Distributing the origins of human will

By Razib Khan | October 7, 2012 9:26 pm

In The New York Times David P. Barash writes about how parasites might influence our behavior. This should not be too shocking an idea to readers of this weblog, I’ve blogged about Toxoplasma gondii before, on which there has been a raft of publications over the past 10 years or so. My main issue is that like much of behavior genomics I wonder about the possibility of any terminus and conclusion to this line of inquiry (as opposed to being fodder for high publicity publications indefinitely). For any given personality trait we know that a small proportion (on the order of 10 percent) of the predicted variation within the population is due to variation in family environment (i.e., the impact of parent-specific choices). Of the remaining fraction it is about evenly split between genetic effects (i.e., the genes you inherit from your parents, and the consequent dispositions) and “other/non-shared environmental effects.”

This last is really just a residual; we don’t know what’s going on within the model. In The Nurture Assumption Judith Rich Harris posited that much of the remaining environmental component was peer effects. But there are other possibilities. Perhaps strangely, this environmental component could in part be types of genetic variation not captured by the genetic effect proper (e.g., epistasis). Or, it could be developmental noise, which might be biologically fixed rather early on in life. More recently people have wondered if it could be epigenetic variation. And of course, it could be parasites.

If I had to bet money I suspect that most of the heritable genetic variation for most behavioral traits will be widely distributed across the genome. In other words, many genes of small cumulative effect. This means that in many cases we won’t have a ‘silver bullet’ ‘X [trait] gene.’ But why should we limit this to genetic effects? Why would we expect a few classes of parasites to be responsible for most of the behavioral variation due to parasites? Or one particular environmental input as the root cause of cross-cultural variation (e.g., some have adduced that differences between Eastern and Western cultures might be due to the alphabetic literacy of the latter)? To some extent this is building a case for pessimism about the power of reductionism in smoking out causal chains. On the one hand we may be able to robustly and confidently partition components of variation. And yet we may have difficultly in ascertaining the exact details of the haze of causal factors which sum up together to produce the phenotypes we see around us. I have no problem with this, but it seems that for broad acceptance of any given effect (genetic or environmental) it is often important to point to a specific gene or environmental causal agent.

CATEGORIZED UNDER: Behavior Genetics
MORE ABOUT: Behavior Genetics
  • Prof.Pedant

    With complicated things like behavior understanding the causes seems to generally be a matter of haze. My impression is that our understanding of human behavior and genetics in general is getting to the point where we are beginning to glimpse that no matter how much we can pin down – and we can pin down a lot – there will always be a haze of uncertainty about which gene or which experience had what sort of contribution to either specific behavior or general patterns of behavior. That being said, I’m comfortable with ambiguity and uncertainty arising from a deeper understanding – bring on the facts!

  • CouriousScientist

    Razib writes:
    “For any given personality trait we know that a small proportion (on the order of 10 percent) of the predicted variation within the population is due to variation in family environment (i.e., the impact of parent-specific choices). Of the remaining fraction it is about evenly split between genetic effects (i.e., the genes you inherit from your parents, and the consequent dispositions) and “other/non-shared environmental effects.””

    I’m surprised by the confidence with which this is expressed. It would seem to me that the state of the literature is much muddier that that. Could you point us to a scientific article supporting this statement?

    Also, I am unclear what the population is Razib is referring to. Is it all human beings, or is it north american college students, or is it adopted twins? Relatedly, is this a statement about inter-individual differences only, or is it also a statement about group differences?
    I think this makes a huge differences, but unfortunately it is not clear to me from the way it is written. (I would think the gene would play a much larger role in the explanation of inter-individual-differences (jack’s and john’s intelligence) as compared to in the explanation of group differences (average IQ’s in the upper west side and in some rural village in india/china/brasil/nigeria/) )

  • John Emerson

    For any given personality trait we know that a small proportion (on the order of 10 percent) of the predicted variation within the population is due to variation in family environment (i.e., the impact of parent-specific choices). Of the remaining fraction it is about evenly split between genetic effects (i.e., the genes you inherit from your parents, and the consequent dispositions) and “other/non-shared environmental effects.”

    Isn’t the distinction between “family” v. “non-shared” environmental effects particularly sharp in a liberal-pluralist-free-speech society? Not a law of nature, but a function of the fact that parents have little control over kids’ environments, with the non-shared environment extraordinarily diverse, and almost never working to reinforce parental values and customs? You’re always reading stories about kids in strict religious environments liberating themselves by listening to the radio in secret, listening to their friends’ music away from home, etc.

