Behave: The Biology of Humans at Our Best and Worst

by Robert M. Sapolsky

  * That is, the heterozygotic state. I made the tough decision to bypass homozygosity and heterozygosity in the main text, in the interest of simplicity for the newcomer, and to instead exile the subject to footnotes. A brief primer: A point that I blithely ignored in the genetics chapter is that most species, including humans, are “diploid,” which means that there are actually two sets of chromosomes in each cell, with the same variety of genes. Eggs and sperm are specialized cells, being haploid (i.e., containing only a single copy of a chromosome). Put them together, and the egg that is destined to make you you is now fertilized (i.e., diploid). Thus you actually have two copies of each gene, one from each parent. (Footnote to a footnote: the exception is a specialized collection of genes in mitochondria, which come almost entirely from the mother). If both copies of the gene have sequences that code for identical copies of a protein, the gene is “homozygotic.” If there are two different versions, the gene is “heterozygotic.” What sort of trait is specified by the heterozygotic mixing of a gene? Some of the time, the result is a trait that is intermediate between the two possible forms of homozygosity. More often the heterozygotic form produces a trait that is identical to one of the two homozygotic forms. In other words, one of the versions “wins” out over the other and is called a “dominant” version of the gene. In contrast, versions of genes that produce a trait only when in the homozygotic form are “recessive.” If this is vastly confusing, I promise that you’ll be okay reading the rest of the book, nonetheless.

  * Poor Wynne-Edwards was actually a major figure in evolution and behavior but, thanks to shallow and superficial people, he is remembered only for having blown it with group selection. I, for example, haven’t a clue what else the guy ever did. His full name was Vero Copner Wynne-Edwards, which probably explains why he’s always called “V. C. Wynne-Edwards,” no doubt even as an infant.

  * The unique feature of the eusocial insect genetic system is that a sterile worker passes on more copies of her genes by helping the queen to reproduce than by reproducing herself. Meanwhile, the eusocial insect world has been shaken up by the fact that in some species (e.g., termites) there is a more conventional genetic system in place. People are still sorting that one out.

  * Note: No one is claiming that a langur monkey is thinking this through, any more than would be some brine shrimp who has evolved some sort of optimal behavioral reproductive strategy. An animal has the “goal” of “wanting” to pass on copies of their genes and thus “decides” to do X. This is just shorthand for saying something like “Over the course of millennia, individuals who do X have passed on copies of their genes at a higher rate, and this has become a common behavioral feature of this species.” Animals don’t know about evolutionary biology, just as prototypes of airplane wings in a wind tunnel don’t know about aerodynamics.

  * Or, more correctly, for each gene there’d be a 50 percent chance you’d share the same variant.

  * Also known as “inclusive fitness,” because a gene-based focus includes not only direct reproductive success (Darwinian fitness) but also payoffs derived from the success of other relatives, weighted by their degree of relatedness.

  * Note the term used—“invest”—reflecting a quasi-economic orientation to some of the analyses in this field.

  * Such fraternal polyandry occurs in resource-poor regions, basically acting as a means to decrease population growth and prevent family plots from winding up being below subsistance level when subdivided and inherited among all the sons in a family. Instead, all the brothers are married to the one woman, who has equal sexual access to all of them; the brothers “believe” that all of them, down to their infant brother, are equally biologically responsible for the children.

  * There is good evidence that inbreeding was responsible for the demise of the Spanish branch of the Habsburg dynasty. G. Alvarez et al., “The Role of Inbreeding in the Extinction of a European Royal Dynasty,” PLoS ONE 4 (2009): e5174.

  * Note: not all olfactory kin recognition is based on MHC proteins; there are numerous other sources of an individual olfactory signature. Note also how this can explain the kin-selection phenomenon mentioned earlier, where sperm form cooperative swimming aggregates only with sperm from the same individual or a close relative. How to pull this off? Use the MHC proteins on the surface of the sperm as Velcro—if two sperm have identical proteins (i.e., they’re from the same person), they aggregate very tightly; close relative, not as tightly but still pretty tightly; more distant relative, less tightly, etc.

  * Antisocial behavior in the name of kin selection reaches its apogee in the animal kingdom, as far as I’m concerned, with a phenomenon reported in a 2008 article in the Wall Street Journal. What restaurant/fast-food chain has the highest rate of fights among clientele, nationwide? Yup, you guessed it—Chuck E. Cheese’s, where the fighting is among parents on edge about anything that would detract from the perfection of their child’s birthday party. A particularly common scenario might be where a parent takes exception to some kid hogging a video game and forcefully intervenes to allow their own child to play, leading to an altercation between the parents—Cheney and Seyfarth’s monkeys would have no trouble following that one. As reported in another journalistic exposé, such incidents can also involve attacks on the Chuck E. Cheese’s mascot, including a case of a father accusing Chuck of having pinned his boy against a wall, while the mouse said he was just trying to squeeze by a crowd of overexcited kids: “The man ripped the mouse’s head off and yelled at him in front of said rowdy children, who probably were forever traumatized by the sight of the frightened 19-year-old kid’s head sticking out of the giant mouse’s neck.”

