Why Your Mother Loves You

If you hope to get your obituary on the front page of the New York Times, I recommend spending a lifetime eloquently saying things of debatable importance. Witness Margaret Mead and Isaiah Berlin. Whatever you do, don't make a clear, major contribution to Western thought that has great philosophical ramifications. Witness William Hamilton, whose death was noted back on Page A18 of Friday's Times.

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You can't really blame the Times. Its news judgment here basically reflects the intellectual biases of its readers, which I guess is a reasonable thing for news judgment to do. And, as for the obituary itself: Though it did contain a couple of minor errors, it fairly well captured the view of Hamilton held by his colleagues—deep respect for a profoundly creative thinker. But his colleagues, being scientists, stuck to the facts and didn't rhapsodize about the philosophical import of his work. Hamilton is one of the few biologists—few scientists, in fact—for whom such rhapsodies would be in order.

Hamilton's signature accomplishment was the theory of kin selection. Kin selection—an idea that had been dimly perceived by past thinkers but had never been turned into a general and rigorous theory—is commonly said to explain the evolution of altruism among relatives. And it does. It explains why you feel more inclined to run into a burning building to save your sibling than to save just anybody.

The key insight here is that it is possible for a gene to fare well via natural selection even if the organism containing the gene doesn't fare well. An "altruism gene" (to oversimplify for expository purposes) can thrive by leading its organism to take risks, even risks that may lead to death, so long as the risks are taken on behalf of other organisms that stand a good chance of containing that gene. Which is to say: so long as the risks are taken on behalf of close kin. (Confused? Click here.)

The routinely cited examples of kin-selected altruism in animals—in ground squirrels that endanger themselves by emitting a warning call on seeing a predator, in insects that forgo reproduction, in people—are important. But equally important, and rarely mentioned, is that kin selection explains the existence of these animals; kin selection almost surely was crucial to the evolution of multicellular life to begin with.

After all, a multicelled organism (such as you) is in a sense a very tightly integrated society of cells, most of which seem quite altruistic: They labor without reproducing, a privilege left to the egg or sperm cells. But, through the lenses of Hamilton's theory, we can see that the altruism is superficial. The "sacrificial" labor of the nonreproductive cells actually serves the interests of their genes, because the reproductive cells contain the same genes. The genetic information of the sterile cells gets into the next generation just as surely as if they had sent it there themselves.

Various people who don't appreciate this application of kin selection have sat around pondering the mystery of the evolution of multicellular life. (This was for a time a common pastime among "complexity theorists" at the Santa Fe Institute, though I gather that some of them have since gotten more conversant in Darwinism.) And it's true that, even with kin selection, the threshold to complex multicellular life is a bit daunting; various tricky logistical feats have to get mastered. Still, with the theory of kin selection in hand, the origin of multicellular life is reduced from a mystery to a problem.

What's more, it becomes a problem that natural selection was likely to solve, given enough time. Since many single-celled forms of life reproduce clonally—no sex, no mixing up of genes—they often find themselves in the company of genetically identical neighbors. This is fertile ground for kin selection to work its magic—to instill an intercellular altruism that, via further kin selection, can grow until the hazy line between a cooperative society of cells and a single multicelled organism is crossed. And indeed, we now know that multicellular life evolved on several different occasions—five, maybe 10 times.

Kin selection is thus a key link in a broader argument that I've made repeatedly: The evolution of complex life—and of highly intelligent life—was likely from the beginning, given enough time. Hamilton was among the biologists who agree with me on this point, a fact I discovered while interviewing him for a documentary series that never came to fruition. Of course, he stressed, it wasn't foreordained that the intelligent species which finally evolved would be descended from an ape. "It might have been the descendant of a squirrel-like creature or a dolphin-like creature," he said. Still, the chance of some form of intelligent life evolving was so high that he was "quite favorably inclined to search for signs of intelligent life on other planets."

With minor prompting, Hamilton went off on flights of cosmic speculation. Given the likelihood of the evolution of intelligence, could natural selection have been set in motion with some end in mind? Yes, actually, he'd played around with sci-fi scenarios to that effect. Of course, the answer is unknowable, but "the theological possibility," he said, "is still certainly alive." So far as I know, Hamilton was not a religious man, which makes this sort of statement all the more a testament to his open-mindedness.

There is one other evolutionary likelihood that kin selection suggests: the invention of love. In a complexly sentient species (e.g., us), an altruistic disposition toward relatives tends to involve the feeling of love. And, though in our species feelings of love toward non-kin are possible, these were subsequent add-ons; love of kin preceded broader forms of love in evolutionary time. (Certainly maternal love goes way, way back, and maternal love—though a more intuitively obvious product of natural selection than love of a sibling—is technically just a special case of the general phenomenon of kin-selected altruism.) Given the power of the logic of kin selection—altruism has evolved repeatedly, independently—love would seem to have been fairly likely to show up eventually on a planet populated by lots of complex organisms.

Of course, the kind of love we "naturally" practice can be invidious and nasty. (Remember the Texas "Cheerleader Mom," who plotted to kill her daughter's rival for a cheerleading slot?) Still, the capacity to feel kindly toward people at all is the kernel of potential goodness that makes more benign forms of love possible. And, given the fact that hatred is a fairly obvious outgrowth of natural selection, it's nice to have this foundation on which goodness can potentially build.

Many of Hamilton's accomplishments were duly appreciated upon his death. The Times obituary noted his contribution to current thinking on how sexual reproduction evolved. And the obituary stressed that his theory of kin selection did much to inspire the "gene's eye view" of evolution that was central to E.O. Wilson's and Richard Dawkins' well-known writings on animal behavior. This fact alone—that Hamilton helped start a literal revolution in the understanding of animal behavior, including human behavior—would arguably be enough, in a just world, to get him front-page-obit treatment. When you throw in the things the obit missed, the case for better billing seems overwhelming. There is just something odd about seeing the man whose theory explains why multicellular life evolved, and why love was likely to come to this planet, on the same page with "Pee Wee King, 86, 'Tennessee Waltz' Writer" and "Daniel Yanofsky, 74, Canadian Chess Champion."

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