    Contrast, for example, a Hasidic Jew in NYC or an Amish kid or a Parsi in India, or any other case when the parent is able to raise their kids in a relatively homogenous culture. The nuclear family environment v. non-family environment divide would still be there, but it would be less evident because much of the non-shared environment would be similar to the family environment. And there would still be Amish kids far different than their parents, but they’d still be within the Amish frame and the differences would be more clear to Amish than to outsiders.

    This is a lot of what people mean by “the decline of the family”. Parents find that the 45% non-shared environment tends to overwhelm the 10% shared-environment.

    This is true for parents of any description.

  • http://jaymans.wordpress.com/ JayMan

    Here’s a collection of related posts, from myself and others:

    Depths of Madness | West Hunter – Greg Cochran on the possibility that homosexuality is caused by a pathogen.

    About Developmental Noise | JayMan’s Blog – Myself on methylation and developmental noise

    A comment by me on Half Sigma about peer influence and its limits

    Discussion between HBD Chick and I about free will (and its non-existence)

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    It would seem to me that the state of the literature is much muddier that that.

    if you have a sense of the scientific literature, why are you asking me the following: Also, I am unclear what the population is Razib is referring to.

    again, if you have a sense of the literature why the are you asking me this? the literature in this area is rather specific, as is the way these variance proportions are computed. you should know. i’m not talking about he behavior genetic research from planet zorkon.

    if you don’t know, don’t preface your ignorance with your own personal assessment of the state of the ‘literature.’ if you do know, then come out an baldy state your scientific opinion instead of tip-toeing.

    here’s a link. see start of second paragraph:

    http://tinyurl.com/9oeoe3t

    any weasel follow-up comments similar to your first one will result in removal of the comment and banning. if you disagree with the behavior genetic literature (and some people do), just state why.

    Not a law of nature

    these proportions are computed in particular contexts. so yes, one can imagine them varying. ergo, the famous turkheimer study from the early 2000s that heritability of IQ is higher in higher SES than lower SES. probably more robustly, you see the same tendency in height.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    #2, btw, i looked you up. does neurocognition intersect with behavior genetics much?

  • Hemo_jr

    Assuming that any behavioral influence is parasitic is prejudicial. A behavioral influence may actually be beneficial/mutualistic.

    My guess is that the biggest influence on our behavior is the result of an individual’s gut biome. This influence would be either indirect in affecting what an individual eats and how his/her system handles it. Or it may influence the way one’s gut reacts to fear, for example. If the gut biome influences, either by calming or exaggerating the reaction of the gut when an individual is faced by a threat, that would be significant.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    #7 the fact that i have little ecological background shows!

    re: gut biome. we have a massive natural experiment: caesarian vs. non-caesarian births are different in this dimension from what i recall.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    #3, let me make what is being inferred here explicit by an example of how it may be confounded. imagine a population of equal parts:

    -ethnic finns raised in finland
    -ethnic finns raised in spain
    -ethnic spaniards raised in finland
    -ethnic spaniards raised in spain

    i predict if you pooled these together and estimated heritable proportions of personality traits they’d be much lower than within a given nation. the common sense reason is that all conditions aren’t equalized, and inter-cultural norms and expectations are very different. i think it is likely that for biological [genetic, microbiome, epigenetic] reasons ethnic finns may exhibit more introversion than ethnic spaniards. but, this expresses itself in an environmental context, and ethnic finns raised in spain may be more outgoing than ethnic spaniards raised in finland, because of the cultural milieu in which they developed.

    this brings up whether these estimations are useful or not. yes! most people don’t migrate across nations, and compare their own practices in child-rearing, etc., to their “ingroup.” a great deal of the “bringing up baby” is actually a function of group values and peer pressure. this is an insight that is valuable. just as is the insight that not all conditions are always held equal (the difference between spain and finland may even be biological in terms of microbiome conditioned on climate!).

  • John Emerson

    I have met half of a cross-cultural twin study — after a divorce one twin went to India with the father and the other stayed in the US with the mother. As the American twin told it, her sister was living the traditional elite life of whichever group they belonged to, and the woman I know was living the upward-mobile lower-middle-class life.

    There’s also a demographic called Holt babies of Korean kids adopted By Americans. Several hundred I think. However, finding siblings in Korea is apparently difficult to impossible.

