"Is it nature or is it nurture?" is a damn good question

Some psychologists are confused about this

What is generative AI’s opinion about one of my favorite questions?

Doesn’t hold up well under scrutiny. Thanks, buddy. So much for the idea that AI companions suck up to their users. But to be fair, Claude has provided an accurate distillation of the consensus in my field. It probably assumed I would agree with this consensus.

I don’t.

The traditional way to think about it

One of the great debates in psychology is: What are we born with? How much of the context of our minds is inborn (nature), and how much is due to the environment (nurture)?

The most thoughtful defense of the nurture view came from the 17th and 18th-century philosophers known as the British Empiricists—scholars such as John Stuart Mill, David Hume, and John Locke. One expression of this view, known as empiricism, is from Locke, who popularized Aristotle’s metaphor of the mind as a blank slate. Anything that ends up on that slate—all our knowledge—is inscribed by experience. In the 18th century, Jean-Jacques Rousseau wrote that if a child were born in an adult body, “such a child-man would be a perfect idiot, an automaton, a statue without motion and almost without feeling; he would see and hear nothing, he would recognize no one.” Many behaviorists, some of whom are still around, argue that all that we start with is principles of learning. These principles are the same across species, so there is nothing in the mind of a human baby that you wouldn’t find in a rat or pigeon.

Then there are defenders of nativism, who propose that much of our knowledge and capacities are part of our natural endowment. We are born with them. Philosophers such as Plato explained the existence of innate ideas as the result of souls recollecting knowledge learned in past lives; modern-day nativists think of this as the product of our evolutionary history, encoded in our genes.

When I went to graduate school at MIT, these were the battle lines. My East Coast friends and advisors were on the nativist side, and we mostly did battle with the West Coast empiricists. A Wikipedia article on the East Pole-West Pole divide lists the major players.

Noam Chomsky is weirdly missing from the Wikipedia “nativism” list despite being the most prominent East Coast nativist of all. Here he is, talking about language:

It is a curious fact about the intellectual history of the past few centuries that physical and mental development have been approached in quite different ways. No one would take seriously the proposal that the human organism learns through experience to have arms rather than wings, or that the basic structure of particular organs results from accidental experience. Rather, it is taken for granted that the physical structure of the organism is genetically determined, though of course variation along such dimensions as size, rate of development, and so forth will depend in part on external factors. . . . Human cognitive systems, when seriously investigated, prove to be no less marvelous and intricate than the physical structures that develop in the life of the organism. Why, then, should we not study the acquisition of a cognitive structure such as language more or less as we study some complex bodily organ?

For Chomsky, the idea that language is learned through “accidental experience” is ridiculous. It grows.

The East Coast/West Coast debate was about human universals. Is language innate or learned? What about logical reasoning? Music? Math? Aggression?

A parallel debate concerns human differences. Why are some people wiser than others, funnier, shyer, more neurotic, more violent, more prone to mental illness, and so on?

Again, you get the same battle lines. The empiricists say it’s all environment. The behaviorist John Watson took the Jesuit boast about the power of early education—”Give me the child until he is seven, and I will show you the man"—and ramped it up.

Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select

The nativist response is, not surprisingly, it’s all innate. Our particular natures are inborn. Give me the zygote, and I will show you the man.

Is this a false dichotomy?

Many psychologists nowadays roll their eyes at this. They will tell you that it is naive to say that something is “innate”—or “inborn” or, worse of all, “hard-wired.” The very idea of a strict nature vs. nurture dichotomy is nonsense.

Here’s one example from an article in the journal Trends in Cognitive Science.

The nature–nurture debate, in its traditional dualist form, is all but dead and buried. Converging evidence from genetically sensitive studies, including twin and adoption designs, suggests that the majority of psychological traits and behaviours – from IQ to the likelihood of divorce – are influenced by both genetic and environmental factors.

