What Anti-Evolutionary Psychologists are Really Worried About
I have a long-standing interest in the nature-nurture debate. My interest is not in trying to figure out whether nature or nurture (inner biology or external environment) is a more important determinant of thought, feeling, and behavior. Everybody knows (or should know) that the answer to that question, in the words of Robert Pirsig, is mu. Mu means "un-ask the question because answering with either of the two choices would produce an incorrect answer."
Do you think the external social environment is more important than inner biology? Okay, let's remove a person's brain and see if the social environment continues to determine that person's thoughts, feelings, and behavior. Do you think that inner biology is more important than the external social environment? Okay, let's rear some children in empty rooms where they have no contact with other people and see if their brains create thoughts, feelings, and behaviors that are similar to children who are raised in normal environments.
Obviously we need all of our inner, biological parts, including our genes, to develop and function normally. Having a normal set of genes is 100% necessary for normal psychological development and functioning. At the same time, we need certain things in our environment to develop and function normally. Without the right kind of food, water, and temperature from our environment, we die. If primates are subjected to social isolation (as the experiments of Harry Harlow dramatically demonstrated), we develop in bizarre ways. Having a normal environment is 100% necessary for normal psychological development and functioning.
So, nature and nurture (inner biology and external environment) are both 100% responsible for psychological development and functioning. To say that one is more important than the other is an intrinsically incoherent position. An analogy can be drawn to baking bread. Which is more important to creating a loaf of bread, the ingredients in the dough or the temperature in the oven? Mu.
If we are all agreed that nature and nurture are both indispensably important to psychological functioning, then it would seem that the debate should be over. But, oddly, the debate rages on! And that is what interests me about the nature-nurture debate: What, exactly, is motivating folks to argue that nature or nurture is more important when both are clearly equally important?
There is at least one possibly reasonable way to say that genes or environment are relatively more important for a particular psychological trait, found in the concept of heritability in behavioral genetics. Heritability is a statistical estimate of the percentage of variability in an observed trait that can be explained by genetic variability. For example, a study by Alford, Funk, and Hibbing on the heritability of political attitudes reports that the heritability of attitudes toward school prayer is .41, which means that 41% of the differences in measured attitudes toward school prayer are estimated to be due to genetic differences. This figure is less than 50%, which might lead some to conclude that social environmental influences are more important than genes in determining your attitudes toward school prayer.
The trouble is that this is a completely erroneous way to make deductions about the importance of genes from heritability coefficients. Heritability merely describes the observed differences in a group of people that can be accounted for by genetic differences. Heritability does not describe exactly how genes contribute to a trait in an individual. Presumably, genes play an important role in our having two arms and two legs. There are several genetic defects that cause people to be born without limbs. Nonetheless, if you were to conduct a behavioral genetics twin study on limb number, you would find that the heritability of having two arms is zero. This is first of all because there is very little variability in the number of arms across people. Most people have two arms. Heritability describes the amount of differences in an observed trait that can be accounted for by genetic differences. If there are little differences in an observed trait, there is little to account for. Furthermore, for the rare cases of people with one arm, most are due to environmental events such as accidents. Consequently, the heritability of the number of arms we have is zero, even though genes are important for the normal development of two arms. At the same time, environments are also important. Whether or not you work near dangerous machinery can have a powerful influence on how many arms you have.
The observation about heritability being low when people do not differ much on a trait suggests that heritability coefficients that are computed for groups that differ in variability will produce heritability coefficients of different sizes. If, for some reason, your sample contained mostly people who are relative extraverted, the heritability coefficient would be lower than if your sample contained more variation in introversion-extraversion. Likewise, if you have a sample where environmental factors that influence personality vary greatly across families (e.g., different childrearing techniques), estimates of environmental influence will be greater than for a sample where there is little environmental influence (everyone rears their children the same). Consequently, we cannot say that the "actual" heritability for a particular trait is a specific number such as .41. Different samples will have different amounts of variability in the trait measured and in the environmental influences, producing different heritability estimates.
Heritability estimates can also depend on the type of measures and data used in the study as well as specific methods for estimating heritability. Given that heritability coefficients can vary depending upon the sample and the type of data collected, it is less important to focus on the specific numerical value for heritability (whether it is .3 or .4 or .5) than to realize that a surprising number of traits have shown substantial heritability. Who would have guessed that the heritability of attitudes toward school prayer is as large as 40%? Virtually all personality traits-the building blocks of who we are-have estimated heritabilities in the 40-50% range.
