been identified in the naive biological
theories of children: "Recent experimental results show that a majority
of preschoolers tend to choose vitalistic explanations as most
plausible. Vitalism, together with other forms of intermediate
causality, constitute unique causal devices for naive biology as a core
domain of thought."
Acetylcholine (ACh) is an organic compound that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Parts in the body that use or are affected by acetylcholine are referred to as cholinergic.
Acetylcholine is the neurotransmitter used at the neuromuscular junction. In other words, it is the chemical that motor neurons
of the nervous system release in order to activate muscles. This
property means that drugs that affect cholinergic systems can have very
dangerous effects ranging from paralysis to convulsions. Acetylcholine is also a neurotransmitter in the autonomic nervous system, both as an internal transmitter for both the sympathetic and the parasympathetic nervous system, and as the final product released by the parasympathetic nervous system. Acetylcholine is the primary neurotransmitter of the parasympathetic nervous system.
In the brain, acetylcholine functions as a neurotransmitter and as a neuromodulator. The brain contains a number of cholinergic areas, each with distinct functions; such as playing an important role in arousal, attention, memory and motivation. Acetylcholine has also been found in cells of non-neural origins as
well as microbes. Recently, enzymes related to its synthesis,
degradation and cellular uptake have been traced back to early origins
of unicellular eukaryotes. The protist pathogens Acanthamoeba spp. have shown evidence of the presence of ACh, which provides growth and proliferative signals via a membrane-located M1-muscarinic receptor homolog.
Partly because of acetylcholine's muscle-activating function, but
also because of its functions in the autonomic nervous system and
brain, many important drugs exert their effects by altering cholinergic
transmission. Numerous venoms and toxins produced by plants, animals, and bacteria, as well as chemical nerve agents such as sarin,
cause harm by inactivating or hyperactivating muscles through their
influences on the neuromuscular junction. Drugs that act on muscarinic acetylcholine receptors, such as atropine,
can be poisonous in large quantities, but in smaller doses they are
commonly used to treat certain heart conditions and eye problems. Scopolamine, or diphenhydramine, which also act mainly on muscarinic receptors in an inhibitory fashion in the brain (especially the M1 receptor) can cause delirium, hallucinations, and amnesia through receptor antagonism at these sites. So far as of 2016, only the M1 receptor subtype has been implicated in anticholinergic delirium. The addictive qualities of nicotine are derived from its effects on nicotinic acetylcholine receptors in the brain.
Chemistry
Acetylcholine is a choline molecule that has been acetylated at the oxygen atom. Because of the charged ammonium
group, acetylcholine does not penetrate lipid membranes. Because of
this, when the molecule is introduced externally, it remains in the
extracellular space and at present it is considered that the molecule
does not pass through the blood–brain barrier.
Biochemistry
Acetylcholine is synthesized in certain neurons by the enzymecholine acetyltransferase from the compounds choline and acetyl-CoA.
Cholinergic neurons are capable of producing ACh. An example of a
central cholinergic area is the nucleus basalis of Meynert in the basal
forebrain. The enzyme acetylcholinesterase converts acetylcholine into the inactive metabolitescholine and acetate.
This enzyme is abundant in the synaptic cleft, and its role in rapidly
clearing free acetylcholine from the synapse is essential for proper
muscle function. Certain neurotoxins work by inhibiting acetylcholinesterase, thus leading to excess acetylcholine at the neuromuscular junction, causing paralysis of the muscles needed for breathing and stopping the beating of the heart.
Acetylcholine processing in a synapse. After release acetylcholine is broken down by the enzyme acetylcholinesterase.
Like many other biologically active substances, acetylcholine exerts its effects by binding to and activating receptors located on the surface of cells. There are two main classes of acetylcholine receptor, nicotinic and muscarinic. They are named for chemicals that can selectively activate each type of receptor without activating the other: muscarine is a compound found in the mushroom Amanita muscaria; nicotine is found in tobacco.
Nicotinic acetylcholine receptors are ligand-gated ion channels permeable to sodium, potassium, and calcium
ions. In other words, they are ion channels embedded in cell membranes,
capable of switching from a closed to an open state when acetylcholine
binds to them; in the open state they allow ions to pass through.