If you google the title of their article, “Beyond Nature vs. Nurture,” you get this:

Or consider this from an excellent Introduction to Psychology textbook. They tell us that to ask which of the two is more important is like asking

which is more important in defining the area of a rectangle: the length or the width? Development requires both and, in fact, nature and nurture require each other.

(This is presumably where Claude got the example.)

The third example is from a scholar I greatly respect—Joe Henrich. Responding to a paper by Dorsa Amir and Chaz Firestone, which I’ll get to later, Joe writes this on X:

As an evolutionary theorist, I'm partial to explanations that take as given some 'innate structure' that may or may not be modified and adapted ontogenetically via experience. In humans, we adapt ontogentically to culturally constructed environments. In contrast, Dorsa and Chaz want to set up a nature vs. nurture debate. Always a mistake.

To be fair, nature vs. nurture often is a bad question

Sometimes, it really is wrong to ask whether something is innate or learned. It’s going to be a mix.

This is particularly the case for individual differences. Some such differences are due to genes—eye color is a good example of this. And others are all environmental, such as winning a lottery. (If two people buy tickets and one wins, this has nothing to do with the winner’s and loser’s genes.)

But most everything else is a mix. When you look at just about any psychological trait in which people differ—intelligence, extraversion, criminal activity, educational attainment, number of friends, extent of religious belief, favorite foods, mathematical ability, musical ability, and on and on—you’ll find that some of the variation between people is due to genes and some of it is due to environment.

There is a whole field of inquiry—behavioral genetics—which tries to work out the specifics. Sure, differences in intelligence are partly due to genes and partly due to environment. But which genes; what sort of environment? Do parents matter? Are early experiences especially important?

Behavioral geneticists often make claims about how much of human variation is due to these different forces. For instance, it’s often said that genes explain 50% of the variation in intelligence, but there’s fierce debate about this estimate, and some are skeptical about the very idea that one can make precise claims about such things. (After all, the extent to which genes are responsible for a trait varies according to context—as one example of this, intelligence seems to be more heritable for rich children than for poor children.)

What isn’t a matter of debate is that genes and the environment each play a role in explaining the variation in psychological traits. Nature vs. nurture? The answer is both.

Some universals are also a mix of the innate and the learned. Chomsky’s claim about language, cited above, is surely overstated. While some features of language might well be innate in the same sense that the capacity to grow arms and legs is innate, other facets of language are plainly learned. After all, languages differ. They have different phonemes. They have different words. They order words and phrases according to different syntactic rules. And we come to know the phonemes, words, and syntax of our language through attending to the world around us—which isn’t at all analogous to the growth of physical structures like arms and hearts.

But nature vs. nurture is often a great question

Going back to language, you wouldn’t know that the English word used to describe dogs is “dogs” if you hadn’t learned it—that is, if you hadn’t had a specific sort of experience that most people in the world never had.

So much of what’s in your head is the product of learning. How to read. How to play chess. The capital of France. Your age. Your name. All learned.

What’s innate? As I said above, at the very minimum, some capacity for learning must be innate. It’s possible that our current learning capacity was itself learned, but then we must have some earlier capacity for learning that gave rise to this.

If you think that’s all there is to it, you will have the most minimal notion of human nature possible, one that would put a smile on the faces of Locke and Skinner. But most developmental psychologists think the evidence supports a much richer innate endowment.

Let’s return to that Intro Psych textbook. A few pages after they warn you not to pit nature and nurture against each other, they have a section called:

I was born ready: Early capabilities in the newborn.

They point out that if you put your finger in a baby’s palm, the baby will grasp it instinctively. The authors then say, sensibly enough, that this is

a reflex likely inherited from our apelike ancestors who needed to cling to their mothers right from birth as they were carried.

It sure seems like they think it’s innate!

There is evidence for a lot more.¹ Many years ago, the Swiss polymath Jean Piaget proposed that for the first years of life, the baby is a purely sensory creature. At the start of this stage, it perceives and manipulates but doesn’t reason. There’s no sense of time, no differentiation between itself and other people, and, critically, no object permanence.

