Nature via Nurture

JDN 2457222 EDT 16:33.

One of the most common “deep questions” human beings have asked ourselves over the centuries is also one of the most misguided, the question of “nature versus nurture”: Is it genetics or environment that makes us what we are?

Humans are probably the single entity in the universe for which this question makes least sense. Artificial constructs have no prior existence, so they are “all nurture”, made what we choose to make them. Most other organisms on Earth behave accordingly to fixed instinctual programming, acting out a specific series of responses that have been honed over millions of years, doing only one thing, but doing it exceedingly well. They are in this sense “all nature”. As the saying goes, the fox knows many things, but the hedgehog knows one very big thing. Most organisms on Earth are in this sense hedgehogs, but we Homo sapiens are the ultimate foxes. (Ironically, hedgehogs are not actually “hedgehogs” in this sense: Being mammals, they have an advanced brain capable of flexibly responding to environmental circumstances. Foxes are a good deal more intelligent still, however.)

But human beings are by far the most flexible, adaptable organism on Earth. We live on literally every continent; despite being savannah apes we even live deep underwater and in outer space. Unlike most other species, we do not fit into a well-defined ecological niche; instead, we carve our own. This certainly has downsides; human beings are ourselves a mass extinction event.

Does this mean, therefore, that we are tabula rasa, blank slates upon which anything can be written?

Hardly. We’re more like word processors. Staring (as I of course presently am) at the blinking cursor of a word processor on a computer screen, seeing that wide, open space where a virtual infinity of possible texts could be written, depending entirely upon a sequence of miniscule key vibrations, you could be forgiven for thinking that you are looking at a blank slate. But in fact you are looking at the pinnacle of thousands of years of technological advancement, a machine so advanced, so precisely engineered, that its individual components are one ten-thousandth the width of a human hair (Intel just announced that we can now do even better than that). At peak performance, it is capable of over 100 billion calculations per second. Its random-access memory stores as much information as all the books on a stacks floor of the Hatcher Graduate Library, and its hard drive stores as much as all the books in the US Library of Congress. (Of course, both libraries contain digital media as well, exceeding anything my humble hard drive could hold by a factor of a thousand.)

All of this, simply to process text? Of course not; word processing is an afterthought for a processor that is specifically designed for dealing with high-resolution 3D images. (Of course, nowadays even a low-end netbook that is designed only for word processing and web browsing can typically handle a billion calculations per second.) But there the analogy with humans is quite accurate as well: Written language is about 10,000 years old, while the human visual mind is at least 100,000. We were 3D image analyzers long before we were word processors. This may be why we say “a picture is worth a thousand words”; we process each with about as much effort, even though the image necessarily contains thousands of times as many bits.

Why is the computer capable of so many different things? Why is the human mind capable of so many more? Not because they are simple and impinged upon by their environments, but because they are complex and precision-engineered to nonlinearly amplify tiny inputs into vast outputs—but only certain tiny inputs.

That is, it is because of our nature that we are capable of being nurtured. It is precisely the millions of years of genetic programming that have optimized the human brain that allow us to learn and adapt so flexibly to new environments and form a vast multitude of languages and cultures. It is precisely the genetically-programmed humanity we all share that makes our environmentally-acquired diversity possible.

In fact, causality also runs the other direction. Indeed, when I said other organisms were “all nature” that wasn’t right either; for even tightly-programmed instincts are evolved through millions of years of environmental pressure. Human beings have even been involved in cultural interactions long enough that it has begun to affect our genetic evolution; the reason I can digest lactose is that my ancestors about 10,000 years ago raised goats. We have our nature because of our ancestors’ nurture.

And then of course there’s the fact that we need a certain minimum level of environmental enrichment even to develop normally; a genetically-normal human raised into a deficient environment will suffer a kind of mental atrophy, as when children raised feral lose their ability to speak.

Thus, the question “nature or nurture?” seems a bit beside the point: We are extremely flexible and responsive to our environment, because of innate genetic hardware and software, which requires a certain environment to express itself, and which arose because of thousands of years of culture and millions of years of the struggle for survival—we are nurture because nature because nurture.

