Genes: still a pretty big deal

By Razib Khan | April 11, 2012 1:24 am

Many people say that having children gives you a much better sense of the power of genes in shaping behavior. At least in the abstract sense that is not true in my case. I accept the “conventional wisdom” from behavior genetics that “shared environment” (colloquially, parental input) is relatively marginal in effecting much long term change within reason (i.e., if you don’t beat your kid over the head with a baseball bat and such you don’t have much influence).

To review, on many bio-behavioral traits the different choices parents make seem to account for on the order of ~10 percent of the differences you see in the world out there amongst their (biological) offspring. Of the remainder of the variation about half of it is attributable to variation in genes, and the other half to unaccounted for non-shared environment. In The Nurture Assumption Judith Rich Harris proposes that that last effect can be reduced down to social environment or peer groups. Her line of argument is such that parents are important because of the genes they contribute, and, the environmental milieus which they select for their offspring.

On one level I find this banal to review. If it is not the orthodoxy, this position seems relatively uncontroversial, and the results fall out of the data with minimal manipulation. But as a society such facts have simply not been internalized. In the great framing of “nature vs. nurture,” appealing in its stylistic dichotomy, but not even wrong in its substance, the past few centuries have seen multiple swings between each stylized extreme. That has been a matter of ideology, not science. The popularity of public intellectuals such as Steven Pinker by the turn of the 20th century indicates to me that the high tide of post-World War II nurture-über alles has receded. But the media and popular culture are to some extent lagging indicators. They continue to trumpet correlations between parental choices and offspring outcomes as if there is a causal connection without pausing to consider the possibility both might be being influenced by a confound, genes.

Confusions as at the link above are probably why I still blog and talk about this issue incessantly. It matters in our lives, and the current state of public and personal choice simply does not take into account the real structural conditions as they manifest in the world around us. Even among many people with a biological science background who in the abstract understand genes in all their conceptual and biophysical glory there is often a concrete mystification as to the power of genes to shape behavior across the generations. This is why I get so excited when public intellectuals with some influence and following, such as Jonah Lehrer, seem to take for granted basic, but often counter-intuitive inferences from behavior genetics. For example, if you generate a perfectly egalitarian society in terms of environmental inputs, the remaining variation will be driven by genes, rendering genetic variation paramount in explaining the patterns you see around us. I’m willing to bet money that Lehrer disagrees with me on broader political philosophies, as well as detailed policies (I’m one of the few science bloggers who is a self-identified conservative). But ultimately agreeing on facts is far more important for me than the policies which we may derive from those facts (that in itself is a normative position of course!).

Which brings me back to how genetics relates to family. I have two younger brothers. One of them is rather close to my age. This is the brother with whom I grew up. We had very much the same shared environment. The other brother though is quite a bit younger. I was off at university before he was old enough for preschool. Though nominally we shared the same environment, my parents, the reality is that my parents moved, they aged many years, and their values shifted. As brothers we all do resemble each other physically, and to some extent cognitively (I am by far the least mathematical unfortunately). But, it is my youngest brother to whom I exhibit the closest physical match. And perhaps more importantly, in terms of personality, and political and religious beliefs, it is also he who resembles me more. But that’s not the strangest aspect of our resemblance. When I first did I had a confused thought that I was impersonating my youngest brother, because our mannerisms, way of speaking, etc., were just so surprisingly similar. Though I’d been told this before, I hadn’t understood the peculiarity of it. The upshot of all of this is to explain that shared and non-shared environment do little to explain why two brothers who didn’t grow up together both seem to be inexplicably attracted to paleolibertarianism and move their heads in the same manner when speaking. Especially when there’ s a third brother who seems to be a shared and non-shared environment “control” with one of the brothers, and does not exhibit those behavioral traits.

Finally, in terms of behavioral ticks I have a tendency to pick at my fingers in a very specific way. This a bad habit I’ve struggled with over my whole life. My mother has the same problem. And her mother had the same problem. The behavior isn’t exotic or mysterious. Like many people we pick at our fingers when we are anxious. So I’ll leave you with this: a few days ago my daughter apparently exhibited the exact same tick which I have, which my mother has, and which my late maternal grandmother had. I’m 99.99% sure that this 2 month old baby did not observe me picking at my fingers; when I’m with her (which is unfortunately infrequently because of my schedule) all my worries melt away. Obviously there’s no “picking at your fingers” gene. But the phenomenon just goes to show how deep rooted some behaviors can be.