This last claim has long fascinated psychologists—because it’s so audacious. When a ball rolls behind the dresser, of course, you know it’s still there. What could be more obvious? But Piaget claimed that babies don’t understand that objects exist independently of their actions or perceptions of them. Out of sight, out of mind—literally. This might be why they are so amused by the game of peekaboo. You cover up your face, and then reveal it, and then babies crack up or gasp, and it’s because when you put up your hands, they thought you were gone.

This is a clever hypothesis, but it probably isn’t true. In one classic study done in response to Piaget, babies faced a screen that rotated on the table, moving back and forth as in (a) below. Then, a block is placed on the far side of the table (b). Then, the screen starts rotating back again, as in (c) and (d).

Original Study - Picture credit

Suppose it’s true that for babies, out of sight, out of mind. Then, they should expect that screen to continue moving all the way down because there’s no block to get in its way (d). But when five-month-olds see this actually happen (because you removed the block through a trap door), they look longer. It is as if they are reasoning, “Hey, that’s so weird—there should have been a block there to stop the movement of the screen.” They are more comfortable with the possible event (c), suggesting that they expect the block to still be there.

Or consider this: You see an empty stage. A hand places a single Mickey Mouse doll on the stage. A screen is placed in front of the doll to hide it from view. Then, the hand brings out another Mickey Mouse doll and places it out of sight behind the screen. Then, the screen is removed.

As an adult, you know that one Mickey plus another Mickey equals two Mickeys. Five-month-olds know this too; they are surprised when the screen is removed, and there is one Mickey. They expect two. And this suggests that they appreciate that once an object goes behind the screen, it continues to exist.

Original study and picture credit.

Or consider an example of a different psychological trait, one that I discussed in detail in an earlier post. It concerns the Müller-Lyer illusion, shown below. The red line on top looks longer, but it isn’t.

In a recent paper, Dorsa Amir and Chaz Firestone summarize the debate over the origin of the illusion. One popular view is an empiricist one—it arises because we are raised in environments with certain visual features, such as houses with straight lines and right angles. It’s learned. Amir and Firestone disagree; they think that it’s built into the visual system. It’s hard-wired. In their paper, they make detailed arguments for their nativist view.

In all of these examples, the researchers believe that the capacities in question are part of human nature, not the product of what Chomsky dismissively described as “accidental experience.” Object permanence is likely to be a biological adaptation, pre-wiring the human baby (and, as found in other research, the brains of other animals like newborn baby chicks) to appreciate a world in which objects really do persist over time. The Müller-Lyer illusion is not itself an adaptation but is instead a by-product of how the evolved visual system of humans (and, as found in other research, the visual systems of other animals like guppies) computes the length of objects.

My point is that these innateness claims are perfectly coherent. I think they’re also true, but perhaps as I write this, some clever West Coast neural network researcher is developing a theory that explains how all of this is due to some simple LLM-like system operating before birth. I’d be wrong then: It would turn out that they are not innate; they’re learned.

That would be cool. As I said, nature/nurture debates are among the most interesting of all.

Why do people think nature vs. nurture is a bad question?

One charitable answer is that people often think about individual differences such as introversion, school performance, intelligence, and the like. These are all due to multiple forces, and it would be silly to expect a straight answer to a nature-nurture question. Their mistake is assuming that this has to apply to all human universals, such as object permanence.

A less charitable answer is that some of this is a rhetorical attack by the West Coast Empiricists directed against the nativists. I’ve seen many scholars sneer at the idea that some capacities are innate but then are perfectly comfortable talking about learning, experience, and the effects of the environment. But if you take the interaction argument seriously, it cuts both ways. If it’s dopey to talk about some aspect of language being innate (because that’s as dumb as saying that the width is extra-important in determining the area of a rectangle), then it should be equally dopey to talk about some aspect of language being learned (because that’s as dumb as saying that the length is extra-important in determining the area of a rectangle). The fact that some people don’t see it this way suggests that they either haven’t thought it through or they just like giving the nativists a hard time.

