by Mark Pagel
MADE OR BORN?
THERE IS no reason to restrict our thinking to artistic, sculptural, and musical abilities; it is just that they have left a remarkable trail of artifacts. Now, whether we believe that human culture has cultivated differences among us, we really have only two choices to understand our obvious variety of talents: are we, in a word, “made” or “born”? The latter view says that genes are the dominant force in our lives, and it is our genetic inheritance that influences what we become, and why we differ from each other. Stacked against this notion is the point of view that says our environments make us what we are. Our differences might have little if anything to do with our genes, but much to do with upbringing and opportunities that arise by chance. People come to their various stations in life by good or bad luck, social immobility, long-lived cultural influences, and teaching and training.
No one doubts that children’s early learning and social environments and the opportunities these provide strongly influence their eventual educational and economic attainments. But the truth, as with so many questions that pit nature against nurture, almost certainly lies somewhere in between the two extremes. In fact, modern genetic and behavioral studies are revealing that we are neither made nor born. Rather, these studies show that what we are born with—our genetic endowment—can exert a powerful influence on what environments we are attracted to: someone good at kicking balls is attracted to sports, someone good at music is attracted to music, someone good at mathematics is attracted to working with numbers. And this brings us full circle to the theme of this chapter. We have seen how human culture uniquely provides a range of opportunities that might encourage genetic variety to be maintained in our ranks (not least in sports and music)—genetic varieties that would otherwise lie dormant—by providing the outlets that attract those with differing talents and skills.
Animal breeders are quietly aware there are wide differences among animals in temperament and behavior that they can encourage or suppress through careful breeding. These are genetic differences, but there is reluctance bordering on zealotry to acknowledge the possibility of genetic differences related to disposition or performance among humans. And yet, it turns out that a substantial portion—often 50 percent or more—of the differences among people in just about anything that can be reliably measured seem to be attributable to differences in their genes, at least insofar as these can be measured by looking for similarities between parents and offspring. The list includes physical traits, reaction times, spatial reasoning, verbal and mathematical intelligence, attitudes, personality, and even occupational, social, and religious preferences. No one suggests there is a gene for your religious preference, or for your particular occupation, for that matter; but temperamental, intellectual, and personality differences that do have a genetic origin might influence your attraction to religion or to a particular occupation.
Fifty percent is a high figure, but one that also of course allows for a large—50 percent—input from the environment. Still, we need to interpret this statement carefully. When newspapers and televisions quote scientists who say it is meaningless to ask which is more important, genes or environment, because “all genes require an environment in which to express themselves,” these scientists are right but saying something misleading. To suggest that genes influence a behavior or characteristic is not the same as saying that feature is determined by genes. Rather, it says that two people, one with a particular gene or set of genes and one without, and each brought up in typically human environments, will on average differ. The proviso “typically human environments” is important. If it were possible to rear people in identical environments right down to the smallest details, then any and all differences among them would be attributable to their genes. On the other hand, if we were to rear people in extreme environments that overwhelmed any influence of their genes, then the genetic contribution to how they turned out would appear negligible. For instance, our genes have not evolved in the environment of being a toad or mushroom. Were we to attempt to raise a group of us as mushrooms (or even toads), any genetic differences among us would be swamped by the utter unsuitability of this unfamiliar upbringing; indeed, most of us, if not all, regardless of our genes, would simply die.
The skeptical stance that it is meaningless to ask about genes versus environment conveniently ignores that our genes have evolved over very long stretches of time in what has been a fairly predictable and typical human environment, beginning with life in utero. Yes, some of us trace our ancestry back to people who lived in hot environments and others cold, or some of us have enjoyed enriched environments during our lifetimes while others have suffered deprivation; but all of us throughout history have faced a similar set of challenges of staying alive and prospering as a human, and not as toads or mushrooms. These are the challenges that our genes, having been shuffled around among the bodies of our ancestors, will have had to adapt to. And so when we study large numbers of people, we hope these environmental differences get averaged out, leaving something we can interpret as the effect of a gene in a typical human environment.
Bearing these points in mind, we can try tentatively to interpret whether the variety we see around us might bear the signature of genes. The psychologist Thomas Bouchard undertook beginning in the 1970s a now famous series of studies of identical twins who had been reared apart owing to adoption. Identical twins reared apart share all of their genes, but not their environments, and so can help to reveal the relative importance of one over the other. If genes play only a small role, then we would not expect twins reared apart to be similar. But study after study shows that they are—and often strikingly so—on measures of intelligence, aptitudes, spatial reasoning, and features of personality. Sometimes the similarities among identical twins are unnerving. Bouchard reported a pair of identical twin sisters reared apart who were both afraid of water. Even though they had never met, they both recounted tales of being taken to the seaside, and when approaching the water, both recalled turning around and backing in; twin brothers reared apart both grew up to be firefighters, and both were captains of their firefighting teams; two sisters reared apart both had a habit of wearing seven bracelets.
