Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

  * For those who care, the number of unique transcriptional profiles for n number of genes is (2n)−1, not counting the state where no genes are being transcribed. So plug the approximately 20,000 human genes into the equation, and you get a gargantuan number of possible transcriptional profiles.

  * “Epigenetic” technically refers to altering the regulation of genes, rather than the sequence of genes. Therefore a transcription factor activating some gene for ten minutes counts as epigenetic as well. When neuroscientists talk of the “epigenetics revolution,” however, they’re almost always referring to the long-lasting mechanisms discussed here.

  * Note that Lamarck was talking about the concept of species evolution long before Darwin and Wallace. The latter two didn’t invent the idea of evolution; rather, they figured out how evolution works, namely by natural selection.

  * And as a brilliant counterstrategy, some parasites use transposons to shuffle the DNA coding for their surface proteins every few weeks. In other words, just as the infected host is building up stocks of antibody to recognize the surface protein, the parasite switches identities, making the host immune system start all over.

  * There have even been reports of heritability of intelligence in chimpanzees.

  * I was pleased to see this study. Numerous studies, stretching back decades, have attempted to uncover the biological roots of sexual orientation; the earlier literature overwhelmingly came with the political agenda of trying to figure out what is biologically “wrong” with homosexuals. Thus, it was about time for people to study what’s wrong with homophobes.

  * Yeah, I’m shorter than average.

  * Historically, the most hyperoxygenated criticisms of behavioral genetics as a discipline have come from nongeneticists questioning the motives and hidden sociopolitical agendas behind behavior genetics findings. It is historically justified to conclude this at many junctures; however, it’s utterly inapplicable to the behavior geneticists I know. The next chapter will look at a related version of a “there’s a hidden agenda” controversy.

  * And roughly similar conclusions can be reached concerning end points like weight, height, BMI, and various metabolic measures.

  * Whether MZ twins wind up as mono- or dichorionic depends on when the new embryo divides.

  * Not always—there are some truly weird mechanisms of gene transmission involving “imprinted genes” that violate this, but we’re ignoring that.

  * I thank an excellent student assistant, Katrina Hui, for help in this area.

  * Although many purists in the field would say that we don’t actually inherit a trait; we inherit the material needed to construct a trait.

  * This next section has been heavily influenced by the writings of the geneticists Richard Lewontin of Harvard and David Moore of Pitzer College and the science writer Matt Ridley.

  * Genetics savants will note that I’ve simplified things here by ignoring heterozygosity; it doesn’t matter.

  * Here’s a cool example pointed out to me by a colleague, Bud Ruby. All those twin studies generate heritability scores, indicating the strength of genes in explaining individual variation. But those studies, by definition, have eliminated an important nongenetic source of variation—birth order.

  * There has been some controversy about the replicability of this immensely important observation, and I’ve followed it closely. When considering only the carefully done studies with adequate sample sizes and clearly and narrowly defined end points, I believe that it’s been amply replicated.

  * A subtle point for which I thank Stephen Manuck of the University of Pittsburgh: This example represents an exception to the rule that heritability scores go down as you study a trait in more environments. If you started by studying only low-SES individuals, you’d generate a very low heritability score (~10 percent). Thus, if one studies both low- and high-SES subjects (the latter with a high heritability score of about 70 percent), the score will rise.

  * Harking back to how the noncoding regulatory regions of the genome are at least as important as regions that code for genes themselves, the 5HTT variants do not differ in the DNA sequence of the gene but rather in the sequence of a promoter for the gene. As a result, the two variants differ in their sensitivity to a transcription factor, and thus in the amount of transporter protein made.

  * Again, the variation in the DNA sequence was not in the MAO-A gene but in its promoter.

  * Part of what may explain the “warrior gene” frothiness is the “aggressive” variant being found at a high rate among Maori populations and traditional Maori culture having very high rates of warfare. Nonetheless, it is far from the case that every Maori individual with the “warrior” variant is highly aggressive, or that every highly aggressive Maori has the warrior variant.

  * Control subjects had the task of unscrambling jumbled strings of words into coherent phrases. The religion-prime group did the same with word strings that contained religious terms.

  * For aficionados: The testosterone receptor contains what is called a polyglutamine repeat—a stretch of the protein where the same amino acid, called glutamine, is repeated. Importantly, there is tremendous variability among people as to how many glutamine repeats there are; the fewer, the more potently the androgen receptor works. Recall that receptors for steroid hormones like testosterone work as transcription factors, and proteins that have polyglutamine repeats are often transcription factors.