Nicotinic receptors come in two main types, known as muscle-type and
neuronal-type. The muscle-type can be selectively blocked by curare, the neuronal-type by hexamethonium.
The main location of muscle-type receptors is on muscle cells, as
described in more detail below. Neuronal-type receptors are located in
autonomic ganglia (both sympathetic and parasympathetic), and in the
central nervous system.
Muscarinic acetylcholine receptors
have a more complex mechanism, and affect target cells over a longer
time frame. In mammals, five subtypes of muscarinic receptors have been
identified, labeled M1 through M5. All of them function as G protein-coupled receptors, meaning that they exert their effects via a second messenger system. The M1, M3, and M5 subtypes are Gq-coupled; they increase intracellular levels of IP3 and calcium by activating phospholipase C. Their effect on target cells is usually excitatory. The M2 and M4 subtypes are Gi/Go-coupled; they decrease intracellular levels of cAMP by inhibiting adenylate cyclase.
Their effect on target cells is usually inhibitory. Muscarinic
acetylcholine receptors are found in both the central nervous system and
the peripheral nervous system of the heart, lungs, upper
gastrointestinal tract, and sweat glands.
Neuromuscular junction
Muscles
contract when they receive signals from motor neurons. The
neuromuscular junction is the site of the signal exchange. The steps of
this process in vertebrates occur as follows: (1) The action potential
reaches the axon terminal. (2) Calcium ions flow into the axon terminal.
(3) Acetylcholine is released into the synaptic cleft.
(4) Acetylcholine binds to postsynaptic receptors. (5) This binding
causes ion channels to open and allows sodium ions to flow into the
muscle cell. (6) The flow of sodium ions across the membrane into the
muscle cell generates an action potential which induces muscle
contraction. Labels: A: Motor neuron axon B: Axon terminal C: Synaptic
cleft D: Muscle cell E: Part of a Myofibril
Acetylcholine is the substance the nervous system uses to activate skeletal muscles, a kind of striated muscle. These are the muscles used for all types of voluntary movement, in contrast to smooth muscle tissue,
which is involved in a range of involuntary activities such as movement
of food through the gastrointestinal tract and constriction of blood
vessels. Skeletal muscles are directly controlled by motor neurons located in the spinal cord or, in a few cases, the brainstem. These motor neurons send their axons through motor nerves, from which they emerge to connect to muscle fibers at a special type of synapse called the neuromuscular junction.
When a motor neuron generates an action potential,
it travels rapidly along the nerve until it reaches the neuromuscular
junction, where it initiates an electrochemical process that causes
acetylcholine to be released into the space between the presynaptic
terminal and the muscle fiber. The acetylcholine molecules then bind to
nicotinic ion-channel receptors on the muscle cell membrane, causing the
ion channels to open. Sodium ions then flow into the muscle cell,
initiating a sequence of steps that finally produce muscle contraction.
Factors that decrease release of acetylcholine (and thereby affecting P-type calcium channels):
The autonomic nervous system controls a wide range of involuntary and unconscious body functions. Its main branches are the sympathetic nervous system and parasympathetic nervous system.
Broadly speaking, the function of the sympathetic nervous system is to
mobilize the body for action; the phrase often invoked to describe it is
fight-or-flight.
The function of the parasympathetic nervous system is to put the body
in a state conducive to rest, regeneration, digestion, and reproduction;
the phrase often invoked to describe it is "rest and digest" or "feed
and breed". Both of these aforementioned systems use acetylcholine, but
in different ways.
At a schematic level, the sympathetic and parasympathetic nervous
systems are both organized in essentially the same way: preganglionic
neurons in the central nervous system send projections to neurons
located in autonomic ganglia, which send output projections to virtually
every tissue of the body. In both branches the internal connections,
the projections from the central nervous system to the autonomic
ganglia, use acetylcholine as a neurotransmitter to innervate (or
excite) ganglia neurons. In the parasympathetic nervous system the
output connections, the projections from ganglion neurons to tissues
that do not belong to the nervous system, also release acetylcholine but
act on muscarinic receptors. In the sympathetic nervous system the
output connections mainly release noradrenaline, although acetylcholine is released at a few points, such as the sudomotor innervation of the sweat glands.
