Heritable, yes, which gene…another issue

By Razib Khan | April 8, 2010 9:10 am

Dr. Daniel MacArthur points to a long article by Edmund Yong, Dangerous DNA: The truth about the ‘warrior gene’. Dr. MacArthur notes on his twitter account: “Nice piece on behavioural genetics…but should emphasize MOST behav. gene assocs are actually false.” I think he’s pointing to the winner’s curse; there are lots of people studying various topics, but only a subset of studies pass which yield appropriate effect sizes and p-values actually get published. A sequence of such may give a false sense of certitude as to the strength of the association between a locus and a trait, as negative results are not usually published. I hope David Dobbs keeps this in mind in relation to his new book on the ‘orchid hypothesis’. We have decades of research which suggest that a lot of human behavior is due to variation in genes within the population. In other words, many psychological traits and predispositions are heritable. But both the earlier linkage studies and now the associations which try and establish a particular gene as the primary causal factor are much more provisional, and like much of science wrong or ultimately of marginal long term value.

The incredible amount of press which genetics and genomics research with behavioral implications receive in the press is more about our psychology than the state of science as it is now. Similarly, consider the enormous swell of neuroimaging research within the past decade. Both genetics and neuroscience offer up the possibility of establishing a sturdier biophysical grounding for the human sciences, but we shouldn’t get ahead of ourselves. Finally, the fact that we know that psychological traits are heritable is useful in and of itself, whether we know the underlying genetic architecture of the trait or the neurobiology mediating between the genetic and behavioral level. Look to the parents, and you shall know a great deal.

CATEGORIZED UNDER: Genetics, Genomics, Science
  • Chris T

    I have a sneaking suspicion that most of the genetic association data we’re accruing will have been thrown out twenty years from now.

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  • dan

    Raz, (you don’t mind if I call you Raz, do you?;) Can you give insight as to how a trait or behavior can only be 50% heritable or 80% due to gene variance? How can a phenotype be *sometimes* genetic? What else could it be since we’re nothing but genes and bacteria? Is it due to gene *expression* variance? Is it due to junk DNA variance? I just don’t understand how a trait can be genetic half the time and the other half of the time it happens to be cause by environment yet is expressed the same way. It seems like it’d have to be purely cultural (something we wouldn’t instinctively do without prior knowledge) or purely genetic. I’m probably missing something big but that;s why I want to learn.
    Also, did you see this cool video where these little creatures can repair their own DNA using scraps from other downed organisms?
    http://www.youtube.com/watch?v=ytJ1yvFPbTE

    and here’s a funny cat. thanks for all the great work over the years.
    http://i.imgur.com/S6KOr.png

  • miko

    dan, wikipedia is a good place to start…read the entry on heritability. The key: it’s a population measure, not a measurement of what happens in one individual.

    Height in humans is always a good example–it is highly heritable for the well-fed, and involves many genes with tiny effects. Although it used to be assumed that highly heritable traits would be associated with a few loci of large effect, this seems to not be the case (though we don’t have lots of examples). On the other hand, for undernourised people, how tall you get depends more on your diet than on your genes. Height has a relatively low heritability in these cases. Same trait, same biology, different heritabilities.

    Many phenotypes of interest are the result of complex interactions between genes and environment that go both ways. The environment can influence the expression or functions of genes (or, if you prefer, genes and proteins respond to the environment). The opportunities for complexity and nonlinear interactions are enormous.

    In behavior, there is the added complexity of nervous system plasticity. In development, we over-produce neurons and synapses at a huge rate and prune them back based on utility. There is evidence that stochasticity at the level of gene regulation plays a part in generating neuronal diversity. In the view of these models, there is a mini-Darwinian process of variation and competition among neurons in every toddler’s skull. Genes certainly specify this rules of this game, but it is complex and exquisitely responsive to sensory stimulation and other environmental inputs.

    Finally, humans are super duper complicated. We have culture…our genes make this possible, because they specify the brains and hands and larynxes that make culture possible. These biological features constrain what culture can be, but only loosely (from our perspective). My view of social behavior is that there has probably been a lot more selection on the cognitive ability to mold yourself to the culture in which you find yourself–i.e. to “fit in”, survive, etc– than to specify cultural elements in any particular way.

    There are a lot of books about this.

  • dan

    miko, thanks a lot for the info. i really really enjoyed the wiki article as well. i think i made a truly key understanding when i read one of the lines in particular:

    “A more useful distinction than “nature vs. nurture” is “obligate vs. facultative”….”

    this is where i was confused. Am I correct in saying that heritability is showing the “genetic sensitivity” amongst a population for a particular phenotype? Meaning, a trait with lower heritability is a gene or set of genes/proteins that are *more* sensitive to environmental/cultural pressures? general intelligence is less influenced by environment where as neuroticism or political inclination is more influenced by environment? is this correct? and do I need to add anything?

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    Am I correct in saying that heritability is showing the “genetic sensitivity” amongst a population for a particular phenotype? Meaning, a trait with lower heritability is a gene or set of genes/proteins that are *more* sensitive to environmental/cultural pressures?

    no. traits which are VERY genetically controlled often have low heritability. this is because most of the variance is due mutations which are de novo and such. there is a distinction between *genetic* traits and *heritable* traits. additionally, many heritable traits are highly sensitive to environment. like height. it is 80-90% heritable, but highly sensitive to environment. it just so happens that in developed societies nutritional inputs are saturated, so the only variance remaining is genetic.

    the only caveat to miko’s post is that i think you can use heritability cautiously in individual cases. though since it’s a pop level statistic it should be done with a lot of care. see steve hsu:
    http://infoproc.blogspot.com/2008/10/regression-to-mean.html

  • dan

    ok, thanks a lot Razib. i think i’m slowly understanding the basics.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    dan, go to the univ. library and read the chapter which discusses heritability of traits in hartl & clark.

  • dan

    I’m a tad worried that’s a bit over my head….but I ordered this last night:
    http://www.amazon.com/Genes-Behavior-Nature-Nurture-Interplay-Explained/dp/1405110619/ref=pd_ys_iyr_img

    is that good enough? Also, I’m sifting through this talk with DS Wilson:
    http://www.youtube.com/watch?v=9Cz8ZwaJe24&feature=player_embedded#
    he seems like the king of evo-bio. any qualms with DSW?

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Gene Expression

This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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