Bouchard’s and others’ twin studies are criticized because twins who are reared apart are frequently adopted by families of similar backgrounds, even if unwittingly. But we can compare identical and non-identical twins who have been reared apart. Non-identical twins are no more similar genetically than ordinary brothers and sisters. When these two cohorts are compared, the identical twins reared apart routinely prove to be more similar than the non-identical twins reared apart, implying a strong role for genes. It also seems that the influence of genes becomes stronger in environments to which they are suited, as if finding the right environment reveals the effects of genes. An adopted child with musical talent who just happened to be brought up in a musical environment would achieve more than someone with a similar set of genes in a non-musical environment, and more than a non-musical person brought up in a musical environment. If you think this is just common sense, it is also a statement of culture (a particular home environment) unmasking innate abilities. And it is something that would not have been lost on prehistoric cave painters handed the latest new ochre pigmentation or a sculptor handed new carving tools.
Still, we must be careful. Bouchard’s studies do not specify in advance what sorts of personality similarities and differences are expected, and so stories of how two people back into water, or how two brothers both became fire captains might just be quirky or unusual things that emerged by chance from trawling through hundreds of answers given in interviews. Indeed, years ago a colleague of mine undertook a study in response to Bouchard’s work that he sardonically called “similarities among perfect strangers reared apart.” He got people to fill in questionnaires asking them about likes and dislikes, habits, personality traits, educational background, and so on. Then he randomly sorted the respondents into pairs and compared their responses. As
might be expected, if you ask any two people enough questions, there will be something unusual they agree upon, and he found them. Two “perfect strangers” might have shared the same favorite opera, the same favorite song, or the same hobby (maybe perfect strangers reared apart are nevertheless reared in similar environments!). But this should not be taken as a refutation of the main body of Bouchard’s work. Identical twins reared apart are more similar to each other on a wide range of measures of intelligence, personality, temperaments, and morphology than non-identical twins reared apart, and they in turn are more similar than random pairs of strangers.
For an evolutionist, the intrigue in Bouchard’s work is that we are able to see any real genetic variety at all in these measures. Remember that natural selection’s propensity is to use up differences among individuals, as our example of antelopes, songbirds, and lions shows. And, indeed, in many of our traits, such as how many fingers we have, or how many arms and legs, there is no variation, at least beyond occasional genetic abnormalities. Even among all the 5,000 or so different mammal species, there is no variety in the number of neck vertebrae: we all have seven, yes, even the giraffes. They build their startlingly long necks not by adding vertebrae but by merely elongating those they, and we, have. Equally, one won’t lose many bets by saying a person has ten fingers or ten toes. Natural selection has all but erased differences among us in the ways that our genes give rise to the numbers of arms and legs or fingers and toes we have. Why, then, hasn’t natural selection erased differences in height, or running speed, musical talent, personality, or mathematical and spatial ability?
Normal numbers of fingers and toes illustrate an important and often misunderstood feature of natural selection. The term heritability has a technical meaning, referring to how much of the variety among a group of people on some trait—such as height or hair color or mathematical ability—can be attributed to differences in their genes. Heritability is a property of a group of people, not of an individual. Traits that are highly heritable are those that differ among individuals, and those differences are preserved in offspring from one generation to the next owing to the genes they inherit: height is heritable because tall parents tend to produce taller than average children, and vice versa. Intelligence is heritable because more intelligent parents tend to produce offspring of higher than average intelligence, and vice versa. If there is no variety among the people in the group, then there are no differences for genes to explain, and so we say there is no genetic heritability of that trait. Number of fingers and toes is a trait that does not vary among individuals, and so we say it is a trait that lacks heritability. Even so, numbers of fingers and toes is inherited because it is caused by genes—it is just that those genes don’t differ among us.
But here is the surprise. Standard genetic theory tells us that genetic traits with high heritability (lots of differences among individuals) are not strongly linked to our ability to survive and reproduce. An amusing pastime in national art galleries is to identify the long noses, thin lips, or so-called aristocratic chins that crop up over and over in the Old Masters’ paintings of the generations of a nation’s ruling class. These are heritable traits and they indeed differ among individuals. But we don’t think they tell us much about someone’s chances of surviving. On the other hand, the same genetic theory tells us that the traits we think are most important to our ability to survive and reproduce, what is sometimes called our fitness, are least likely to vary among individuals. This is because natural selection weeds out the differences among us on the traits that are vital to our survival and reproduction. Try grasping a heavy round object such as a metal pipe or a glass filled with water while not using one of your fingers and you will discover that your five fingers are well suited to grasping (although one could counter this by saying that these objects have evolved culturally to be shapes we can grasp, and that if we had just three fingers these objects would have different shapes).