    Educated, ambitious prosperous parents I know are pretty vigilant about scheduling their kids’ time starting very young, choosing their friends, etc., the way other parents (except for the very religious) are not. And the religious parents have terrible problems. which is why they hate the public schools. It takes a fair amount of resources to channelize a kids life effectively.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    #10, fascinating. with mother information technology i’ve hopeful we can collect more data sets of weird cases like twins raised in separate cultures. also, re: ‘ambitious parents’ etc., the main insight from behavior genetics is that the people who have gone through the meritocratic filter in the modern west and inculcate these values in their children are already the types who will have children well disposed to take these lessons and extend them throughout their lifetime, and repeat the same pattern with their own children. IOW, there’s a genetic conditionality on the learned behavior. depending on the trait adopted children of upper middle class parents tend to be able to follow the script as long as they’re under their parents’ supervision, but start to deviate from the expected path once they leave the home (presumably seeking out their own environments).

  • John Emerson

    Razib, you’re in a perfect position to test the theory. Two very bright parents and no parental guidance…. it might work.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    #12, we will be biased toward the ‘free range’ end, at least according to 2012 norms of middle class college educated people. who knows what the fat in the 2020s will be when she will hit her teens?

    fwiw, my youngest brother is 15 years younger than i am, and is the most similar to me in terms of personality (as opposed to my brother with whom i grew up). we were raised totally differently (i was left alone and minimally supervised, he was overprotected to an extreme degree).

  • John Emerson

    Vladimir Nabokov was a Russian aristocrat who wrote great novels in two languages, wrote chess puzzles, coached tennis, and made actual contributions to lepidoptery (beyond the collecting and cataloging — he figured out the evolutionary and migration history of a butterfly which migrated from Asia to the Americas and back.

    In his autobiography he seems to have been left more or less free, but if he showed an interest in something his parents would make sure that he had the materials to proceed as far as he was able to and wanted to. He also had a lot of interaction with adults though he also did kid stuff. (He does mention one cousin who was a frat boy sort of the wilder sort who went into the military — possibly a different outcome of the same childraising method).

    The variable here isn’t attempts to mold the child, but the provision of a helpful environment. Something which might be corrupting these studies is the fact that a lot of parents work very hard on molding their kids, but because they’re fairly clueless and are working from paint-by-numbers parenting manuals it comes to nothing.

  • Sandgroper

    #10 – The Devil makes work for idle hands.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    paint-by-numbers parenting manuals it comes to nothing.

    parenting fads seem to be pretty much about fashion, signalling, etc., rather than genuine increase in utility. e.g., the whole “missing child” paranoia of the 80s has resulted in (at least this is often assumed to be part of the cause) kids being shuttled around by parents in minivans constantly. this may allay psychic stress, but it probably has almost no impact on children being kidnapped (in probably increases the number of deaths of kids in car crashes, and also the kids walking the streets of suburban communities).

    basically there are common sense things which we can agree on. e.g., don’t beat the shit out of your kids, you might damage their brains. if you want a close relationship with your child and want to beat them regularly, make sure that your children are raised in a society where parents beating children are socially sanctioned activities, so your kid won’t hold it against you when they grow up (this is a frustration of many immigrants from primitive societies; western child protective services tend to frown up severe beatings, rather than validating the parents’ lack of impulse control).

  • CouriousScientist

    In reply to Razibs commente 5 & 6:

    Yes, I am a cognitive neuroscientist, though my background is more in quantitative models of cognition. Check out my publications, if you think this is relevant: http://scholar.google.com/citations?user=0UkWz9IAAAAJ&hl=en. I don’t feel I need to be anonymous. You’ll even find a genetics paper ;-)!

    First of: Yes, my impression (from discussion with colleagues doing genetics studies, not from following the literature!) is that it easily happens that behavioral genetics studies are over-interpreted. For example, I cannot remember that in discussion of twins studies the genetic effects are put into perspective by pointing out that heritability coefficients do depend a lot on the variability of the environment (Except of course by those who do not believe in very strong effects of genes). But then, as I said, I don’t follow the literature very close, and maybe this is generally done (I’d be surprised though).

    I was in no way trying to “preface your ignorance with your own personal assessment of the state of the ‘literature” as you so elegantly phrased. So I’ll rephrase my comment/question.
    1) I do not follow the behavioral genetics literature closely
    2) Still, I think (intuitively, not based on deeper reading of the literature) that the relationship between genes, environment, and phenotype is rather complex, and that detrimental environments should have severe impacts on phenotypes such as personality traits
    3) Therefore, I am surprised that you make a statement (about heritability) that seems very strong to me
    4) Hence, I wondered (and still wonder) if you can point your readers to any literature that substantiates such a statement.