* Before comments clarify, I am aware that this unaccounted for fraction may itself be genetic in the form of epistasis, or perhaps biological due to simple developmental stochasticity.

CATEGORIZED UNDER: Behavior Genetics

Comments (45)

  1. In all fairness, I decided to look up the paper after reading in the comments that the authors apparently did control for IQ/intelligence. However, after reading the paper, it seems that this is not the case, or rather, they used improper controls. First, some general remarks about the paper and the taking into account of IQ/intelligence/etc. Using the search, I found that:
    ” IQ ” is mentioned only once (in an appendix).
    “intelligence” only once, also in the appendix
    “cognitive ability” 0 results
    “academic ability” (apparently, their chosen term for general intelligence) mentioned a few times, but it seems that the control is rather poor (quoting):

    “7.7.4. Academic ability and father’s scholarly
    Onemight have legitimate concerns that home library
    size was at least in part a proxy for respondent’s aca-
    demic ability – on the argument that intelligent parents
    buy more books than usual and have smarter children
    than average. We measure academic ability by a stan-
    dardmultiple-itemtest adapted for survey use (reliability
    r = .53 over a 5-year period). Alternatively, books might
    be a proxy for father’s scholarly habitus, with fathers in
    occupations where books are common acquiring schol-
    arly skills and preferences that lead them both to buy
    books and to further their children’s educational careers.
    We measure habitus by the average home library size for
    people in father’s 4-digit occupation.
    Including these controls reduced the standardized
    effect of home library size (.27 in the base model) by
    about a quarter (to .20; Table A.8, column 3).
    18 Thus
    the effects we have estimated in the main analysis would
    probably remain at least three-quarters of their present
    size, were able to control academic ability. So even
    with this possible reduction, the effects remain large and

    I can’t find the name of the test used, and it has a very low reliability for g test at only ~0.5. AFAIK, most good g tests have reliabilities around ~0.9.

    Also, it wasn’t clear to me who they measured the ‘academic ability’ of. The child or the parents or one of the parents only (father?). The low reliability would fit if they tested the children as tests have lower reliability in children. They should have used the average of the parents or something to give a better control. Perhaps controlling for regression to the mean.

    Link to paper:

  2. I’d like to see a 2 month old who does not pick on their fingers.

  3. James

    ” They continue to trumpet correlations between parental choices…”

    That study referenced at that link was done over 20 years, in 27 countries and had a sample size of over 72,000 people, and departments at 4 universities were involved. How much did this thing cost to carry out?

  4. A lot, presumably. They showed that books in the home correlate with things. That’s OK. Causation-wise, perhaps some small effect from having books nearby (access to information), but this is rather irrelevant now a days because of the internet and internet copyright infringement. One can find a lot of ebooks and papers online, and obviously Wikipedia which is a great place to learn the basics about whatever.

  5. Darkseid

    Picking your fingers is a form of OCD and is called onychophagia

  6. Darkseid

    I meant to add that my dad has this (but doesn’t know it.) I believe “OCD genes” were passed from his mom to him and then to me and my sister (who has anorexia.) Both my grandma and I are compulsivly clean and minimalist and also pick our skin. It seems some mutations have been passed down that cause stress to cause these coping behaviors. Is anyone able to confirm my theory? Im guessing the chosen behavior depends on the individual’s receptors and what “satisfys” the individual’s stressed out brain. On the other hand, I do know that any repetitive behavior can relieve anxiety in animals (swaying in circus elephants, etc.)

  7. Charles Nydorf

    The correlation between political ideology and nature/nurture biases is actually rather complex. In France, no one thought it was unusual that Levi-Strauss was both a leftist and someone who came down on the genetic determinism side. Examples of leftist genetic determinists are not that rare in other places either, think of Chomsky.

  8. Dm

    I personally believe that these are polygenic traits at work (some of my peculiar habits are also shared with relatives I didn’t grow up with), but I’m willing to entertain a competing hypothesis that some of the stunning similarities owe to human children’s ability to emulate influential adults around them to be more liked / better preferred by the grownups. Perhaps especially for the smallest children to emulate the grown males in the family, the easier to quell the ever-present paternity doubts.