  * This one is a bit controversial, in that the bat colonies are often made up of somewhat related females, making way for a kin-selection argument.

  * To rein in the length of this chapter, I’ve had to force myself to relegate to this footnote a description of a system of reciprical altruism found in single-cell amoeba called Dictyostelium discoideum (aka slime mold). In order to reproduce, individual cells join in a structured colony in which about 80 percent of the cells reproduce and the rest play nonreproductive supporting roles. When the colony consists of two different genetic lines of amoebas, there is cooperation in that each line contributes about 20 percent of its cells to the unfun supporting role. Except that lines evolve to try to cheat by sneaking all their cells into the reproductive pool, and other lines evolve to detect cheaters and refuse to interact with them. For example, the amoebas express a cell-surface protein “adhesion molecule” that lets cells adhere to one another, forming the colony; an anticheater mechanism is to express an adhesion molecule that doesn’t recognize (i.e., attach to) the adhesion protein of a cheater line.

  * Some years ago a game show called Golden Balls ran in Britain. As the final step in a series of competitions, two competitors would face each other and play a modified version of the PD. There’d be a pot of money (potentially tens of thousands of pounds); each player would have to independently choose either “Split” or “Steal.” If both chose Split, they split the money. If one chose Split and the other Steal, the sucker got zero and the defector got everything. If they both chose Steal, they got nothing. YouTube is full of clips from various episodes, and they’re embarrassingly addictive. Also, see this Radiolab analysis of the show: www.youtube.com/watch?annotation_id=annotation_1155372699&feature=iv&src_vid=S0qjK3TWZE8&v=zUdBd7BDNu8.

  * The 1962 geopolitical thriller Fail-Safe, by Eugene Burdick and Harvey Wheeler, was premised on a Tit for Tat solution to a signal error. An electronic glitch causes an air force squadron of bombers with nuclear weapons to believe that the United States is under nuclear attack by the USSR; they are to destroy Moscow. The Americans and Soviets see what is happening, and the U.S. military unsuccessfully tries to get the planes to turn back; the Soviets assume the American “Oops, sorry” is a ruse and prepare an all-out counteratt
ack. The American president (modeled on JFK) tries to show his sincerity and stop the attack by sending up fighters to help Soviet jets shoot down the bomber squadron. A few are shot down, but a few get through, and most of the Soviet brass are still convinced it is a ruse. Finally, as the only means to prevent an all-out nuclear exchange, the president does a Tit for Tat, ordering a bomber to drop an equivalent bomb on New York City. Bummer of a signal error. This book scared the willies out of me when I was a kid. I’d regularly scan the skies over my hometown, New York, waiting to see the inevitable bomber.

  * I.e., “Oops, sorry, our bad taking out St. Petersburg. We thought we’d sorted out that bug after that Moscow snafu.”

  * A particularly clever exploitative strategy is called Pavlov. If you’re playing PD, the most advantageous outcomes for you, in rank order, are: (a) you defect while the other person is a sucker who cooperates; (b) you both cooperate; (c) you both defect; (d) you’re the sucker who cooperates while the other defects. Pavlov’s basic temperament is to cooperate, but every so often, randomly, it defects, and the rule is that, independent of those occasional random actions, if your play resulted in one of the two better outcomes, you do the same thing again next time; if the result was one of the two worse outcomes, you switch your behavior the next time. What that means is that if you are playing against Always Cooperate or a highly forgiving version of Forgiving Tit for Tat, your occasional random defections are either never or rarely punished, allowing you to exploit the other player at length.

  * This doesn’t begin to scratch the surface of the weirdness of the naked mole rat. They live underground, have giant incisors and no body hair so that they look like saber-toothed sausages, have remarkably little need for oxygen, have next to no pain receptors in their skin, live about ten times longer than other rodents (up to around thirty years), and are remarkably resistant to cancer. For this reason the prestigious science journal Nature named the naked mole rat its Vertebrate of the Year a few years ago, which is much cooler and more impressive than making People magazine’s list of the Fifty Most Beautiful People in the World.

  * The importance of founder populations was something championed by one of the giants of evolutionary biology, Ernst Mayr of Harvard; in his view, small founder populations were the driving force for new species forming; it is an extension of his thinking to view transient founder populations as a means to establish cooperation in a larger population. Remarkably, Mayr published four well-received books when he was over age ninety, the last one (What Makes Biology Unique?) in 2004 at age one hundred, shortly before his death. Inspirational guy, for a bunch of reasons.

  * Two technical notes. Social monogamy of pair-bonding species doesn’t always translate into sexual monogamy. “Tournament” is used by some solely to describe species in which the male-male competition literally takes the form of all the males gathering for competitive displays (as in sage grouse or some ungulate species) but is also used by many, as here, to more broadly describe multimale, multifemale promiscuous mating systems.

  * Goodall, in her chimp fieldwork, reported the case of Flint, the youngest child of the very aged Flo; she never fully weaned him, and he remained highly dependent on her, even into adolescence. When she died of old age, Flint underwent what can only be described as a reactive depression, failing to forage or socially interact; he died a month later.

