Nature Versus Nurture: Really?

As it turns out, we are products of our genes and our environment.  No duh!  Debate over!  Right?  Nope!   I had assumed that it was commonly accepted that genes matter.  I had no idea that acknowledging this reality was in a sense sacrilegious to some.  Although Pinker made clear the debate, I suspected that perhaps this was an esoteric intellectual war of words limited to philosophical types with high brow notions about macro economic models and so on.  But, I became more aware of the lingering embers of environmental determinism as a result of a firestorm that erupted last week regarding an essay written by an environmental advocacy group spread about on Twitter and a subsequent article posted in the Huffington Post.  These articles essentially minimized genetic determinism in major health issues due to the failure of the Human Genome Project to isolate specific genes responsible for specific illnesses.  Out with the genes – in with the environment the proponents celebrated.   Environmental determinists pounced on the absence of evidence as if it were evidence of absence (Carmichael, 2010).  As it turns out, genes are really complex and diseases are influenced, it seems, by gene cohorts rather than any one specific gene.  I am less familiar with the research regarding genetic influence on disease but the tone of the banter reminded me of the debate about human nature detailed by Pinker.

 

I have discussed in several recent posts the impact of genes on important issues such as personality, adaptive functioning, and even political perspectives.  The psychologist Eric Turkheimer pulled together the unusually robust evidence from extensive studies of twins (fraternal and identical) reared together and apart as well as studies of adopted children relative to biological children and concluded that there are three important laws that help explain the development of personality characteristics and intelligence.   The three laws are as follows:

 

  1. All Human traits are heritable;
  2. The effect of being raised in the same family is smaller than the effect of the genes; and
  3. A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families.

 

These laws are best summarized based on current research from behavioral genetics as follows:

 

  1. Heredity accounts for about 50% of the variance in the adaptive functioning outcomes of children.
  2. The home environment, as it is influenced by parents, accounts for 0 to 10%, and
  3. The child’s peer group accounts for the remainder (40-50%)  (Pinker, 2002).

 

Corresponding laws regarding the variants affecting diseases are perhaps unclear at this time.  But denial of genetic influence is much like the denial of the heliocentric theory of the solar system or the arguments put forth by Creationists and anti vaccine advocates.  They are guided by ideological notions that hang by a thin thread.  Something near and dear to the hearts of the proponents of exclusive environmental determinism is threatened by evidence.  The only recourse is denial.  Its an old and tired song and dance.  Genes matter – but not exclusively.  Environment matters – but not exclusively.  Get used to it.

 

References:

 

Carmichael, M. (2010). DNA, Denial, and the Rise of “Environmental Determinism”. Wild Type. http://marycarmichael.wordpress.com/2010/12/22/dna-denial-and-the-rise-of-environmental-determinism/#comments

 

Katz, D. (2010).  Is There a Genie in the Genome? The Huffington Post. http://www.huffingtonpost.com/david-katz-md/is-there-a-genie-in-the-g_b_792844.html

 

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