The bottom line is that heritability coefficients that estimate the percentage of differences in a trait that can be statistically accounted for by genetic differences don't really indicate the relative importance of your genes and environment in determining who you are. Regardless of the heritability of limblessness, one person can be limbless due to genes and another, due to an industrial accident. And limblessness is a simple, either/or case in which we actually know the mechanisms by which one has less than four limbs. Most psychological traits are a matter of degree, and we do not know exactly how genes and environments interact to create traits. All we can be assured of is that both are involved and we cannot say that one is more important than the other.
Which leads back to the question, just why would someone proclaim that either nature or nurture is more important? Actually, I am exclusively interested in why people say that nurture is more important than nature, because I have not seen the opposite claim-that nature matters more than nurture-from behavioral geneticists and evolutionary psychologists. Invariably, biologically-inclined psychologists emphasize that both factors matter rather than saying one is more important than another. At most, they have argued that biological factors have not been taken as seriously as they should be, not that they are more important. Therefore, what needs to be explained is nurturism-the belief that nurture is somehow more important than nature or even that biology does not matter at all.
I have an admittedly speculative hypothesis involving the motivation underlying why someone would say that nurture matters more than nature. The explanation is very similar to the one I proposed for explaining why some people hate the idea of personality traits (see Trait-Haters, Inc.). My hypothesis is that nurturists mistakenly believe that biology implies immutability. They therefore believe that if genes are involved in immoral behaviors such as lying, promiscuity, infidelity, rape, and murder, this leads to the intolerable conclusion that the human condition cannot be improved. (The similar fear from trait-haters is being trapped and limited by their traits.) I would make two responses to the misconception that biology implies immutability.
The first response to such a misconception would be to point out the myriad ways in which biology implies change rather than lack of change. Evolution through natural selection is all about change. Also, as individual organisms develop from single cells to adults, they undergo astonishing physical changes. Furthermore, at any moment in time, our bodies are in continuous flux, with our various systems interacting with each other and with the external environment. Underlying many of these larger, changing processes are changes occurring at the genetic level, with DNA causing changes in cell chemistry through the increasing or decreasing production of proteins. Biology does not imply immutability.
The second response I would make, is that if we want to improve the human condition, we need to understand exactly how biology is involved in our psychological makeup. It does not help to deny any role for biology and imagine that somehow nurture makes everything happen. The hope of professional evolutionary psychologists is to improve the human condition by acquiring an accurate understanding of evolved human nature. And yet evolutionary psychologists find themselves constantly under attack, not just for getting facts wrong or having inadequate explanations, but for actually making the world a worse place, using their ideas to justify immoral behavior.
Take, for example, a recent blog post by Darcia Narvaez, Evolutionary Shockology and Human Nature. In this post, Narvaez claims that evolutionary psychology "tends to push a negative and cynical worldview" and claims that "murder, war, rape" are "a necessary part of human existence." She blames evolutionary writer Richard Dawkin's book, The Selfish Gene, for the misbehavior of Enron sociopath Jeff Skilling, completely ignoring the possibility that Skilling's genetic makeup had something to do with his outrageous behavior (see Barbara Oakley's fascinating book on this subject.) Narvaez compiles a list of criticisms of evolutionary psychology, organized under headings such as "Killing is not in our genes," "Rape is not in our genes," and "War is not in our genes." She incites a follow-up poster to say "I think that EP has got out of hand, especially when people use it as excuses to be plain old jerks."
Do evolutionary psychologists really believe that we cannot improve the human condition and that we want to justify murder, war, and rape? Do we publish studies that we hope people will use as excuses to be jerks? Narvaez clarifies in a follow-up comment to her post that she was criticizing only a subset of evolutionary psychologists: "It's the subset like Pinker and others who assume that humans are selfish, violent and sex-crazed that are being criticized." Somehow, she seemed to be unaware (until a follow-up commenter mentioned it) that Steven Pinker, a leading evolutionary psychologist, has been doing a book tour for his latest publication, The Better Angels of Our Nature. In this book, Pinker describes how we have been experiencing a decrease in violence over the last several thousand years. (If you want a quick summary, see his interview with Colbert.) Nurturists are amazingly blind to the fact that evolutionary psychologists are very interested in reducing immoral behaviors, not rationazing them!
Then again, perhaps I should not be surprised. Nurturists seem to be incapable of recognizing that the bogey-men that they fear simply do not exist.