  * And, following that logic, if a trait associates with a particular version of an SNP in the promoter of a gene, you’ve just gotten a hint that the regulation of the gene (as opposed to the gene itself) may be involved in that trait. As an example, the gene for one type of serotonin receptor contains an SNP in the third base of the codon coding for the thirty-fourth amino acid in the protein, and one of the variants of that SNP is associated with responsiveness to a particular drug in schizophrenics.

  * For lovers of details: Note that the GWAS and microarray approaches are usually telling different things. In the former you are looking for genes that have a variant that is associated with whatever disease or behavior you’re studying. In microarray studies you’re looking for genes whose expression profiles are associated with the disease or behavior.

  * More scientific lingo—pass a big fishing net through a stretch of the ocean, and see what you wind up catching.

  * This would be if there is a gene that has an SNP that is unbelievably powerfully associated with something, but the alternate letter only occurs in a thousand humans. That will be missed with current GWAS.

  * Note that the other reliable sex difference in cognition, namely better reading performance by girls than by boys, doesn’t disappear in more gender-equal societies. It gets bigger.

  * In reading about Americans versus East Asians in this section, and Americans versus other cultures in later sections, you’ll realize that in some ways it’s Americans (and Western Europeans) versus the rest of the world in many cultural ways. They are just plain “WEIRD”—Westernized, educated, industrialized, rich, and democratic.

  * These are tough studies to pull off, as neuroimaging is a bit of an art in addition to a science, and being able to quantitatively compare data derived from two scanners and scanning protocols on opposite sides of the globe is challenging. The alternative—having subjects from both cultures studied in the same scanner—is challenging as well; those aren’t going to be representative subjects, since half of them are probably international students—connected, well off, and adventurous enough to be in an American college town, volunteering for a Psych 101 study.

  * The United States was not without labor-intensive agriculture historically. But rather than solving that with collectivism, it solved it with slavery.

  * I have no idea if rice roots actually run deep, but the metaphor was begging to be written.

 
* Obviously, no individual actually migrated that far—the slow creep of migration southward in the Western Hemisphere took millennia.

  * For genetics fans with more of a background than chapter 8, the near-zero incidence of 7R means that in these cultures there isn’t even any benefit to heterozygous versions of 7R.

  * As noted earlier, within a few generations of immigration, East Asian Americans are typically as individualist as European Americans. This raises the question of whether East Asians who chose to immigrate had a higher frequency of 7R than East Asians in general (one might also wonder whether there is a higher incidence of 7R in the wheat-growing regions of China than in the rice districts). Unfortunately, according to Kenneth Kidd, no one knows about either.

  * Another striking difference in gene variant frequencies concerns the gene coding for the serotonin transporter, which removes serotonin from the synapse and which, as we saw in the last chapter, is associated with impulsive aggression in vastly confusing ways. One variant of the gene is associated with negative emotion, an attentional bias toward negative stimuli, anxiety, and depression risk when coupled with stressful risk factors. Its incidence is less than 50 percent worldwide but 70 to 80 percent in East Asian populations.

  * I once got to experience what this looks like for an extended stretch, as I traveled with a group of Somalis who were driving empty gasoline tankers back from Sudan to the Indian Ocean in Kenya for refilling. At the end of each day of driving through the desert, we’d sit around a campfire between the trucks, cooking a pot of spaghetti and camel’s milk. (Why that particular combo? That’s a whole other story. . . .) And inevitably one of the six Somalis would do something that was perceived as insulting by someone. There would be snarling, angry words, knives drawn from boots, two guys circling and lunging at each other until everyone else roused themselves to get the two to settle down. And then, the hospitality flip side of the culture on display, everyone would hurry over to make sure I got the best of the spaghetti/milk glob. “Eat, eat. You are our brother,” they’d say, including whichever two had just been slashing at each other.

  * Well, whether the feud actually ended in the 1890s is open to interpretation. While the families declared a truce and stopped the killings in 1891, their descendants battled for a week in 1979 on the game show Family Feud. The McCoys won three of the five games, while the Hatfields won more money.

  * What’s antisocial punishment about? The general interpretation is that people are being punished for being generous because they make everyone else look bad and increase the expectation of generosity from everyone else.

  * Ironic footnote: when coach passengers board through first class, the rate of air rage related to a sense of entitlement increases even more among the first-class passengers.

  * The paper generated an astonishing number of articles in the lay press whose titles were variants on “Stress and the City.”

  * The online world is now undergoing cultural evolution, wrestling with how to deal with the toxic behavior of some people online when they are shielded behind anonymity. Psychologists are even doing experiments, gifted with mammoth databases, to see how best to curb such behavior with top-down approaches (e.g., being banned by authorities) and interventions driven by peers (i.e., other players).

