The Moral Animal: Why We Are, the Way We Are: The New Science of Evolutionary Psychology (24 page)

Though Darwin finally conceived, at least vaguely, the correct explanation of insect sterility, and suspected that it might have relevance to human behavior, he came nowhere near seeing the breadth and diversity of the relevance. Neither did anyone else until a century later.

One reason for this may be that Darwin's explanation, as he phrased it, was hard to grasp. In
The Origin of Species
he wrote that the paradox of evolved sterility "is lessened, or, as I believe, disappears, when it is remembered that selection may be applied to the family, as well as to the individual, and may thus gain the desired end. Thus, a well-flavoured vegetable is cooked, and the individual is destroyed; but the horticulturist sows seeds of the same stock, and confidently expects to get nearly the same variety; breeders of cattle wish the flesh and fat to be well marbled together; the animal has been slaughtered, but the breeder goes with confidence to the same family."
⁴

However strange it may seem to bring plant and animal breeders into the picture, this made perfect sense after 1963, when a young British biologist named William D. Hamilton sketched out the theory of kin selection.
⁵
Hamilton's theory is an articulation and extension of Darwin's insight in the language of genetics, a language that didn't exist in Darwin's day.

The term kin selection itself suggests a link with Darwin's assertion
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that "selection may be applied to the family," and not just to the individual organism. But this suggestion, while true, is misleading. The beauty of Hamilton's theory is that it sees selection as taking place not so much at the level of the individual
or
the family, but, in an important sense, at the level of the gene. Hamilton was the first to clearly sound this central theme of the new Darwinian paradigm: looking at survival from the gene's point of view.

Consider a young ground squirrel that has not yet produced any offspring and that, upon sighting a predator, gets up on its hind legs and delivers a loud alarm call, which may attract the predator's attention and bring sudden death. If you look at natural selection the way almost all biologists looked at it through the mid-twentieth century — a process concerned with the survival and reproduction of animals, and of their offspring — this warning call doesn't make sense. If the ground squirrel giving it has no offspring to save, then the warning call is evolutionary suicide. Right? This is the question that was momentously answered in the negative by Hamilton.

In the Hamiltonian view, attention shifts from the ground squirrel that is sounding the alarm to the gene (or, in real life, the series of genes) responsible for the alarm. After all, ground squirrels don't live forever, and neither do any other animals. The only potentially immortal organic entity is a gene (or, strictly speaking, the pattern of information encoded in the gene, since the physical gene itself will pass away after conveying the pattern through replication). So, in an evolutionary time frame, over hundreds or thousands or millions of generations, the question isn't how individual animals fare; we all know the finally grim answer to that one. The question is how individual genes fare. Some will pass away and some will thrive, and which do which is a matter of consequence. How will a "suicidal warning call" gene fare?

The somewhat surprising answer, which lay at the core of Hamilton's theory, is: quite well, under the right circumstances. The reason is that the ground squirrel containing the gene may have some nearby relatives who will be saved by the alarm call, and some of those relatives probably carry the same gene. Half of all brothers and sisters, for example, can be assumed to possess the gene (unless they're half-siblings, in which case the fraction is a still nontrivial one-fourth).
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If the warning call saves the lives of four full siblings that would otherwise die, two of which carry the gene responsible for it, then the gene has done well for itself, even if the sentry containing it pays the ultimate sacrifice. This superficially selfless gene will do much better over the ages than a superficially selfish gene that induced its carrier to scurry to safety while four siblings — and two copies of the gene, on average — perished.
^*
The same is true if the gene saves only one full sibling, while giving the sentry a one-in-four chance of dying. Over the long run, there will be two genes saved for every gene lost.

There is nothing mystical going on here. Genes don't magically sense the presence of copies of themselves in other organisms and try to save them. Genes aren't clairvoyant, or even conscious; they don't "try" to do anything. But should a gene appear that
happens
to make its vehicle behave in ways that help the survival or reproductive prospects of other vehicles likely to contain a copy of that gene, then the gene may thrive, even if prospects for
its
vehicle are lowered in the process. This is kin selection.