But perhaps we didn’t actually mean to ask about human traits in general; perhaps we meant to ask about some specific trait, like spatial intelligence, or eye color, or gender identity. This at least can be structured as a coherent question: How heritable is the trait? What proportion of the variance in this population is caused by genetic variation? Heritability analysis is a well-established methodology in behavioral genetics.
Yet, that isn’t the same question at all. For while height is extremely heritable within a given population (usually about 80%), human height worldwide has been increasing dramatically over time due to environmental influences and can actually be used as a measure of a nation’s economic development. (Look at what happened to the height of men in Japan.) How heritable is height? You have to be very careful what you mean.

Meanwhile, the heritability of neurofibromatosis is actually quite low—as many people acquire the disease by new mutations as inherit it from their parents—but we know for a fact it is a genetic disorder, because we can point to the specific genes that mutate to cause the disease.

Heritability also depends on the population under consideration; speaking English is more heritable within the United States than it is across the world as a whole, because there are a larger proportion of non-native English speakers in other countries. In general, a more diverse environment will lead to lower heritability, because there are simply more environmental influences that could affect the trait.

As children get older, their behavior gets more heritablea result which probably seems completely baffling, until you understand what heritability really means. Your genes become a more important factor in your behavior as you grow up, because you become separated from the environment of your birth and immersed into the general environment of your whole society. Lower environmental diversity means higher heritability, by definition. There’s also an effect of choosing your own environment; people who are intelligent and conscientious are likely to choose to go to college, where they will be further trained in knowledge and self-control. This latter effect is called niche-picking.

This is why saying something like “intelligence is 80% genetic” is basically meaningless, and “intelligence is 80% heritable” isn’t much better until you specify the reference population. The heritability of intelligence depends very much on what you mean by “intelligence” and what population you’re looking at for heritability. But even if you do find a high heritability (as we do for, say, Spearman’s g within the United States), this doesn’t mean that intelligence is fixed at birth; it simply means that parents with high intelligence are likely to have children with high intelligence. In evolutionary terms that’s all that matters—natural selection doesn’t care where you got your traits, only that you have them and pass them to your offspring—but many people do care, and IQ being heritable because rich, educated parents raise rich, educated children is very different from IQ being heritable because innately intelligent parents give birth to innately intelligent children. If genetic variation is systematically related to environmental variation, you can measure a high heritability even though the genes are not directly causing the outcome.

We do use twin studies to try to sort this out, but because identical twins raised apart are exceedingly rare, two very serious problems emerge: One, there usually isn’t a large enough sample size to say anything useful; and more importantly, this is actually an inaccurate measure in terms of natural selection. The evolutionary pressure is based on the correlation with the genes—it actually doesn’t matter whether the genes are directly causal. All that matters is that organisms with allele X survive and organisms with allele Y do not. Usually that’s because allele X does something useful, but even if it’s simply because people with allele X happen to mostly come from a culture that makes better guns, that will work just as well.

We can see this quite directly: White skin spread across the world not because it was useful (it’s actually terrible in any latitude other than subarctic), but because the cultures that conquered the world happened to be comprised mostly of people with White skin. In the 15th century you’d find a very high heritability of “using gunpowder weapons”, and there was definitely a selection pressure in favor of that trait—but it obviously doesn’t take special genes to use a gun.

The kind of heritability you get from twin studies is answering a totally different, nonsensical question, something like: “If we reassigned all offspring to parents randomly, how much of the variation in this trait in the new population would be correlated with genetic variation?” And honestly, I think the only reason people think that this is the question to ask is precisely because even biologists don’t fully grasp the way that nature and nurture are fundamentally entwined. They are trying to answer the intuitive question, “How much of this trait is genetic?” rather than the biologically meaningful “How strongly could a selection pressure for this trait evolve this gene?”

And if right now you’re thinking, “I don’t care how strongly a selection pressure for the trait could evolve some particular gene”, that’s fine; there are plenty of meaningful scientific questions that I don’t find particularly interesting and are probably not particularly important. (I hesitate to provide a rigid ranking, but I think it’s safe to say that “How does consciousness arise?” is a more important question than “Why are male platypuses venomous?” and “How can poverty be eradicated?” is a more important question than “How did the aircraft manufacturing duopoly emerge?”) But that’s really the most meaningful question we can construct from the ill-formed question “How much of this trait is genetic?” The next step is to think about why you thought that you were asking something important.