  * And there are remarkable similarities among such moralizing religions.

  * The authors used math straight out of chemistry for analyzing the extent of mixing between different types of solutions, plus some math from physics usually used to disentangle the contributions made by overlapping waves. I understood exactly zero of any of this and am putting faith in the vetting process of the journal, Science, the most selective science journal in the country.

  * I was in San Francisco for the quake, and much was made of the fact that fancy downtown hotels opened their doors to house people needing shelter. It’s worth noting that this generosity was for people made homeless by the quake, not people who were already homeless. For them the earthquake was just another day of scrabbling. The hotels supposedly required a credit card from people, not because they’d be charged for the room, but as evidence that this was the sort of person whose homelessness mattered. This well could have been apocryphal; it’s hard to imagine that the staff at reception needed to see someone’s plastic to tell the difference.

  * What were the “tightest” countries? Pakistan, Malaysia, India, Singapore, and South Korea. The least tight? Ukraine, Estonia, Hungary, Israel, and the Netherlands.

  * As a counter to this, though, people in the tropics also have to foresee annual fluctuations in weather, and no Swede has ever had to plan ahead for the monsoon season.

  * Pinker’s response to the cherry-picking charge is as follows: “Better Angels reports all the published estimates of per capita rates of violent death in the archaeological and anthropological literature I could find.” S. Pinker, “Violence: Clarified,” Sci 338 (2012): 327. If I understand what he is saying accurately, this feels a bit facile. To be facetious, this would be like not including Quakers in one’s analysis of violence because no one studying them had published something along the lines of “Estimated per-capita rates of death in Quaker communities due to gangland-style executions in nightclubs: zero; due to targeted drone missile strikes: zero; due to dirty bombs made with stolen plutonium: zero . . .”

  * When Chagnon was a guest lecturer in an anthro class of mine when I was an undergrad, students dressed up as Yanomamö in a salute to him (hell no, I didn’t—I’m too inhibited); apparently it was standard fare for anthro students to crash his road-trip lectures that way, which was probably totally irksome after a while, as he’d have to act all surprised and then pose for pictures with them. Chagnon was at the center of a firestorm of controversy in 2000 when the journalist Patrick Tierney, in his book Darkness in El Dorado: How Scientists and Journalists Devastated the Amazon, accused Chagnon and a collaborator of causing a genocidal measles epidemic among the Yanomamö, along with other ethical abuses of them as research subjects. The American Anthropological Association initially condemned Chagnon, which was generally interpreted as his being convicted as much for being an abrasive, anti–old boy enfant terrible as for the factuality of the charges. Eventually both the AAA and independent investigators exonerated Chagnon entirely, showing Tierney’s charges to range from the sloppy to the fraudulent. Chagnon’s most recent book, a memoir, is entitled Noble Savages: My Life Among Two Dangerous Tribes—the Yanomamö and the Anthropologists.

  * A distinction somehow reminiscent of Charlie the Tuna, back in those TV ads from my youth, being told that StarKist wants tuna that taste good, not tuna with good taste.

  * !Kung speak a click language, with the exclamation mark in their name the notation for the click sound. Informally known as “Bushmen,” they are part of the larger cultural group of Khoisan San found in Botswana, Namibia, Angola, and South Africa. As orientation, the movie The Gods Must Be Crazy featured the !Kung. Of note, while “!Kung” is the most familiar term most often used for these people, both they and most contemporary anthropologists use the term “Ju/’hoansi” instead.

  * I was raised in an anthropology department that was a major stronghold of !Kung fandom and generalized this to a huge fondness for all things African HG (probably in part because they’re all short). A tiny remnant HG tribe alternately called the Ndorobo or Okiek lives in forests north of the Serengeti in Kenya. They have an oddly symbiotic relationship with the neighboring Maasai, emerging from the forest to trade things or to serve a shamanistic role in some Maasai ceremony. They are short and silent, dressed in animal skins, and I’ve taken great pleasure in seeing how they unnerve tall, spear-toting Maasai. My Maasai friends would make fun of me for how obsessed I was with the Ndorobo.

  * Boehm emphasizes that anthropologists never really know what truly is going on among their research subjects until they’re privy to gossip. In doing my baboo
n research, I spent many seasons sharing camp with Maasai guys whom I knew relatively well and would hear about big goings-on in their community. Eventually, my soon-to-be wife started joining me in the field, and it was only then that we started to hear about the good stuff, via her becoming friends with some of the women—the usual of who was or wasn’t sleeping with whom.

  * We’ll soon see an exception to that, involving the nonreproducing individual helping relatives to reproduce.