    Incidentally Razib, would you comment on this recent publication about, supposedly, genes (and nurture modifiers) behind psychological traits?
    “The Neurogenetics of Nice: Receptor Genes for Oxytocin and Vasopressin Interact With Threat to Predict Prosocial Behavior”

  9. miko

    Great title… I LOLd at “still.”

    To expand on #7… cognitive biases with a genetic basis are probably only predictive and comparable within a shared cultural milieu. As much as we (the ignorant, populist “we”, not the people here) in the U.S. see Left and Right as crystalline essences (selfish/sharing; pragmatic/idealistic; paranoid/oblivious), psychological traits that make one a member of the Left in one time and place can put one far away on the spectrum in another.

  10. S.J. Esposito

    I’ve noticed, in my family, that when there seems to be a good (or halfway decent) behavior shared between relatives, my family members chalk it up to being a learned behavior; and yet, when the behavior is bad (or extremely bad, e.g. criminal behavior), it suddenly becomes “in the genes”. Obviously, most of my family members are only HS graduates with a knowledge of genetics that they obtain from the 5 O’clock news, and as such, their view on the nature vs nurture topic is not worth much. However, it is interesting to me–and it says something about out society–at how my family reacts to shared deviant behavior as opposed to shared good behavior which they automatically assume they imparted on the younger individual by way of example.

  11. toto

    and move their heads in the same manner when speaking.

    Having unwittingly acquired the South Asian practice of shaking my head “diagonally” to express agreement and understanding, I demand a recount on this conclusion! 🙂

  12. HS graduates with a knowledge of genetics that they obtain from the 5 O’clock news, and as such, their view on the nature vs nurture topic is not worth much.

    ironically, it may count for more, due to lack of indoctrination into a weird form of quasi-blank slate nonsense 🙂

    only predictive and comparable within a shared cultural milieu.

    yeah, talked about this 7 years ago 🙂

  13. toto

    I understand that there’s been some mutterings about how low apparent shared environment effects could be an artifact of high epistasis.

    Heritability is evaluated by the difference in correlation between MZ and DZ twins. Then, SE effects are estimated from the correlation between DZ twins, minus this heritability.

    Obviously high epistasis will pump up this estimate of heritability (MZ twins are “more similar” than 2xDZ, due to the gene-gene interactions), and thereby automatically reduce the estimate of shared environment effects.

    If the “real” SE effects are small, you end up with negative values for SE and you can immediately spot the problem. But is the real SE value is large, the number may well just add up to give the illusion of additive genetic variance (oh look, r(MZ) ~= 2*r(DZ) !) .

    And that’s how you end up “proving” that trait X is highly heritable and completely additive, when in reality it has a SE component and high epistasis!

  14. Chris T

    I’ve glimpsed flashes of my wife’s personality in my 9 month old son.

    psychological traits that make one a member of the Left in one time and place can put one far away on the spectrum in another.

    Worse, political positions ascribed to one side or the other often flatly contradict the personality characteristics that each side is supposed to possess. (ie: Opposition to free trade is generally ascribed to the left, but their arguments usually stem from a desire to preserve the status quo – a conservative position by any definition.)

  15. #13, re: twins, that is why there will more like this:

    (intelligence at least seems to have been validated by genomics in regards to the twin studies; i suspect most cognitive phenotypes will, at least ones with non-trivial heritability)

  16. #14, my daughter has my facial expressions, but not my face 🙂

  17. pconroy

    Interesting. I used to bite my nails as a kid, but have reduced that behavior to picking my fingers instead. My brother also does this, and my eldest daughter now also. I inherit this from my mother, who has OCD, Bulimia and other Asperger like traits, together with a masculine 2D:4D ratio, and being good at Math.

    @6 Darkseid,
    Anorexia/Bulimia + OCD are usually attributed to Aspergers or ASD. See the work of Simon Baron-Cohen:

  18. rimon
  19. Eric


    Interesting article. I too notice “rooted behaviors” between my younger family members and their parents.

    I’m sorry for going off-topic, but in your ‘Genetics as the mythbuster: Indian edition’, would ‘South Asian’ in the admixture chart be considered the same as Ancestral South Indian?

  20. #19, post, not article. and no, 50/50 split, with a slight lean toward ASI.

  21. Anthony

    Speaking of confounds, how much do genes constrain the choices parents make in raising their children?

  22. Darkseid

    pconroy – thanks a lot for that article! i can’t believe i’d never heard of that correlation but now i have.

  23. pconroy

    @22 Darkseid,

    Your welcome!

