Nature Versus Nurture Quotes

“The propositions that accompany most of the chapters . . . are not as snappy as I would prefer—but there’s a reason for their caution and caveats. On certain important points, the clamor of genuine scientific dispute has abated and we don’t have to argue about them anymore. But to meet that claim requires me to state the propositions precisely. I am prepared to defend all of them as “things we don’t have to argue about anymore”—but exactly as I worded them, not as others may paraphrase them.

Here they are:

1. Sex differences in personality are consistent worldwide and tend to widen in more gender-egalitarian cultures.

2. On average, females worldwide have advantages in verbal ability and social cognition while males have advantages in visuospatial abilities and the extremes of mathematical ability.

3. On average, women worldwide are more attracted to vocations centered on people and men to vocations centered on things.

4. Many sex differences in the brain are coordinate with sex differences in personality, abilities, and social behavior.

5. Human populations are genetically distinctive in ways that correspond to self-identified race and ethnicity.

6. Evolutionary selection pressure since humans left Africa has been extensive and mostly local.

7. Continental population differences in variants associated with personality, abilities, and social behavior are common.

8. The shared environment usually plays a minor role in explaining personality, abilities, and social behavior.

9. Class structure is importantly based on differences in abilities that have a substantial genetic component.

10. Outside interventions are inherently constrained in the effects they can have on personality, abilities, and social behavior.”
― Charles Murray, Human Diversity: The Biology of Gender, Race, and Class

“Correlation and causality. Why is it that throughout the animal kingdom and in every human culture, males account for most aggression and violence? Well, what about testosterone and some related hormones, collectively called androgens, a term that unless otherwise noted, I will use simplistically as synonymous with testosterone. In nearly all species, males have more circulating testosterone than do females, who secrete small amounts of androgens from the adrenal glands. Moreover, male aggression is most prevalent when testosterone levels are highest; adolescence and during mating season in seasonal breeders. Thus, testosterone and aggression are linked. Furthermore, there are particularly high levels of testosterone receptors in the amygdala, in the way station by which it projects to the rest of the brain, the bed nucleus of the stria terminalis, and in its major targets, the hypothalamus, the central gray of the mid-brain, and the frontal cortex. But these are merely correlative data. Showing that testosterone causes aggression requires a subtraction plus a replacement experiment. Subtraction, castrate a male: do levels of aggression decrease? Yes, including in humans. This shows that something coming from the testes causes aggression. Is it testosterone? Replacement: give that castrated individual replacement testosterone. Do pre-castration levels of aggression return? Yes, including in humans, thus testosterone causes aggression. Time to see how wrong that is. The first hint of a complication comes after castration. When average levels of aggression plummet in every species, but crucially, not to zero, well, maybe the castration wasn't perfect, you missed some bits of testes, or maybe enough of the minor adrenal androgens are secreted to maintain the aggression. But no, even when testosterone and androgens are completely eliminated, some aggression remains, thus some male aggression is testosterone independent. This point is driven home by castration of some sexual offenders, a legal procedure in a few states. This is accomplished with chemical castration, administration of drugs that either inhibit testosterone production or block testosterone receptors. Castration decreases sexual urges in the subset of sex offenders with intense, obsessive, and pathological urges. But otherwise, castration doesn't decrease recidivism rates as stated in one meta-analysis. Hostile rapists and those who commit sex crimes motivated by power or anger are not amenable to treatment with the anti-androgenic drugs. This leads to a hugely informative point. The more experience the male had being aggressive prior to castration, the more aggression continues afterward. In otherwise, the less his being aggressive in the future requires testosterone and the more it's a function of social learning.”
― Robert M. Sapolsky, Behave: The Biology of Humans at Our Best and Worst

“Our minds have been built by selfish genes, but they have been built to be social, trustworthy and cooperative. That is the paradox this book has tried to explain. Human beings have social instincts. They come into the world equipped with predispositions to learn how to cooperate, to discriminate the trustworthy from the treacherous, to commit themselves to be trustworthy, to earn good reputations, to exchange goods and information, and to divide labour.”
― Matt Ridley , The Origins of Virtue: Human Instincts and the Evolution of Cooperation

“It is through the child’s eyes and ears, not genes, that he or she gets, from his or her parents, things such as humility and intolerance.”
― Mokokoma Mokhonoana

“People aren’t born evil.”
― A.D. Aliwat, In Limbo

“When Bouchard’s twin-processing operation was in full swing, he amassed a staff of eighteen—psychologists, psychiatrists, ophthalmologists, cardiologists, pathologists, geneticists, even dentists. Several of his collaborators were highly distinguished: David Lykken was a widely recognized expert on personality, and Auke Tellegen, a Dutch psychologist on the Minnesota faculty, was an expert on personality measuring.
In scheduling his twin-evaluations, Bouchard tried limiting the testing to one pair of twins at a time so that he and his colleagues could devote the entire week—with a grueling fifty hours of tests—to two genetically identical individuals. Because it is not a simple matter to determine zygosity—that is, whether twins are identical or fraternal—this was always the first item of business. It was done primarily by comparing blood samples, fingerprint ridge counts, electrocardiograms, and brain waves. As much background information as possible was collected from oral histories and, when possible, from interviews with relatives and spouses. I.Q. was tested with three different instruments: the Wechsler Adult Intelligence Scale, a Raven, Mill-Hill composite test, and the first principal components of two multiple abilities batteries. The Minnesota team also administered four personality inventories (lengthy questionnaires aimed at characterizing and measuring personality traits) and three tests of occupational interests.
In all the many personality facets so laboriously measured, the Minnesota team was looking for degrees of concordance and degrees of difference between the separated twins. If there was no connection between the mean scores of all twins sets on a series of related tests—I.Q. tests, for instance—the concordance figure would be zero percent. If the scores of every twin matched his or her twin exactly, the concordance figure would be 100 percent. Statistically, any concordance above 30 percent was considered significant, or rather indicated the presence of some degree of genetic influence.
As the week of testing progressed, the twins were wired with electrodes, X-rayed, run on treadmills, hooked up for twenty-four hours with monitoring devices. They were videotaped and a series of questionnaires and interviews elicited their family backgrounds, educations, sexual histories, major life events, and they were assessed for psychiatric problems such as phobias and anxieties.
An effort was made to avoid adding questions to the tests once the program was under way because that meant tampering with someone else’s test; it also would necessitate returning to the twins already tested with more questions. But the researchers were tempted. In interviews, a few traits not on the tests appeared similar in enough twin pairs to raise suspicions of a genetic component. One of these was religiosity. The twins might follow different faiths, but if one was religious, his or her twin more often than not was religious as well. Conversely, when one was a nonbeliever, the other generally was too. Because this discovery was considered too intriguing to pass by, an entire additional test was added, an existing instrument that included questions relating to spiritual beliefs.
Bouchard would later insist that while he and his colleagues had fully expected to find traits with a high degree of heritability, they also expected to find traits that had no genetic component. He was certain, he says, that they would find some traits that proved to be purely environmental. They were astonished when they did not. While the degree of heritability varied widely—from the low thirties to the high seventies— every trait they measured showed at least some degree of genetic influence. Many showed a lot.”
― William Wright, Born That Way: Genes, Behavior, Personality