What did you really mean to ask?

For a bald question like, “Is being gay genetic?” there is no meaningful answer. We could try to reformulate it as a meaningful biological question, like “What is the heritability of homosexual behavior among males in the United States?” or “Can we find genetic markers strongly linked to self-identification as ‘gay’?” but I don’t think those are the questions we really meant to ask. I think actually the question we meant to ask was more fundamental than that: Is it legitimate to discriminate against gay people? And here the answer is unequivocal: No, it isn’t. It is a grave mistake to think that this moral question has anything to do with genetics; discrimination is wrong even against traits that are totally environmental (like religion, for example), and there are morally legitimate actions to take based entirely on a person’s genes (the obvious examples all coming from medicine—you don’t treat someone for cystic fibrosis if they don’t actually have it).

Similarly, when we ask the question “Is intelligence genetic?” I don’t think most people are actually interested in the heritability of spatial working memory among young American males. I think the real question they want to ask is about equality of opportunity, and what it would look like if we had it. If success were entirely determined by intelligence and intelligence were entirely determined by genetics, then even a society with equality of opportunity would show significant inequality inherited across generations. Thus, inherited inequality is not necessarily evidence against equality of opportunity. But this is in fact a deeply disingenuous argument, used by people like Charles Murray to excuse systemic racism, sexism, and concentration of wealth.

We didn’t have to say that inherited inequality is necessarily or undeniably evidence against equality of opportunity—merely that it is, in fact, evidence of inequality of opportunity. Moreover, it is far from the only evidence against equality of opportunity; we also can observe the fact that college-educated Black people are no more likely to be employed than White people who didn’t even finish high school, for example, or the fact that otherwise identical resumes with predominantly Black names (like “Jamal”) are less likely to receive callbacks compared to predominantly White names (like “Greg”). We can observe that the same is true for resumes with obviously female names (like “Sarah”) versus obviously male names (like “David”), even when the hiring is done by social scientists. We can directly observe that one-third of the 400 richest Americans inherited their wealth (and if you look closer into the other two-thirds, all of them had some very unusual opportunities, usually due to their family connections—“self-made” is invariably a great exaggeration). The evidence for inequality of opportunity in our society is legion, regardless of how genetics and intelligence are related. In fact, I think that the high observed heritability of intelligence is largely due to the fact that educational opportunities are distributed in a genetically-biased fashion, but I could be wrong about that; maybe there really is a large genetic influence on human intelligence. Even so, that does not justify widespread and directly-measured discrimination. It does not justify a handful of billionaires luxuriating in almost unimaginable wealth as millions of people languish in poverty. Intelligence can be as heritable as you like and it is still wrong for Donald Trump to have billions of dollars while millions of children starve.

This is what I think we need to do when people try to bring up a “nature versus nurture” question. We can certainly talk about the real complexity of the relationship between genetics and environment, which I think are best summarized as “nature via nurture”; but in fact usually we should think about why we are asking that question, and try to find the real question we actually meant to ask.

11 thoughts on “Nature via Nurture

  1. Have you considered that sports, with its very quantifiable data, may provide examples where contrasts between nature can be made? Track would be a good starting point.


    • Well, we can quantify the results well enough, but can we quantify the causes? We can tell that a given athlete is better than another, but how do we tell whether it is because of his genes or his experiences?

      Lance Armstrong, for example, has a number of unusual biological traits that make him such an exceptional athlete—but there is still ongoing research into how much these traits were genetic and how much he acquired through training:


  2. Rather than looking at an individual (and Lance Armstrong’s case is particularly complicated), considering categorized groups gives us some statistical purchase. For example, one can ask why African Americans are completely dominant in track sprints from 60 to 800 meters, in professional basketball, and in the cornerback & safety positions in professional football.


    • But there are plenty of environmental differences that could have the same effect here: Race is strongly correlated with poverty, and sprinting and basketball are two sports that required basically no equipment and thus have no economic barrier to entry. There are cultural links that have formed between race and sports—we think of basketball as “Black” and NASCAR as “White”. There is a history of discrimination that has been stronger in some sports than others.