  24. Eric


    Sorry, post.

    What present day population do you think is closest to the ASI?

  25. Karl Zimmerman

    As a parent and someone fairly determinist, there are some aspects of determinism that I really think would help liberalism if it embraced.

    As an example, consider schools, where parents are supposed to be super-concerned about getting their child into a “good” one. The problem being good is generally described by average test scores. Given the largest test score gap is between Blacks (and Latinos) and Whites (and Asians), along with to a lesser extent class, this means that parents, even supposedly “liberal” ones, often select for a school district with virtually no Black/Latino enrollment, even if they are not personally racially biased.

    Personally, as someone with above average, but not genius, intelligence, I’m confident my daughter will do fine anywhere that’s not a school so terrible she’ll have safety issues. My mother was born in a very poor family, went to a crappy school, and was her valedictorian, and had a successful professional life (even if not what she wanted to begin with). On the other hand, I went to a supposedly great school district (with only a handful of non whites, most of them Asian), yet I found I learned relatively little, because I was always reading more things, particularly about science and history, outside of school.

    I’ve seen enough of my daughter these 2.6 years to tell she’s smart. Thus I have no problem enrolling her in a racially-mixed city school, rather than doing what I’m “supposed to do” – and send her to a lily-white suburban district, or enroll her in private school. All things considered, I’d rather enjoy fixing up my Victorian house I bought for $50,000, be able to walk to things, and have my child have black friends, rather than suffer in an expensive suburb I would hate for the supposed sake of my child.

  26. #24, andaman islanders are the best proxy. low caste/tribal south indians have highest fraction. please see reich et al.

    As an example, consider schools, where parents are supposed to be super-concerned about getting their child into a “good” one

    the main issue you select for is peer group (good students make good schools; not teachers or $). if you don’t think that your child is impressionable than i think that opens up many possibilities. but as you say, a better grasp of reality produces better ‘cost vs. benefit’ calculations.

  27. Karl Zimmerman


    Both my wife and I were strange children, so I don’t see her desiring to conform by being stupid a major concern.

    We do plan on enrolling in the local magnet system (which is essentially a 50/50 split between white and black). It doesn’t get much credit in the suburbs, but Pittsburgh breaks down the test scores of white and black students, and the white students in the magnet system score as well as the average student in the most expensive school districts in the suburbs. I assume most of the difference is because the parents who care enough to apply tend to be above-average in intelligence, and thus the peer group is one for which academic achievement is important.

  28. Eric

    @Razib… Sorry to keep bugging you regarding this subject. Someone I know just shared with me this study:

    “The results suggest that the Austro-Asiatic Khasi tribes of Northeast India represent a genetic continuity between the populations of South and Southeast Asia, thereby advocating that northeast India could have been a major corridor for the movement of populations from India to East/Southeast Asia.”

    Which sparked my interest in many of the South Asian posts you’ve done (I’m Southeast Asian). So does this mean Southeast Asians are a continuum between South Asians and East Asians?

  29. DK

    that is not true in my case

    You need to wait some 20 years. It becomes much more obvious then. Particularly with N > 1.

  30. So does this mean Southeast Asians are a continuum between South Asians and East Asians?

    the short answer is that that paper is out of date. south asians are a recent hybrid between an old population (ASI) and an intrusive population from west eurasia (ANI). additionally, the austro-asiatic tribes of northeast india themselves are recent intrusive elements from southeast asia:

    (of course, in relation to the few remaining ‘negritos’ of the malay peninsula most southeast asians themselves are relatively recent intruders from what is now southern china)

  31. Kiwiguy

    I’m hopeful my daughter will grow to share my taste in 80’s pop music 🙂

  32. Darkseid

    Karl – i got sent to a “diverse” school and strongly resented it. it can easily be the difference between doing something great with your life and deciding to just try to survive. Just sayin’ that lots of hippie type parents think it’s no prob. to send their kids to a school like that because that have never had to do it themselves. it’s not worth it.

  33. Karl Zimmerman

    Darkseid –

    There’s a difference between going to a school which has some black kids, and a school which is seriously unsafe. My city has some of both, but actually some of the outlying first-ring suburban districts are more notorious for awful student conduct (like students beating up teachers) in this area.

