Biological determinism, also known asgenetic determinism,[1] is the belief that human behaviour is directly controlled by an individual'sgenes or some component of theirphysiology, generally at the expense of the role of the environment, whether in embryonic development or in learning.[2]Genetic reductionism is a similar concept, but it is distinct from genetic determinism in that the former refers to the level of understanding, while the latter refers to the supposed causal role of genes.[3] Biological determinism has been associated with movements in science and society includingeugenics,scientific racism, and the debates around theheritability of IQ,[4] the basis ofsexual orientation,[5] and evolutionary foundations of cooperation insociobiology.[6]
In 1892, the German evolutionary biologistAugust Weismann proposed in hisgerm plasm theory that heritable information is transmitted only viagerm cells, which he thought contained determinants (genes). The English polymathFrancis Galton, supposing that undesirable traits such asclub foot andcriminality were inherited, advocated eugenics, aiming to prevent supposedly defective people from breeding. The American physicianSamuel George Morton and the French physicianPaul Broca attempted to relate the cranial capacity (internal skull volume) to skin colour, intending to show thatwhite people were superior. Other workers such as the American psychologistsH. H. Goddard andRobert Yerkes attempted tomeasure people's intelligence and to show that the resulting scores were heritable, again to demonstrate the supposed superiority of people with white skin.[4]
Galton popularized the phrasenature and nurture, later often used to characterize the heated debate over whether genes or the environment determined human behaviour. Scientists such as behavioural geneticists now see it as obvious that both factors are essential, and that they are intertwined, especially through the mechanisms ofepigenetics.[7][8] The American biologistE. O. Wilson, who founded the discipline of sociobiology based on observations of animals such associal insects, controversially suggested that its explanations of social behaviour might apply to humans.[6]
In 1892, the Austrian biologistAugust Weismann proposed that multicellular organisms consist of two separate types of cell:somatic cells, which carry out the body's ordinary functions, andgerm cells, which transmit heritable information. He called the material that carried the information, now identified asDNA, thegerm plasm, and individual components of it, now calledgenes, determinants which controlled the organism.[9] Weismann argued that there is a one-way transfer of information from the germ cells to somatic cells, so that nothing acquired by the body during an organism's life can affect the germ plasm and the next generation. This effectively denied thatLamarckism (inheritance of acquired characteristics) was a possible mechanism of evolution.[10] The modern equivalent of the theory, expressed at molecular rather than cellular level, is thecentral dogma of molecular biology.[11]
Early ideas of biological determinism centred on the inheritance of undesirable traits, whether physical such asclub foot orcleft palate, or psychological such asalcoholism,bipolar disorder andcriminality. The belief that such traits were inherited led to an attempt to solve the problem with theeugenics movement. This was led by a follower ofDarwin,Francis Galton (1822–1911), who advocated forcibly reducing breeding among people with those traits. By the 1920s, many U.S. states enacted laws permitting the compulsorysterilization of people considered genetically unfit, including inmates ofprisons andpsychiatric hospitals. This was followed by similar laws in Germany, and throughout the Western world, in the 1930s.[13][4][14]
Under the influence of determinist beliefs, the AmericancraniologistSamuel George Morton (1799–1851), and later the French anthropologistPaul Broca (1824–1880), attempted to measure the cranial capacities (internal skull volumes) of people of different skin colours, intending to show that whites were superior to the rest, with larger brains. All the supposed proofs from such studies were invalidated by methodological flaws. The results were used to justifyslavery, and to opposewomen's suffrage.[4]
Alfred Binet (1857–1911) designed tests specifically to measure performance, not innate ability. From the late 19th century, the American school, led by researchers such asH. H. Goddard (1866–1957),Lewis Terman (1877–1956), andRobert Yerkes (1876–1956), transformed these tests into tools for measuring inherited mental ability. They attempted to measure people's intelligence withIQ tests, to demonstrate that the resulting scores wereheritable, and so to conclude thatpeople with white skin were superior to the rest. It proved impossible to design culture-independent tests and to carry out testing in a fair way given that people came from different backgrounds, or were newly arrived immigrants, or were illiterate. The results were used to opposeimmigration of people from southern and eastern Europe to the USA.[4]
Human sexual orientation, which ranges overa continuum from exclusive attraction to the opposite sex to exclusive attraction to the same sex,[15] is caused by the interplay of genetic andenvironmental influences.[16] There is considerably more evidence forbiological causes of sexual orientation than social factors, especially for males.[15][17]
Sociobiology emerged withE. O. Wilson's 1975 bookSociobiology: The New Synthesis.[6] The existence of a putativealtruism gene has been debated; the evolutionary biologistW. D. Hamilton proposed "genes underlying altruism" in 1964,[18][19] while the biologist Graham J. Thompson and colleagues identified the genesOXTR,CD38,COMT,DRD4,DRD5,IGF2,GABRB2 as candidates "affecting altruism".[20] The geneticistSteve Jones argues that altruistic behaviour like "loving our neighbour" is built into the human genome, with the proviso that neighbour means member of "our tribe", someone who shares many genes with the altruist, and that the behaviour can thus be explained bykin selection.[21] Evolutionary biologists such as Jones have argued that genes that did not lead to selfish behaviour would die out compared to genes that did, because the selfish genes would favour themselves. However, the mathematician George Constable and colleagues have argued that altruism can be anevolutionarily stable strategy, making organisms better able to survive random catastrophes.[22][23]
The belief in biological determinism was matched in the 20th century by ablank slate denial of any possible influence of genes on human behaviour, leading toa long and heated debate about "nature and nurture". By the 21st century, many scientists had come to feel that the dichotomy made no sense. They noted that genes are expressed within an environment, in particular that ofprenatal development, and that gene expression is continuously influenced by the environment through mechanisms such asepigenetics.[24][25][26] Epigenetics provides evidence that human behaviours orphysiology can be decided by interactions between genes and environments.[27] For example,monozygotic twins usually have exactly identicalgenomes. Scientists have focused on comparison studies of such twins for evaluating theheritability of genes and the roles of epigenetics in divergences and similarities between monozygotic twins, and have found that epigenetics plays an important part in human behaviours, including the stress response.[28][29]
I will use here 'biology' and 'genetics' ... interchangeably ... because this is the way they are used in most of the literature I analyze here ... Critics accuse those who use biology to explain every possible human trait of presupposing the truth of biological or genetic determinism.
The idea that an individual's personality or behaviour is caused by their particular genetic endowment, rather than by social or cultural factors—by nature rather than nurture.
Where Weismann would say that it is impossible for changes acquired during an organism's lifetime to feed back onto transmissible traits in the germ line, the CDMB now added that it was impossible for information encoded in proteins to feed back and affect genetic information in any form whatsoever, which was essentially a molecular recasting of the Weismann barrier.
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