This logic could apply, as in this case, to a gene that inclines a mammal to produce a warning call when it sees a threat to its home burrow, where relatives reside. The logic could also apply to a gene that leads an insect to be sterile, so long as the insect spends its life helping fertile relatives (who contain the gene in "unexpressed" form) to survive or reproduce. And the logic could apply to genes inclining human beings to sense early on who their siblings are and thereafter share food with them, give guidance to them, defend them, and so on — genes, in other words, leading to sympathy, empathy, compassion: genes for love.

A failure to appreciate familial love had helped keep the principle of kin selection from clear view before Hamilton's day. In 1955, in
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a popular article, the British biologist J.B.S. Haldane had noted that a gene inclining you to jump in a river and save a drowning child, taking a one-in-ten chance of dying, could flourish so long as the child were your offspring or your brother or sister; the gene could even spread, at a slower rate, if that child were your first cousin, since first cousins share, on average, one eighth of your genes. But rather than sustain this train of thought, he cut it short by observing that in emergencies people don't have time to make mathematical calculations; and surely, he said, our Paleolithic ancestors hadn't run around calculating their degree of relatedness to each other. So Haldane concluded that genes for heroism would spread only "in rather small populations where most of the children were fairly near relatives of the man who risked his life."
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In other words: an indiscriminate heroism, reflecting the average degree of relatedness to people in the general vicinity, could evolve if that average were fairly high.

For all Haldane's insight in looking at things from the gene's, rather than the individual's, point of view, his failure to follow this logic to its end is odd, to say the least. It's as if he thought natural selection realizes its calculations by having organisms consciously repeat them, rather than by filling organisms with feelings that, in their fine contours, are proxies for calculation. Hadn't Haldane noticed that people tend to have the warmest feelings for the people who share the largest fraction of their genes? And that people are more inclined to risk their lives for the people they feel warmly toward? Why should it matter that Paleolithic men weren't math whizzes? They were animals; they had feelings.

Technically speaking, Haldane was right insofar as he went. Within a small, closely related population, an indiscriminate altruism could indeed evolve. And that's true even though some of the altruism would get spent on people who weren't relatives. After all, even if you channel your altruism precisely toward siblings, some of it is wasted, in evolutionary terms, since siblings don't share all your genes, and any given sibling may not carry the gene responsible for the altruism. What matters, in both cases, is that the altruism gene
tends
to improve prospects for vehicles that will
tend
to carry copies of itself; what matters is that the gene does more good than harm, in the long run, to its own proliferation. Behavior always takes place
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amid uncertainty, and all natural selection can do is play the odds. In the Haldane scenario the way to play the odds is to instill a mild and generalized altruism, the exact strength depending on the average extent of kinship with people regularly in the vicinity. This is conceivable.

But as Hamilton noted in 1964, natural selection will, given the opportunity, improve the odds by minimizing uncertainty. Any genes that sharpen the precision with which altruism is channeled will thrive. A gene that leads a chimpanzee to give two ounces of meat to a sibling will eventually prevail over a gene that leads it to give an ounce to a sibling and an ounce to an unrelated chimp. So unless identifying kin is very hard, evolution should produce a strong and well-targeted strain of benevolence, not a weak and diffuse strain. And that is what has happened. It has happened, at least to some extent, with ground squirrels, which are more likely to deliver warning calls in the presence of close kin.
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It has happened, to some extent, with chimpanzees and other nonhuman primates, which often have uniquely supportive sibling relationships. And it has happened, to a great extent, with us.

Maybe the world would be a better place if it hadn't. Brotherly love in the literal sense comes at the expense of brotherly love in the biblical sense; the more precisely we bestow unconditional kindness on relatives, the less of it is left over for others. (This, some believe, is what kept Haldane, a Marxist, from facing the truth.) But, for better or worse, the literal kind of brotherly love is the kind we have.