      And then there’s the fact that the racial categories we tend to use are genetically nonsensical. A genuinely sensible genetic hypothesis of athletic performance would require us to use sensible genetic categories; we wouldn’t be asking whether “African American” people perform well, because that category makes no sense; we’d be asking whether Papuans perform well, or Ashkenazi perform well, or people of haplogroup T. If you find a correlation between results and the racial categories we normally use, that almost must be environmental, because there’s no “there there” genetically.


      • You have perhaps proved my point by saying “we think of basketball as black” —– There are more whites playing basketball at the entry level, but as players go from grade school to high school to college and into the professional ranks where the general public watches on TV, the percentage of blacks increases dramatically. No surprise that you think of basketball that way.


  3. How do we resolve the apparent conflict between your statement of paragraph #1 “Race is strongly correlated with poverty” and that of paragraph #2 “…racial categories we tend to use are nonsensical” ?


      • I think as a decent heuristic one can generally assume that the side which does not resort to invoking relativism about reality is the correct one. Thus, when the proponent says a sentence like “The “reality of race” therefore depends more on the definition of reality than on the definition of race” that strongly suggests that the other side has a stronger argument.

        If osteological characteristics seem to cluster more than other traits, that is an interesting fact, and it might even allow for something like a race-based genetic effect on athletic performance (since bone structure is obviously very important for athletic performance). But that still would leave the very serious problem of how it is that the definition of “White” has changed so dramatically over historical time; that clearly can’t be due to changes in the clustering of bone structure traits. Italians do not have radically different bone structure from Anglo-Saxons, yet there was a time not so long ago that Italians were not considered “White”.

        Most importantly, what most people seem to mean when they say the word “race” is not a vague clustering of certain classes of characteristics which are overlapped by clinal variation in other traits; they mean a well-defined, hard-edged genetic categorization of human beings in much the same way as we would define two different species of animal. People are uncomfortable not being able to tell what race someone is, because it violates their concept of how the world is categorized (much as they are uncomfortable not being able to tell what sex someone is). But clinal variation is precisely such that you shouldn’t expect to be able to make harsh categories. It doesn’t bother us that we can’t precisely define whether or not someone is “tall”, because we recognize that height is clinal. If we could conceptualize skin tone the same way, that would be a much more accurate reflection of human variation—and it would be fundamentally incompatible with the concept of “race”. We could start organizing people by their actual haplotypes, but we’d end up with a very different category system, and by the time we worked it all out the question “Why are we doing this?” would loom quite large in our minds.

        As far as political motivations, the fact that race is a social construction has little effect on whether racism exists or whether it is harmful. We don’t need to believe that religions and nationalities are genetic to appreciate that there is discrimination based on nationality and religion, and the fact that height is genetic doesn’t make us worried about whether the fact that basketball players are tall is due to unfair discrimination. Maybe there are some people who believe that they should insist race isn’t real in order to show that racism is wrong, but they are wrong in the same way as people who think they should insist that sexual orientation is genetic in order to show that heterosexism is immoral. The moral argument simply doesn’t hinge on the factual question in that way.

        It does have an effect on how we approach understanding and combating racism, however. When we realize that race is socially constructed, we can think differently about people who are on the borderlines, people who are sometimes perceived as one race and sometimes perceived as another. Are they simply “passing”, somehow betraying their brethren by pretending to be something they aren’t? No; on the contrary they are showing just how arbitrary and useless these categories are in the first place. Realizing that we have socially constructed race allows us to ask the very important question why we socially constructed race, what purpose we thought it served, and this could go a long way toward dismantling it.


    • There is no contradiction. Race is strongly correlated with poverty in the same way and for the same reasons that nationality is strongly correlated with poverty—race and nationality both being social constructions that have real effects on the world only because we make them so. (Perhaps an even clearer example: Money is quite strongly correlated indeed with poverty, but money only exists in our minds.) Race can cause real environmental effects because, like any social construction, it affects our behavior. But it can’t cause real genetic effects because it isn’t genetically well-defined.


  4. Given your replies, how do we understand why African Americans are completely dominant in track sprints from 60 to 800 meters, in professional basketball, and in the cornerback & safety positions in professional football?


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