  * What is an extreme version of such insulin resistance called by doctors? Gestational diabetes. In other words, we’re back to disciplinary buckets—if you’re an OB/GYN, we’re talking about a disease. If you’re an evolutionary biologist, we’re talking about a particularly tumultuous struggle between mom and fetus.

  * This arms race is revealed in two classes of diseases. Normal development represents a balancing of paternally derived progrowth genes and maternally derived ones doing the opposite. What if there is a mutation in a paternally derived imprinted gene, removing it from the equation? The counteracting maternal genes, unopposed, greatly inhibit fetal growth, and the fetus doesn’t implant. And what if the opposite occurs, with a mutation incapacitating the female gene, leaving the progrowth paternal genes working unopposed? Out-of-control growth of the placenta, resulting in an aggressive cancer, choriocarcinoma.

  * Neuroscientists often use the term “endophenotype,” which basically means “a trait that we used to be unable to detect at the phenotypic level but now can, thanks to some invention, so we’re going to call it an endophenotype, meaning a newly observable trait that is kind of inside you.” Your blood type is an endophenotype, detectable with an assay on a blood sample; the size of your amygdala is an endophenotype, detectable with a brain scanner.

  * By now it should be clear how often thinking about evolution is helped by metaphors and analogies. This prompted a great meta-analogy that everyone attributes to the biologist Steve Jones of University College London: “Evolution is to analogy as statues are to birdshit.”

  * Pääbo, who is a stunningly good scientist, pioneered the sequencing of ancient DNA, being the first to sequence the genomes of mammoths and Neanderthals.

  * A great analysis of this can be found in The Myth of Monogamy (New York: Henry Holt, 2002), by University of Washington psychologist David Barash and psychiatrist Judith Lipton.

  * I recently read in the Kenya Daily Nation about a case that takes one’s breath away, in its challenge not just to kin-selection thinking but to our notion of what boundaries of inhumanity would never be crossed. In parts of Tanzania there is the widespread belief that the organs of albinos have magical healing powers, and a shocking number of albino individuals are murdered there for that purpose. The story reports on a five-year-old albino girl in neighboring Kenya and the plot to smuggle her into Tanzania to sell her to a shaman to be sacrificed for her organs. The plotters? The girl’s stepfather and father.

  * For example, !Kung bushmen from the Kalahari in Botswana, aboriginal Australian groups, Mbuti Pygmies from the Congo, northern Canadian Inuits, and Amazonian populations.

  * Related to this was the notion that most of the evolution of behavior was not about dealing with the social complexities of fellow species members but about dealing with abiotic (i.e., nonbiological) pressures. In other words, that behavior evolved mostly for dealing with the environment, rather than for competing with other individuals. Again, the main implication of that for our purposes is that it would be another way in which the gradualist importance of interindividual competition was less than the sociobiologists thought. This emphasis on the importance of abiotic selective pressures was common among Soviet evolutionary biologists, probably reflecting not only the Marxist ideology but also the awful winters.

  * Who says a scientist can’t be the life of the party?

  * Something fascinating about the foxes and Moscow dogs: Both were selected primarily or exclusively for behavioral traits. But along with those traits came changes in appearance: The foxes are cute—shorter snouts, rounder ears and foreheads, curly tails, more varied coloration than standard foxes. And the Moscow dogs, exactly the opposite. If you want to domesticate a species, breed it for arrested development—a dog is basically a baby wolf, interacting with humans as if they’re all Mommy, and with the cute baby features. Same with the foxes, and just the opposite with the Moscow dogs. There is evidence that domestication mostly works on genes disproportionately related to brain development.

  * Apparently there has been a brouhaha over the fact that San Marco’s arches don’t quite fit the technical architectural definition of a spandrel. Whatever.

  * Considerable debate and speculation have gone into the question of whether female orgasm is a spandrel, carried along as baggage by the selection that gave rise to it in males. Enough said; fools rush in. . . .

  * Well, maybe not all that dramatically—someone poured a pitcher of water on his head. But still.

  * This easy picture was complicated by
Trivers being a friend and coauthor of Black Panther Party founder Huey Newton.

  * By great fortune, I arrived at Harvard as a freshman bio/anthropology major the season when Wilson published Sociobiology and all hell broke loose. And while it was fantastic, giddying fun for me, watching the fireworks, the personal nature of the attacks was clearly devastating to some of the principals—for example, protestors at Wilson’s talks regularly and absurdly chanted about his being a genocidal racist. Those years afforded me the chance to observe some of the players up close, to even get to know a few of them slightly, and both camps had roughly equal distributions of terrific, admirable role models and arrogant, insufferable egotists. My favorite story from this period: Many sociobiologists favored a macho, hard-edged persona. One day I rushed into the office of one of them, Professor X, holding a new paper I had just read. This guy was famed for a sociobiological model about some behavior, and this paper, by his adversary Professor Z, ripped apart the model with page after page of statistical analyses. “Wow, did you see this paper? Whaddya think?” I stupidly asked. Professor X flipped through the paper backward, glancing at the equations now and then. Finally he dismissively tossed the paper on his desk and delivered the ultimate sociobiological putdown: “Professor Z has a slide rule instead of a penis.”