This conclusion leaves us in an unexpected place. Do we really believe that the heritable differences in language or mathematical ability, or differences in musical or artistic ability, have somehow not been important for promoting our survival and reproduction? Perhaps they are not, and our genetic variety does not confer any meaningful differences among us. But if we believe that these heritable differences have conferred meaningful differences in our abilities, then only two plausible answers can be given for the existence of our genetic variety. One is that the purposes the genes serve have arisen only so recently in our history that they are still sweeping through human populations, and eventually we will all have them just as we all have ten fingers and ten toes. Thus, perhaps certain mathematical, musical, and spatial abilities and certain aspects of our personalities only became important once human societies grew and became complex. Some of us have, for example, inherited genes for mathematical ability already, and if we wait long enough, all of us will eventually have the genes that confer these abilities.
A second answer emerges from thinking of the variety we observe in our traits as arising from the different roles or strategies the social environment of culture has made available. If there is no single best way of being a human, then natural selection would not “use up” genetic differences among us, the way it uses up, for example, differences in running speed among gazelles. Instead, our genetic variety in things like mathematical, architectural, analytical, linguistic, mechanical, engineering, creative, oratorical, physical, and artistic abilities would be maintained because people with differing genetic makeups have filled the different roles that our many and diverse cultural innovations have created throughout our history.
ALTERNATIVE BUT EQUALLY GOOD STRATEGIES
IT IS important to emphasize that this is not an argument for the superiority of some combinations of genes. It says that different combinations of genes make people suited to tasks that have been approximately equally successful throughout our history in promoting our survival and reproduction. Were they not, the less successful combinations of genes would have disappeared. One of the more subtle and powerful ideas to emerge from evolutionary biology in the past fifty years or so is the notion of evolutionarily stable strategies. We can think of a strategy as a behavior you adopt in your encounters with others. An evolutionarily stable strategy can be roughly defined as a strategy that when enough individuals adopt it, it cannot be bettered by any other strategy. A simple example might be your behavior in standing in line to board a train or bus. If you are polite, others will crowd in front of you and you won’t get a seat. So, being polite is not a stable strategy for getting a seat because others will outcompete you. To counter this, you could become pushy and now you probably will get a seat. But is being pushy a stable strategy? Well, if everyone adopts this strategy, fights might break out and you could get injured. Now it might be better to be polite—you won’t get a seat but at least you won’t get hurt.
In fact, this made-up scenario describes a situation that evolutionary biologists call the Hawk-Dove game, and it turns out that neither the Hawk nor the Dove strategy is the “best,” because whenever one of them becomes popular, the other can either take advantage of it or obtain higher rewards. So, maybe there is some intermediate “self-interested but not too pushy” strategy—we could call it prudent—that gets you a seat much of the time, but allows you to avoid fights. Maybe you position yourself near to where the train door will open, or you crowd in just a little bit to get in front of someone, but not so obviously that they become indignant and accost you. This strategy of prudence could have a higher payoff than either of the others, and if so it would become the one that most people would adopt. It could even be the evolutionarily stable strategy if it avoided the injuries the Hawks get and simply stepped in front of the Doves.
The simple parlor game of rock-scissors-paper is a game of stable and alternative strategies in which all three exist simultaneously. Each strategy (rock, scissors, or paper) can win against just one other, and each strategy beats a dif
ferent other strategy (rock beats scissors, scissors beat paper, but paper beats rock). Knowing this, one way to approach the game is to adopt a mixed strategy in which you randomly play each strategy one third of the time. This will produce a win on average once in every three encounters. If you deviate from this and play, say, scissors over and over, someone who switches to playing rock will beat you, and your payoffs or “fitness” will fall. Alternatively, players could adopt pure strategies: we could imagine thirty people playing the game, with ten assigned to play each strategy and only that strategy. If they mix amongst each other at random, each person will win, on average, one third of the time. If someone deviated from their strategy, say a rock became a scissors, the people playing rock would begin to do better because they would meet people playing scissors just that little bit more often.
Males of the common side-blotched lizard (Uta stansburiana) play a pure strategy version of the rock-scissors-paper game in their competition to mate with females. Each male has one of three different genetically determined mating strategies. Polygynous males are large in size and can therefore control large territories. By controlling these large territories, the polygynous males can guard and exclusively mate with a number of females. The polygynous males can even take females away from smaller monogamous males which, having smaller territories, attempt to guard just a single female. But the polygynous males don’t ever take over completely. A small, sneaky male can take advantage of the polygynous males by snatching a liaison with one of his females when the polygynous male is not watching. On the other hand, the sneaky tactic does not work against the monogamous males because they can guard their single female. As with the parlor game, each one of these strategies can “beat” a different one of the others, and whenever one becomes too numerous, one of the others will take advantage of it.