In the central nervous system, ACh has a variety of effects on plasticity, arousal and reward. ACh has an important role in the enhancement of alertness when we wake up, in sustaining attention and in learning and memory.
Damage to the cholinergic (acetylcholine-producing) system in the
brain has been shown to be associated with the memory deficits
associated with Alzheimer's disease. ACh has also been shown to promote REM sleep.
In addition, ACh acts as an important internal transmitter in the striatum, which is part of the basal ganglia. It is released by cholinergic interneurons.
In humans, non-human primates and rodents, these interneurons respond
to salient environmental stimuli with responses that are temporally
aligned with the responses of dopaminergic neurons of the substantia nigra.
Memory
Acetylcholine has been implicated in learning and memory in several ways. The anticholinergic drug scopolamine impairs acquisition of new information in humans and animals. In animals, disruption of the supply of acetylcholine to the neocortex impairs the learning of simple discrimination tasks, comparable to the acquisition of factual information and disruption of the supply of acetylcholine to the hippocampus and adjacent cortical areas produces forgetfulness, comparable to anterograde amnesia in humans.
Diseases and disorders
Myasthenia gravis
The disease myasthenia gravis, characterized by muscle weakness and fatigue, occurs when the body inappropriately produces antibodies against acetylcholine nicotinic receptors, and thus inhibits proper acetylcholine signal transmission. Over time, the motor end plate is destroyed. Drugs that competitively inhibit acetylcholinesterase (e.g., neostigmine, physostigmine, or primarily pyridostigmine) are effective in treating the symptoms of this disorder. They allow endogenously released acetylcholine more time to interact
with its respective receptor before being inactivated by
acetylcholinesterase in the synaptic cleft (the space between nerve and muscle).
Pharmacology
Blocking,
hindering or mimicking the action of acetylcholine has many uses in
medicine. Drugs acting on the acetylcholine system are either agonists
to the receptors, stimulating the system, or antagonists, inhibiting it.
Acetylcholine receptor agonists and antagonists can either have an
effect directly on the receptors or exert their effects indirectly,
e.g., by affecting the enzyme acetylcholinesterase, which degrades the receptor ligand. Agonists increase the level of receptor activation; antagonists reduce it.
Acetylcholine itself does not have therapeutic value as a drug
for intravenous administration because of its multi-faceted action
(non-selective) and rapid inactivation by cholinesterase. However, it is
used in the form of eye drops to cause constriction of the pupil during
cataract surgery, which facilitates quick post-operational recovery.
Nicotine binds to and activates nicotinic acetylcholine receptors, mimicking the effect of acetylcholine at these receptors. ACh opens a Na+channel upon binding so that Na+
flows into the cell. This causes a depolarization, and results in an
excitatory post-synaptic potential. Thus, ACh is excitatory on skeletal
muscle; the electrical response is fast and short-lived. Curares are arrow poisons, which act at nicotinic receptors and have been used to develop clinically useful therapies.
Many ACh receptor agonists work indirectly by inhibiting the enzyme acetylcholinesterase.
The resulting accumulation of acetylcholine causes continuous
stimulation of the muscles, glands, and central nervous system, which
can result in fatal convulsions if the dose is high.
They are examples of enzyme inhibitors, and increase the action of acetylcholine by delaying its degradation; some have been used as nerve agents (Sarin and VX nerve gas) or pesticides (organophosphates and the carbamates).
Many toxins and venoms produced by plants and animals also contain
cholinesterase inhibitors. In clinical use, they are administered in low
doses to reverse the action of muscle relaxants, to treat myasthenia gravis, and to treat symptoms of Alzheimer's disease (rivastigmine, which increases cholinergic activity in the brain).
Synthesis inhibitors
Organic mercurial compounds, such as methylmercury, have a high affinity for sulfhydryl groups,
which causes dysfunction of the enzyme choline acetyltransferase. This
inhibition may lead to acetylcholine deficiency, and can have
consequences on motor function.