The least charitable answer of all is that some of my colleagues are suffering from bad metaphysics. They start with a true claim:

Everything that’s in our minds wouldn’t be there if it weren’t for both innate structure and experience

As I keep saying, there is no learning (nurture) without initial machinery (nature). Even Skinner would agree that rats learn to run a maze and rocks do not, and this is because only rats have brains capable of maze learning (and legs capable of running). And this initial machinery (nature) typically requires some contact with the world (nurture) to work. Even mental systems like vision often won’t operate without some experience—kittens raised in darkness have significant visual impairments.

Furthermore, life experiences shape just about any innate capacity. As Chomsky, the most extreme nativist of them all, noted when talking about bodily organs, “of course, variation along such dimensions as size, rate of development, and so forth will depend in part on external factors.” To use a cruder example than Chomsky would, the fact that you have a belly is explained in terms of your genes (nature); the size of your belly is influenced, at least in part, by how much pizza you eat (nurture).

Anyway, nobody can doubt that there is continuous interaction throughout development, including specific sorts of interactions that fall under the category of epigenetics.

Where people go wrong is assuming that any of this implies:

There is no such thing as innateness and learning

If you make this jump, you are confusing actual causes (events that bring about an outcome in a non-trivial way) with what philosophers call background conditions (circumstances that enable the outcome to happen but aren’t significant in the same way). Yes, you wouldn’t be able to pick up the rules of pickleball without a lot of innate structure. Those are some of the background conditions. But, still, your knowledge of the pickleball rules is the result of learning about pickleball.

And, while we’re at it, cigarettes cause lung cancer, a deletion of genes from chromosome 7 leads to mild intellectual disability and an outgoing personality, the measles virus gives you spots, and heartbreak makes you cry even though none of this would happen if it weren’t for all sorts of other background conditions in place.

Here, let me tell you a story:

Bill: Oh my God, how did you get the black eye?

Fred: You know that I work across from a middle school? Well, when I get out of my car this morning, some kids were getting off the school bus across the street. And one of them got off and threw a snowball at me and it hit me right in the face. Little prick.

Bill: (Frowns disapprovingly)

Fred: You think I’m too rough on him?

Bill: Yes I do. It sounds like you’re saying that the kid was to blame for your black eye.

Fred: Yes, he threw the …

Bill: Oh, Fred. This is a very reductionist way of thinking. You need to appreciate that there’s a complex interaction going on here.

Fred: A what?

Bill. (Sighs). An interaction. Yes, you wouldn’t have the black eye if it wasn’t for the snowball. But what about the bus driver? If he didn’t drive the bus, the kid wouldn’t have been there. Is the bus driver also a “little prick”? And what about your boss, Fred? You wouldn’t be working there if she hadn’t hired you. No hiring, no black eye. And, hey, what about the meteorological considerations that made it snow that day? No snow, no black eye. And don’t even get me started on your decision to move to this fine city.

Fred: But, but, the kid, he had this nasty gleam in his eye and then he aimed the snowball right at my …

Bill: Fred, I’d like you to take a breath and listen. I’m going to tell you about rectangles.

I hope you’re taking Fred’s side here.

Who cares?

It matters. A good theory of the mind has to distinguish between the origins of a psychological capacity like

color vision (evolved, innate)

and a psychological capacity like

knowing the plots of all of the John Wick movies (not evolved, learned).

and a psychological trait like

being shy around strangers (a subtle combination of the innate and the learned)

So, let’s keep asking, “Is it nature or nurture?” It’s a great question, so long as we appreciate that there are three possible answers: Nature, Nurture, and a combination of both.

1. Some of what follows is based in part on a discussion in my book Psych.