Many social insects recognize their kin with the help of chemical signals called pheromones. It is less clear how humans and other mammals figure out (consciously or unconsciously) who their kin are. Surely seeing our mother feed and care for a child day after day is one conspicuous cue. We may also, by observing our mother's social affiliations, develop a sense for, say, who her sister is, and hence who her sister's offspring are. Besides, since the advent of language, mothers have been able to tell us who's who — instruction it is in their genetic interest to give and in our genetic interest to heed. (That is to say, genes inclining the mother to help children identify kin would thrive, as would genes inclining children to pay attention.) It's hard to say what other kin-recognition mechanisms, if any, are
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at work, since experiments that might settle the question involve unethical things like removing children from families.
⁸

What's clear is that mechanisms exist. Anyone with siblings — anyone in any culture — is familiar with the empathy for a sibling in great need, the sense of fulfillment at giving aid, the guilt at not giving it. Anyone who has endured a sibling's death is familiar with grief. These people know what love is, and they have kin selection to thank for it.

That goes double for males, who, in the absence of kin selection, might never have felt deep love at all. Back before our species became high in male parental investment, there was no reason for males to be intensely altruistic toward offspring. That sort of affection was the exclusive province of females, in part because only they could be sure who their offspring were. But males could be pretty sure who their brothers and sisters were, so love crept into their psyches via kin selection. Had males not thus acquired the capacity for sibling love, they might not have been so readily steered toward high male parental investment, and the even deeper love it brings. Evolution can only work with the raw materials that happen to be lying around; if love for certain kinds of children — siblings — hadn't been part of males' minds several million years ago, the path to loving their own children — the path to high MPI — might have been too tortuous.

With Hamilton's theory in hand, it's easier to appreciate the connection Darwin saw between a cow that has "well marbled" beef, and gets slaughtered and eaten, and an ant that works hard all its life without issue. The cow gene responsible for the good marbling, to be sure, has done nothing for its vehicle, which is now slaughtered, and may do nothing for the direct genetic legacy of its vehicle; dead cows can't have more offspring. But the gene will still do much for the indirect genetic legacy of its vehicle, for by producing the marbling, it prompts a farmer to feed and breed the vehicle's close relatives, some of which contain copies of the gene. So too with the sterile ant. The ant has no direct legacy, but the genes responsible for this fact do just fine, thank you, so long as the time and energy
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that would have been devoted to reproduction are profitably spent helping close relatives be prolific. Though the gene for sterility lies dormant in these relatives, it is there, and passes to the next generation, where it again produces gobs of sterile altruists devoted to its transmission. This is the exact sense in which worker bees and tasty cattle are alike: some genes, by impeding their transmission through one conduit, lubricate their transmission through others, and the net result is more transmission.

That Darwin, working with no knowledge of genes, with no sound understanding of the nature of heredity, should sense this parallel a century before Hamilton is one of the higher tributes to the care and precision of his thought.

Still, let there be no doubt about the superiority of Hamilton's version of kin selection to Darwin's. It is accurate enough to say, as Darwin did, that sometimes (as with insect sterility) natural selection operates on the family and sometimes on the individual organism. But why not keep things simple? Why not just say that in both of these cases, the ultimate unit of selection is the gene? Why not make a single brief statement that encompasses all forms of natural selection? Namely: those genes that are conducive to the survival and reproduction of copies of themselves are the genes that win. They may do this straightforwardly, by prompting their vehicle to survive, beget offspring, and equip the offspring for survival and reproduction. Or they may do this circuitously — by, say, prompting their vehicle to labor tirelessly, sterilely, and "selflessly," so that a queen ant can have lots of offspring containing them. However the genes get the job done, it is selfish from their point of view, even if it seems altruistic at the level of the organism. Hence the title of Richard Dawkins's book,
The Selfish Gene
. (The title has caught flack from people who note that genes don't have intentions, and so can't be "selfish." True, of course, but the phrase wasn't meant literally.)