Release inhibitors
Botulinum toxin (Botox) acts by suppressing the release of acetylcholine, whereas the venom from a black widow spider (alpha-latrotoxin) has the reverse effect. ACh inhibition causes paralysis. When bitten by a black widow spider, one experiences the wastage of ACh supplies and the muscles begin to contract. If and when the supply is depleted, paralysis occurs.
Photopharmacological agents
Photopharmacology
is an emerging field that uses light to control the activity of
biologically active compounds with high spatial and temporal precision.
Recent advances have applied this approach to the cholinergic system,
including photoactivatable agonists and antagonists of muscarinic and
nicotinic acetylcholine receptors, as well as light-sensitive
acetylcholinesterase inhibitors, that enable reversible and targeted
modulation of cholinergic signaling upon irradiation. These
light-regulated compounds, based on either photolabile protecting groups
("caged" ligands) or photoisomerizable scaffolds, offer unprecedented
control over acetylcholine-mediated processes and represent promising
tools for both basic research and potential therapeutic applications.
Comparative biology and evolution
Acetylcholine is used by organisms in all domains of life for a variety of purposes. It is believed that choline, a precursor to acetylcholine, was used by single celled organisms billions of years ago for synthesizing cell membrane phospholipids. Following the evolution of choline transporters, the abundance of
intracellular choline paved the way for choline to become incorporated
into other synthetic pathways, including acetylcholine production.
Acetylcholine is used by bacteria, fungi, and a variety of other
animals. Many of the uses of acetylcholine rely on its action on ion
channels via GPCRs like membrane proteins.
The two major types of acetylcholine receptors, muscarinic and
nicotinic receptors, have convergently evolved to be responsive to
acetylcholine. This means that rather than having evolved from a common
homolog, these receptors evolved from separate receptor families. It is
estimated that the nicotinic receptor family dates back longer than 2.5 billion years. Likewise, muscarinic receptors are thought to have diverged from other
GPCRs at least 0.5 billion years ago. Both of these receptor groups have
evolved numerous subtypes with unique ligand affinities and signaling
mechanisms. The diversity of the receptor types enables acetylcholine to
create varying responses depending on which receptor types are
activated, and allow for acetylcholine to dynamically regulate
physiological processes. ACh receptors are related to 5-HT3 (serotonin), GABA, and Glycine receptors, both in sequence and structure, strongly suggesting that they have a common evolutionary origin.
History
In 1867, Adolf von Baeyer resolved the structures of choline and acetylcholine and synthesized them both, referring to the latter as acetylneurin in the study. Choline is a precursor for acetylcholine. Acetylcholine was first noted to be biologically active in 1906, when Reid Hunt (1870–1948) and René de M. Taveau found that it decreased blood pressure in exceptionally tiny doses.This was after Frederick Walker Mott and William Dobinson Halliburton noted in 1899 that choline injections decreased the blood pressure of animals.
In 1914, Arthur J. Ewins was the first to extract acetylcholine
from nature. He identified it as the blood pressure-decreasing
contaminant from some Claviceps purpureaergot extracts, by the request of Henry Hallett Dale. Later in 1914, Dale outlined the effects of acetylcholine at various
types of peripheral synapses and also noted that it lowered the blood
pressure of cats via subcutaneous injections even at doses of one nanogram.
The concept of neurotransmitters was unknown until 1921, when Otto Loewi noted that the vagus nerve secreted a substance that inhibited the heart muscle whilst working as a professor in the University of Graz. He named it vagusstoff ("vagus substance"), noted it to be a structural analog of choline and suspected it to be acetylcholine. In 1926, Loewi and E. Navratil deduced that the compound is probably
acetylcholine, as vagusstoff and synthetic acetylcholine lost their
activity in a similar manner when in contact with tissue lysates that contained acetylcholine-degrading enzymes (now known to be cholinesterases). This conclusion was accepted widely. Later studies confirmed the function of acetylcholine as a neurotransmitter.
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