  34. Darkseid

    I understand but I’m just saying, for your daughter’s sake, that you sound exactly like a lot of the parents were I live who decided to send their kids to my school. You can’t really know unless you go through it yourself. It’s not fun at all…

  35. Amanda S

    As someone who only met my biological kin as an adult, I can confirm that one of the most striking aspects was to find that we shared some of our mannerisms and characteristics. I was expecting to find that physical features would be shared but not this other dimension. This was of course tempered by the fact of having being raised in different countries. Other people who have a similar experience to me often comment on the same finding.

  36. Sometimes when I’m nervous and in a bad mood I clench my fists, with the thumb tucked into the other fingers, like a baby. Mostly, when getting aware of it, I also realise that I’m clamping my lips together in a particular manner. It’s then that I stop doing both immediately, because I remember having seen both with my father, being nervous, in a bad mood, and looking goofy(!)–not so enticing a remembrance. It’s in these moments that I feel, instinctively, with absolute confidence that ‘pater semper incertus est’ doesn’t apply with me (Besides, my mother told me repeatedly, sheesh!). Else, I’m also meticulous and stubborn, to put it politely (and so is my sister). Only politically we’re diverging to opposite extremes, as my liberalism got mugged when aged about 40, likely triggered by changes in my environment.

  37. Eric


    Thanks. As always, very helpful and informative.

  38. pconroy

    BTW, I have almost perfect recall on facial recognition, but have a very hard time remembering peoples names, especially first or given name. To cope, I usually give people nicknames, which are easier to remember. As a kid I would give everyone nicknames, and most farm animals too.

    Supposedly my maternal grandfather gave everyone he met a nickname, and from then on only referred to them by his given nickname.

    My son (3.5 yo) has recently started to express the same unusual trait, he will only refer to his light green duvet/comforter as “the pickle”, and has about 10 other nicknames for other items and people in his environment.

    Has anyone else any experience with this??

  39. AndrewV


    Any lingering doubts I may have had about people who subscribed to the “Blank State” were completely dispelled by the arrival of my second child.

    My conclusion was that the advocates of such, either never had children of their own, or if they did, were either not particularly involved in raising them, or some combination of being a wilfully dishonest ideologue, and which may or may not have included, neither being particularly observant nor intelligent themselves.

  40. Jings, Razib, support the head!

  41. chris w

    #7, not to make any assumptions about your own position, but “genetic determinist” seems like a bit of a misnomer. blank slate’ists frequently use the phrase “biological determinist” as a slur against the hereditarian position (which isn’t to say that you were using it this way), but it’s an inaccurate one, given that the latter attribute behavior to an interaction between genes and environment, whereas the former argue that ONLY environment matters (although they make some slight concessions, especially when politically convenient — e.g., in relation to homosexuality or transexuality). the nurture position can be more accurately described as “environmental determinism” or “cultural determinism” than the nature position can be described as “biological determinism”, as the latter is far more tolerant of cultural explanations than the former is of biological explanations. this might be a nitpick about semantics, but its dishonest use as a slur has been a source of annoyance to me — again, not to say that your use of it should be characterized as such.

  42. chris w

    I’m adopted, and I’m not similar to my adoptive parents at all, and don’t find it easy to connect with them, even though I care about them and still make regular visits. While I’m certainly happy that somebody decided to adopt me, I often caution do-gooder types who say that they would prefer to adopt from a developing country than have biological children, telling them that their adopted children might not end up relating to them very well. (With my own adoptive parents, they were not capable of producing their own child, so the situation is different.) Most of them have a nurturist assumption about personality and behavior, without having researched the issue, so I agree with Razib that research from the likes of Pinker, twin studies, etc., have yet to “trickle down”.

  43. Nihaya Khateb

    I reached the same conclusion before two years at the university forum, but all the lucturers say I talk nonsense. The same like Razib I make observations on my family ( siblings, children’ and others) but I came to another important new idea I would talk about in the evolution conference in Canada.

  44. Have more than one child and find yourself amazed at the differences.

  45. Karl Zimmerman

    As a follow-up to my point, some people might be interested at this post I made at Pittsburgh City Data, where I look in detail at how not looking at the effects of race on test scores leads parents to make the wrong impressions about city schools.

    I soft-pedaled my views on heredity a bit in order to get people to consider my broader point that there is nothing per-se wrong with the quality of city teaching. I’m not a believer in “human biodiversity” like many on here, but I am open to it playing a role once the other options have been excluded (which I think we’ll know, one way or another, within the next two decades.)


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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


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