Genetics vs Environment in Human Development

In this essay I will discuss the extent to which hereditary factors influence human development, and whether our environment (observations and perceptions) play a role in individualistic growth. I will analyse epigenesis, by discussing the complex interactions between genes and environment

Nature refers to the theory that genetic predispositions impact human traits and nurture involves the idea that we are a product of our own environments. The controversial debate of nature vs nurture was first invented by Francis Galton in the late 19th Century; convinced intellectual ability was largely inherited, this thesis was the basis on which he suggested ‘pure breeding’. Met with criticism due to its social and political implications, it is believed that this was followed by the eugenics society’s encouragement of sterilisation (however the formation of such immigration policies led to the discrimination of black and Asian ethnic groups). This essay will infer from the debate of nature vs nurture, particularly the evaluation of the involvement genetics have on human development(specifically IQ and personality), I will argue that whilst to some extent genes contribute to the development of an individual, environmental factors also play a key role. I will evaluate the claim by analysing key studies and concepts (such as twin and adoption studies) on either side of the debate, as well as the contributing my viewpoint when addressing the concept of this statement.

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Nativism is an extreme hereditary stance taken on this debate; it involves the idea that humans are products of evolution. It uses heritability estimate( statistical measure which shows the extent to which genetic factors cause individual differences in complex traits) and genetic variance (contribution of different versions of genomes have on individual differences) .Key examples involve Chomsky’s (1965) proposal of universal language theory, put forward after his criticism of Skinner’s account of language acquisition. It involves the concept of innate biological grammatical groups such as verb category facilitated language development in adults. Another example, Freud’s (1905) theory of aggression, Thanatos suggested humans have a death drives involving self-destructive tendencies. Characteristics which are not visible at birth but develop later in life are believed to be ‘turned on’ using innate biological devices. On the other hand, empiricism takes an extreme nurture take. John Locke proposed humans are born as ‘blank slates’ and implies we have no mental content at birth; all knowledge comes from experience or what we perceive our surroundings as. Bandura (1977) Bobo doll experiment suggested observational learning is key on our development, specifically, how children learn to imitate the behaviour they see in adults. Another behaviourist, Skinner (1957) stated language is learnt and acquired based on behaviour and is reinforced when words are associated with meanings.

Firstly, evidence suggests IQ has substantial genetic basis. Twin studies compare correlation between monozygotic twins (MZ) and dizygotic twins (DZ). MZ twins share 100% of their genes whereas DZ twins share 50%. Therefore if MZ and DZ twins score the same it suggests nature does not play a large role on behaviour, but if scores are different, it implies nature is a key contributor as shared environment is not causing this, so genetic differences must be the reason. Research by Plomin and DeFries (1998) found a higher correlation in similarity between identical twins on cognitive tasks (spatial/verbal ability) than fraternal twins. This suggests there is strong genetic basis for cognitive abilities, leaning towards the nature side of the debate. Adoption studies show impact of nurture on children, who are raised by parents who are not their biological related. Plomin and DeFries (1998) also found adoption studies provided evidence for strong genetic influence in cognitive skills. Results demonstrate a higher correlation in similarity between adopted children and their biological parents, rather than their adoptive family. Further supporting the notion of substantial genetic influence on cognitive ability and IQ.

Research by Tryon (1934) trained rats on a maze. Interbred rats which made most, and fewest maze mistakes were looked at. Over successive generations, bred rats that were either ‘bright’, solved the maze with few errors, or ‘dull’ made many errors. Over successive generations the ‘dull’ and ‘bright’ groups gradually separated so was little overlap. This demonstrates some elements of intelligence are genetically determined. Likely to be a polygenic trait (multiple genes involved) since generations of breeding required for groups to separate. Animal studies are commonly used, and findings are extrapolated to human development. However, with animal observations there is a lack of scientific generalisability. On the other hand, Cooper and Zubeck (1958) investigated whether environment in which the rats were raised influenced maze learning. Performance of ‘dull’ rats improved by being reared in an enriched environment. Performance of ‘bright’ rats reduced if raised in a restricted environment. Experience ‘overcomes’ genetic influence. This research implies that whilst genes have a string influence on our cognitive abilities, the environment in which we are raised must support abilities and be cognitively stimulating for good performance. Overall, such studies suggest intelligence is not 100% inheritable, moreover cognitive development is also largely dependent on resources and environmental interactions.

'Personality is the dynamic organization within the individual of those psychophysical systems that determine his characteristics behaviour and thought' (Allport, 1961). It is believed that environmental influences play crucial roles in the functioning of the personality system, defining conditions of evolvement, they shape an array of skills, values, attitudes; they also provide the factual forms of trait expression. However, the environment also has a direct relation to personality traits, because characteristic adaptations are always involved in expression. An example, interpersonal traits are often inferred from communicating with others; the environment also operates at a much more direct level. Parenting has important long-term consequences for the development of characteristic adaptations, including, the lifelong relationship between parent and child (internal template provides a representation of what future relationships should be like). Other aspects of the environment are also significant influences on characteristic changes, including peers, education, religion etc. Research by Cosmides and Tooby (2009) provide an evolutionary perspective and suggest biological machines are calibrated to the environments in which they evolved, and they embody information about recurring properties of these worlds. They found data supported theory of evolutionary basis to personality traits e.g. anger. Personality traits, like temperaments, are endogenous dispositions that follow intrinsic paths of development, independent of environmental influences. Freuds psychodynamic approach assumes there is an interaction between innate instincts and parental influences. The tripartite theory of personality by Freud (1923) brings forward the notion that the psyche is made up of the id, superego and ego. These traits predispose to act in a certain way, regardless of the situation also, it is presumed that individuals differ in traits due to genetic differences. Eysenck (1952,) proposed theory of personality based on biological factors, and argued that individuals inherit a type of nervous system that affects their ability to learn and adapt to the environment. Furthermore, he developed an extraversion/introversion scale. Eysenck’s theory argues biological predispositions towards certain personality traits combine with conditioning and socialisation during childhood, creating our personality. This interactionist approach may therefore be more valid than either an environmental or biological theory alone.

Adorno et al. (1950) theory of authoritarian personality suggests prejudice is brought on by personality type. Authoritarianism was measured on a fascism scale; personality traits predisposed some individuals to be highly sensitive to totalitarian/antidemocratic ideas and therefore prone to be extremely prejudicial, they usually believe in complete submission to authority as well as hostility to minority(inferior) groups. It is suggested that individuals who experience harsh parenting and conditional love, built resentment towards their parents/upbringing and this was later displaced onto groups society may label as inferior, making them more likely to become authoritarian. Whilst there are political implications with this theory, it supports the nurture side of the debate, implying the environment and upbringing individuals receive have a strong influence on personality types, and behaviour towards other groups of society.

Based on research and analysis above, it appears evidence collectively presents an overall interactionist approach. This paper argued that whilst there is strong evidence suggesting genetics have significant influence, there is contrary research presenting interactions with the environment as substantially effective in our development; the studies looked at above are vital in illustrating this point. Neither IQ or personality traits are 100% heritable, and continuously develop if the environment in which we are brought up in is cognitively stimulating, as well enriching. Whilst some data is inferred from observation of animals, it suggests genes are not solely responsible in human development.

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