Nature or Nurture?

by endlesspsych

Nature or Nurture is one of those debates in psychology that never really seems to go away, at least in the public imagination, is our behaviour determined more by our genes or by our enviroment? Often most people will say, when asked, that of course both play an important role and neither one should be dismissed over the other.

I’d contend, in agreement with Stephen Pinkers’ thesis in the Blank Slate, that the dominant intellectual position is not that which is  stated but is more based upon the following:

Pinker argues that modern science has challenged three “linked dogmas” that constitute the dominant view of human nature in intellectual life:

  • the ghost in the machine (each of us has a soul that makes choices free from biology)
  • That is to say that while some (lay) people claim to accept that ‘some’ variation in behaviour is down to genes they distrust or doubt any evidence to suggest that genetic determinism accounts for anything more than the slightest changes and variations.  While the “dogmas” listed above no doubt represent extreme views in this area it is my contention they do summarize a lot of the reasons why people reject notions of determinism in favour of a reality seemingly based more in social constructionism. My view can be summarised as that below:

    Our genetic code acts like a computer program which determines not only our phenotype, but our extended phenotype, in this way the role of enviroment (or nurture) is one of compiler not of coder.

    It’s a fairly strong determinist position – essentially holding that nurture is a product of nature or rather an interaction of genes with enviroment. Although it of course holds the tantalising (and probably flawed in a utopian sense ideal) that perhaps, just perhaps, we could tailor our enviroment to ensure our extended phenotype is expressed only in ways we want it to.  Which is one of the main reasons people seem to oppose the idea of human nature – perhaps because they think it will inevitably lead to “nasty, brutish and shorte” lifes.

    The BBC’s latest program – the secret life of twins (along with ongoing discussions about this very issue I have had) has prompted my to write this blog post and to present some of the evidence, from twin studies, that suggests the level to which how we are and who we are is determined by our genetic code.

    The Minnesota centre for twin and family studies comprises of two studies that demonstrate how the issue of nature or nurture can be explored: the Minnesota Twin Family Study (MTFS) and the Sibling Interaction and Behavior Study (SIBS). Both projects are longitudinal research studies including twins, siblings, and parents. Studying twins (identical and fraternal) allows us to see what is influenced by our genes and what is influenced by our enviroment. The rationale behind the SIBS study is to measure how much genes/enviroment influence behaviour by looking at adoptive families – families that share the same enviroment but not the same genes. Both these types of studies can be used to determine how much genes determine our behaviour and how much is down to the enviroment.

    Identical twins feel a great bond with each other and in cases where they have been separated until adulthood often remark that they feel as if they have known each other for their whole lives. Testing has confirmed that identical twins who have been separated at birth are eerily similar (although not identical) in many respects. They are similar in verbal, mathematical and general intelligence, in their degree of life satisfaction, big five personality traits. They hold similar issues on political and social issues such as the death penalty, religion and modern music. They even resemble each other in how their lives have run their course outside of paper and pen tests in the lab in such activities as television watching, gambling, risk taking and divorce. If we go further down the rabbit hole we see that they share certain idiosyncracies like giggling incessantly, giving interminable answers to simple questions, dipping buttered toast in coffee and various other individual traits for which we would assume the genes played little or no part.  (Not that I am saying that there is a gene for giggling incessently but it seems that in some cases there may be a section of genetic code that makes someone likely to do such a thing.).

    For example: A version of the gene IGF2R is associated with high intelligence, a longer than average version of the D4DR dopamine receptor with thrill seeking and there are many more.

    A conventional summary is that about half the variation in intelligence, personality and life outcomes is heritable meaning that around half the variation is due to genes leaving the other half to the enviroment. However it could be more or it could be less then this as measurement techniques are not 100% infalliable.

    Although this does at least give me some license to venture that for all our suppossed incompatiable cultural differences (most of which I hold to be cosmetic) we are all the same homo-sapiens underneath and as much as we protest we probably all think a lot more alike then those who hold different cultures produce different people like to think.