Letters

Sunday, December 01, 2002
Dear Dr. Pinker . . .
I am writing in response to Steven Pinker's "The Blank Slate" [October]. As a 32-year-old adoptee, I can vouch that you do inherit your personality from your birth parents. I was raised in an ideal home by wonderful people, yet I am nothing like them when it comes to personality. As a matter of fact, that's where we clashed the most. At the age of 30, I finally had the opportunity to be reunited with my birth parents. What a shocker! I was the replica of my birth father in every way except gender. I finally got to see where I got my looks, sense of humor, lack of patience, and mannerisms. This surprised me, as I had always assumed I took after my birth mother. Thank you for confirming what my birth father and I have discussed for the last two years: It's strange how much alike we are, and yet he had nothing to do with my upbringing.

Pamela Danks
—Carlin, Nevada

The first part of your excerpt from The Blank Slate makes a compelling case for the importance of genetic nature—and not just nurture—in our theories of human development. But Pinker's subsequent attempts to assuage fears about "discrimination, oppression, or eugenics" strike me as dubious. It seems Pinker is trying to grapple simultaneously with the consequences of both an individual and a universal human nature. Consider Pinker's assertion that "gay men are likely to have a relatively small nucleus in the anterior hypothalamus." Does the phrase "gay men" here refer to gay men as a group or gay men as individuals? Is there a difference? If not, how can Pinker say that differences among groups are not innate while fully admitting that differences among individuals are innate? Alternately, consider the statement that "convicted murderers and other violent, antisocial people are likely to have a relatively small and inactive prefrontal cortex." Who is to say that this aspect of the universal human nature could not someday be used to justify the prevention of genetic sequences leading to small and inactive prefrontal cortices? A whole bunch of individuals then formally become a "group"—and all of a sudden, eugenics doesn't look that bad.

Keith Turausky
—Tucson, Arizona

Steven Pinker responds: In practice, genetic information is unlikely to predict violence as well as old-fashioned behavioral measures can. Although the genome as a whole affects behavior, the effects come from many genes with small effects interacting in complex ways. When geneticists discover a gene that explains, say, 2 percent of the variation in a trait, they break out the champagne. In contrast, a statistical model with a few variables (such as observers' ratings of a person's aggressiveness, and his history of sadism or bullying) can predict future violence surprisingly well. So the ethical dilemma posed by behavioral genetics in the future—should people with a violence-prone profile be detained even if they have not committed a crime?—is already with us, and we resolve it by finding a defensible trade-off between individual rights and collective safety. Democracies will always face these dilemmas, whether the available predictors of behavior are genetic or something else. Even when genes predisposing certain people to violence are discovered, eugenics will still look bad. If "prevention of genetic sequences" means killing people, it would be bad because killing people is bad. If it means coercing people to have their genomes scanned, to manipulate their embryos, or to have abortions, it would be bad because the citizens of modern democracies shouldn't grant their governments that kind of power over private decisions. If individual rights ever eroded to a point where the government did have such power, an increased understanding of the genetic roots of behavior would be the least of our worries.

I could not sit back and ignore Steven Pinker's "The Blank Slate." First of all, without the evidence he demands of other scientists, Pinker makes such broad generalizations as "In all societies, sex is at least somewhat 'dirty.' " Being the subject of "gossip and teasing" or even "custom" does not necessarily make sex dirty. It could simply make it fun or part of a spiritual or initiatory rite. Pinker goes on to declare that "one of the hazards of sex is a baby," and although he alludes to the sexual revolution of the 1960s and 1970s, he never examines or mentions the reasons for it, among them the invention and availability of the pill and the rise of gay liberation. Pinker assumes his readers are heterosexual, and that none of those people have sex simply to express love or to have pleasure. Pinker totally ignores the existence of gay, lesbian, bisexual, and transgendered people, even in his list of those who are discriminated against "for traits over which they have no control." As a gay man who was born gay, I resent Pinker's simplistic heterosexism.

Clifton Snider, Ph.D.
English and Comparative Literature
California State University, Long Beach

Pinker responds: The scare-quoted word "dirty" was not a judgment by me but a summary from ethnographic surveys of how sex is universally perceived: as more emotionally volatile than other forms of mutual pleasure such as conversation or dining. I'm baffled by the accusation of heterosexism and suspect Dr. Snider has misunderstood my argument. It is not that sex always leads to babies but that it tended to do so among our ancestors, which shaped our sexual emotions today. If people had sex "simply to express love or to have pleasure," they would not prefer sex with attractive partners, jeopardize their intimate relationships by cheating and get jealous when their partners cheat on them, or avoid sex with their siblings, parents, and grandparents. The fact that people's sexual tastes look like strategies for maximizing their reproduction even when they cannot reproduce (such as when they use contraception or have homosexual relations) is precisely my point.

Steven Pinker, while contesting the "blank slate" theory on the grounds that just because it's popular doesn't mean it's true, falls into exactly the same intellectual trap that he admonishes us to avoid. Currently, the most popular sociopolitical model of science is a form of rational materialism, which states that material phenomena (in this case, brain structures) are the cause of observable effects (such as violent behavior). However, the converse argument, that these same material phenomena are actually the effects of nonmaterial causes, such as personal choice or individual effort, is just as likely to be true. Using the criteria laid down in the article, it seems likely that human behavior is not simply a question of nature or nurture but rather a synthesis of both, along with a third force of varying strength: the will of the individual. The greatest failing of Pinker's argument is that it makes not even the briefest mention of individual will as a factor.

David K. Doyle
—New Haven, Connecticut

Pinker responds: Choice, effort, and will are important phenomena, but there is no need to attribute them to some mysterious "third force." They are complex brain processes, arising from an interaction among genes, experience, and chance. We know this because the exercise of will is partly heritable, can be measured in the brain, can be altered by physical causes such as alcohol or neurological damage, and is saddled with quirks and illusions, just like other cognitive faculties.

I enjoyed Steven Pinker's article, but one thing stood out as needing correction. On page 39, he says that "identical twins (who share all their genes) are far more similar than fraternal twins (who share just half their genes)." While part of his statement is true, because identical twins result from a single egg being fertilized by a single sperm, it is not true that fraternal twins (nor siblings born at separate times) always share half their genes. Each parent has 23 pairs of chromosomes that assort independently to form eggs or sperm. Most genes are represented by two copies (called alleles) on a pair of chromosomes. Although the odds are strongly against it, siblings could receive the exact same set of chromosomes (and therefore the same set of alleles) from each parent and be virtually "identical." Conversely, it is possible that siblings (even fraternal twins) would receive completely different chromosomes from each parent and share no alleles in common. It is very likely that fraternal twins will share approximately half their genetic information, but it is not guaranteed.

Carol Crowder
Professor of Biology
—North Harris College, Houston, Texas

Pinker responds: I thank Professor Crowder for pointing out that fraternal twins share half their genes only on average. The probability that the overlap will stray very far from that average is, of course, minuscule. Not only are there 23 random choices of a maternal or paternal chromosome during the assortment process that results in an egg or sperm, but even before assortment, portions of the maternal and paternal chromosomes are spliced together in what is known as crossing-over. This multiplies the number of genetically distinct gametes to even more staggering numbers.

 
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