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Nature vs. Nurture

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Many of the people I socialize with in “real life” have a biological sciences background. That being said, a relatively deep understanding of ncRNA does not give you any better sense of behavior genetics than the person off the street. And of course when you have a small child conversation often goes in the direction of how you want to raise the child so as to maximize their outcomes. Setting aside the particular normative valence of those outcomes, I am always struck by the power people think parents have over their child’s life path. This is not to say parents don’t have power. There are many young people who have college degrees because of parental expectations. Or, perhaps more precisely the social expectations which the parents set in motion by selecting the milieu of one’s children. Yet so many times I’ve been in a conversation where the phrase “I lean toward nurture” has come up. These are not dogmatic “blank slate” individuals. Rather, they are simply falling back upon the null or default of our age.

But for me here is the irony: I think it is arguably the case today we live in a world where nurture matters far less in variation in outcome of exactly the people who ‘lean toward nurture.’ Let me repeat: when you remove environmental variation by providing a modicum of comfort , you are left with genetic variation! There were times in the past when ‘nurture,’ in other words the hand that environment dealt, was much more influential. And yet during those periods it was nature which was ascendant.

In 2004 the General Social Survey asked a question where respondents were asked to decide between “genes play major role in determining personality” and “experience determines personality.” For various reasons I do not think that the question was good, but, the responses are illustrative of the unanimity we’ve achieved in American society on some questions.

 

Demographic Genes play major role Experience plays major role
Male 22 78
Female 28 72
Liberal 24 76
Moderate 25 75
Conservative 27 73
White 25 75
Black 28 72
Less than HS 28 72
High School 26 74
Junior College 25 75
Bachelor 22 78
Graduate 25 75
WORDSUM 0-4 28 72
WORDSUM 5-8 25 75
WORDSUM 9-10 25 75
Age 18-35 19 81
Age 36-65 27 73
Age 66- 37 63
God created man 30 70
Man evolved with divine guidance 23 77
Man evolved 24 76
Bible is Word of God 28 72
Bible is Inspired Word of God 27 73
Bible is Book of Fables 21 79
Protestant 27 73
Catholic 25 75
No religion 25 75
No children 20 80
1 child 25 75
2 children 29 71
3 children 25 75
4 or more children 32 68
(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Data Analysis, Nature vs. Nurture 
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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 bloggingheads.tv 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.

(Republished from Discover/GNXP by permission of author or representative)
 
• Category: Science • Tags: Behavior Genetics, Nature vs. Nurture 
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Epigenetics is making it “big time,” Slate has a review up of the new book Epigenetics: The Ultimate Mystery of Inheritance. In case you don’t know epigenetics in terms of “what it means/why it matters” holds out the promise to break out of the genes → trait conveyor belt. Instead positing genes → trait → experience → genes, and so forth. Or perhaps more accurately genes → trait × experience → genes. Epigenetics has obviously long been overlooked as a biological phenomenon. But, I think the same could be said for the ubiquity of asexual reproduction and unicellularity! Life science exhibits anthropocentrism. That’s why there’s human genetics, and biological anthropology. My own concern is that epigenetics will give some a license to posit that the old models have been overthrown, when in fact in many cases they have been modified on the margin. Especially at the level of organisms which we’re concerned about; human-scaled eukaryotes. Humans most of all.

The last paragraph in the review highlights the hope, promise, and perils of epigenetics in regards to social relevance:

It’s almost enough to make one nostalgic for the simplicity of old-style genetic determinism, which at least offered the sense that the genetic hand you were dealt at birth was the same one you would play your whole life—except that epigeneticists hold out the promise that the blessings of a single life, too, can be passed on. Disease researchers, Francis reports, have hopes that the effects of abnormal epigenesis may be reversed. For example, it’s possible that the damage caused by many cancers is epigenetic. If those epigenetic attachments can be altered, then it’s possible the cancer can be stopped. Still, even if we are discovering that an extraordinary range of conditions may be epigenetic, not all of them are. There are still specific diseases that follow a deterministic path. If you are unlucky enough to draw the Huntington’s mutation in the genetic shuffle, you will develop the disease. Francis rightly emphasizes the wonder of epigenetics and the molecular rigor it brings to the idea that life is a creative process not preordained by our genome any more than it is preordained by God. Yet even as epigenetic research invites dreams of mastery—self-creation through environmental manipulation—it also underscores our malleability. There is no easy metaphor for this combination. But if we must have one, we should at least start with the cell, not the gene. The genome is no blueprint, but maybe the cell is a construction site, dynamic, changeable, and complicated. Genes are building materials that are shaped by the cell, and they in turn create materials used in the cell. Because the action at the site is ongoing, a small aberration can have a small effect, or it can cascade through the system, which may get stuck. Recall that your body is a moving collection of these building sites, piled in a relatively orderly way on top of another. Malleability? It’s an ongoing dance with chaos, but, incredibly, it works.

If people have a hard enough time with the concept of heritability, I have no idea how they’ll deal with heritability of epigenetic modifications! In science itself epigenetics has really come to the fore over the last 10 years. Here’s a plot which shows the change over time in the scientific literature:

And here’s the Google Trends results:

Either the media only discovered epigenetics in 2008, or Google’s index wasn’t very good. I suspect the former, as I started being asked about the term by intellectual non-science types circa 2008. For Google Correlate “epigenetic” and “subjective” have a correlation of 0.91, and “epigenetics” and “we create” have a correlation of 0.89. These are a little disturbing, and I hope epigenetics doesn’t go the way of quantum theory and general relativity and become abused in other disciplines. For example, “epigenetics means that genetic inheritance is a subjective fiction!”

(Republished from Discover/GNXP by permission of author or representative)
 
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Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at http://www.razib.com"