    As you see, I do not give answer to your question about literature. This is because my point was not based on my knowledge about the literature but based on general skepticism and a simple statistical insight. (Though a quick search brought up this interesting paper about heritability, group differences. Note: I only read the abstract! http://www.ncbi.nlm.nih.gov/pubmed/11381833)
    I don’t claim to be an expert in the field. Given that you write a blog about genetics and I thus think that you are more expert in this field than I am, I thought you might know of papers that support your general statement (I’m referring to the large role of genes here, not to the small role of shared familial environment), even if I think it is unlikely that there are such papers. But I think it is unlikely but certainly not impossible.

    As to your link (http://tinyurl.com/9oeoe3t): I think this is about the role of shared familial environment being overestimated by many social scientists. I have no problem with this statement and can readily accept it (i.e., off my hat I can’t think of a statistical argument that makes me doubt it).
    However, this was not that point of my comment. The point of my comment was that I believe that if one makes statements about heritability one should be very clear about (a) what population one is speaking about and (relatedly) (b) if one is talking about inter-individual differences or about groups differences. I think so because I believe most readers are naive about these points, which I think are important.

    Your citation of the Tuerkheimer study (which I even didn’t remember …) suggests that you are well aware of these points, you just didn’t mention them in your post above.

    I don’t disagree with the behavior genetics literature, but I think that it is easy to misread its result. More specifically: If a twin study finds a genetic heritability of 80% I’m fine with that, and I wouldn’t dream of dismissing such a result. What I would not be fine with is when one generalizes this result to a population that is systematically different than the study population. (e.g. because the study sample has a lower variance in environmental variables than the population one would like to make a statement about). I think this a reasonable, if uncomfortable expectation. (Note that I am as skeptic about neuroimagers who generalize from simplified tasks to cognition in the “real world”)

    About your threat to ban me/delete my comment: That seems a bit over the top to me. I don’t think that I violated any of your rules, even if I disagree that a reader always has to answer the blogger. I assume that who ever stopped a conversation (i.e. stops providing arguments) that is not resolved either ran out of arguments or wasn’t very serious in the first place.

  • https://plus.google.com/109962494182694679780/posts Razib Khan

    Check out my publications

    your email is linked to your facebook. i already perused your pubs ;-)

    twins studies the genetic effects are put into perspective by pointing out that heritability coefficients do depend a lot on the variability of the environment

    this is well known, and assumed.

    The point of my comment was that I believe that if one makes statements about heritability one should be very clear about (a) what population one is speaking about and (relatedly) (b) if one is talking about inter-individual differences or about groups differences. I think so because I believe most readers are naive about these points, which I think are important.

    most of my core readers are well aware of these issues. those who are not core readers are quite made well aware if they comment.

    Your citation of the Tuerkheimer study (which I even didn’t remember …) suggests that you are well aware of these points, you just didn’t mention them in your post above.

    the target of these posts are middle to upper middle class western people. that’s because that’s who reads this blog (according to survey).

    What I would not be fine with is when one generalizes this result to a population that is systematically different than the study population.

    i tend to be precise about these issues, in that if i don’t say something, i don’t mean it. if i larded every post with every qualification to head off every possible possibility toward confusion i would never finish a post.

    I assume that who ever stopped a conversation (i.e. stops providing arguments) that is not resolved either ran out of arguments or wasn’t very serious in the first place.

    do you have a blog? if so, what are your standards?

    i believe in your follow up to the initial comment you have validated exactly my aggressive and brutal response style. the follow up comment was elaborate, precise, and detailed. you were clear in what you intended, and where you came from. that was my intention. if you didn’t adapt forthwith, then i wouldn’t have seen the point of engagement. and indeed there are MANY people who are “in the game” to hear themselves speak. that sort i silence.

  • Justin Giancola

    16 is a great post! When do we get that like feature we’ve been clamouring about? ;)

  • Douglas Knight

    I don’t know how contagious most parasites are, but I would expect them to show up as shared environment, not residual unshared. Certainly, exposure to house cats is shared environment.

NEW ON DISCOVER
OPEN
CITIZEN SCIENCE
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

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

ADVERTISEMENT

See More

ADVERTISEMENT

RSS Razib’s Pinboard

Edifying books

Collapse bottom bar
+

Login to your Account

X
E-mail address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »