The Price of Altruism (43 page)
Read The Price of Altruism Online
Authors: Oren Harman
Still, alongside kin selection, reciprocity and the games it engenders have been valuable spectacles through which to gaze at Nature and her ways. There is a downside, however, for what all three scaling ropes share in common is a rather dubious conquest: Whether a monkey scratches it’s neighbor’s back, or a bee fatally loses its entrails when it stings an invader at the hive, altruism à la Hamilton, Trivers, and von Neumann is never what it seems. In fact, when it comes to altruism, the gene’s-eye view of evolution leads to positively uninspiring places. “The economy of nature is competitive from beginning to end,” the biologist Michael Ghiselin wrote,
…the impulses that lead one animal to sacrifice himself for another turn out to have their ultimate rationale in gaining advantage over a third…. Where it is in his own interest, every organism may reasonably be expected to aid his fellows…. Yet given a full chance to act in his own interest, nothing but expediency will restrain him from brutalizing, from maiming, from murdering—his brother, his mate, his parent, or his child. Scratch an “altruist” and watch a “hypocrite” bleed.
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The gene’s-eye view can lead to strange places, too. “Consider a pride of lions gnawing at a kill,” Dawkins asks us to imagine.
An individual who eats less than her physiological requirement is, in effect behaving altruistically towards others who get more as a result. If these others were close kin, such restraint might be favored by kin selection. But the kind of mutation that could lead to such altruistic restraint could be ludicrously simple. A genetic propensity to bad teeth might slow down the rate at which an individual could chew at the meat. The gene for bad teeth would be, in the full sense of the technical term, a gene for altruism, and it might indeed be favored by kin selection.
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“Tooth decay as altruism?” biologist and philosopher Helena Cronin asked, amazed, in her 1991 book
The Ant and the Peacock
. “That’s hardly how saintly self-sacrifice was originally envisaged.” And yet, she added, “The logic is unassailable.”
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After years of debate, it seemed, the genes, evolution’s real scions, had finally provided the answer: Natural goodness was slowly being unmasked.
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Until group selection started making a comeback.
For both Williams and for Dawkins, the gene as replicator offered a strong argument against evolution working at the level of the group; if genes were the only permanent unit in nature, how could the eye of selection peruse anything else? As a bookkeeping device, scoring genes in populations helped keep good track of evolutionary change. But “selfish genes” were not fashioned merely as a metaphor: The point of view they engendered negated evolution at any other level.
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And yet, when reconsidered by theorists beginning in the eighties, chief among them David Sloan Wilson, it began to become clear that the unit of selection and the level of selection depended on entirely different criteria. Of course genes were replicators, and clear units of permanence. But whether a certain level of life could be viewed by selection depended not on
permanence
but on
where fitness differences resided in the biological hierarchy
. Here is why: If a population is viewed as a nested hierarchy of units, with genes existing within individuals, individuals existing within groups, groups existing within populations and so on, fitness differences can exist at any or all levels of the hierarchy because
heritable variation
can exist at all these levels. The gene’s-eye point of view therefore says nothing about the possibility of group selection; genes, after all, can evolve by outcompeting other genes within an individual, or—via the traits they confer—by helping individuals outcompete other individuals within a group, or by helping one group outcompete another. Even if the genes are the replicators, it still needs to be determined whether they evolve by between-gene/individual selection, between-individual/group selection, or between-group/population selection. Despite all the history and hype, the gene’s-eye view and group selection are not, and never should have been, antithetical.
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When it comes to altruism this multilevel selection approach is all the more important. For as Darwin himself perceived when contemplating the ants, altruism, like any other trait, is sure to have evolved. What makes altruism special is that it reduces individual fitness within the group while benefiting the group as a whole. The only real question, then, is whether between-group differences in fitness are ever strong enough for within-group altruism to evolve.
This is an empirical question. And it is why, after thinking it over following their first cryptic telephone conversation, Hamilton wrote to George that he was enchanted with his formula. The covariance equation, he suddenly saw, had elegantly wiped away years of confusion. Over his own head, and the heads of Haldane, Fisher, Wright, and Allee, of Emerson and Kropotkin and Huxley, it had returned to Darwin’s own original insight: Evolution can occur at different levels simultaneously. The beauty of it was that this simple mathematical tautology could now help define where selection was acting most strongly for each and every trait.
Hamilton thought that he was the only person in the world who understood just how momentous George’s formulation really was. For what covariance allowed to see was that while the different ropes scaling Mount Modern-Evolutionary-Biology seemed as though they had been thrown from the crest of an entirely different peak, in fact their climbers were simply making ascents up different faces of the very same mountain. Inclusive fitness made it seem as though “altruism” was always just apparent since by sacrificing himself an “altruist” might die, but his genes live on in the bodies of kin. Reciprocal altruism, on the other hand, also took the sting out of altruism, but the price in this case was always repaid to the very one who had made the sacrifice. Finally, variations on the prisoner’s dilemma fashioned reciprocation a game, often making this ascent, too, seem as though it were progressing up a distinct slope.
The trick, of course, was to be able to see how each ascent related to the other, how scaling up one face could illuminate something about the mountain without having to exclude the lessons learned from alternative climbs. Inclusive fitness, for example, taught that genetic relatedness was important for the evolution of altruism. This
was
important. But what a multilevel frigate could do, armed with the ammunition of a covariance gunner, was to put it in perspective. Here are Sloan Wilson and the philosopher Elliott Sober:
For all its insights, kin selection theory has played the role of a powerful spotlight that rivets our attention to genetic relatedness. In the center of the spotlight stand identical twins, who are expected to be totally altruistic toward each other. The light fades as genetic relatedness declines, with unrelated individuals standing in the darkness. How can a group of unrelated individuals behave as an adaptive unit when the members have no genetic interest in one another?
Replacing kin selection theory with multilevel selection theory is like shutting off the spotlight and illuminating the entire stage. Genealogical relatedness is suddenly seen as only one of many factors that can influence the fundamental ingredients of natural selection—phenotypic variation, heritability, and fitness consequences. The random assortment of genes into individuals provides all the raw material that is needed to evolve individual-level adaptations; the random assortment of individuals into groups provides similar raw material for group-level adaptations. Mechanisms of nonrandom assortment exist that can allow strong altruism to evolve among nonrelatives. Nothing could be clearer from the standpoint of multilevel selection theory, and nothing could be more obscure from the standpoint of kin selection theory.
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If in a gene’s-eye view individuals are “vehicles,” the genes within the body saddled together as if on the very same boat, then a multilevel approach showing that groups are vehicles, too, can be translated into a gene’s-eye view model.
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Everything depends on whether the right conditions render individuals in a group akin to genes within a body, if “mechanisms of nonrandom assortment,” in other words, do in fact really exist. Relatedness can be one such mechanism, but it needn’t be the only one. Goodness depends on association, not necessarily family.
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It took him some time, but Hamilton began to grasp this after the cryptic phone conversation with George (“I thought you’d see that,” George told him when he finally came around). Suddenly Maynard Smith’s 1964
Nature
article attacking Wynne-Edwards, the one that had made Hamilton so mad, didn’t look so unequivocal: Sharply distinguishing between kin selection and group selection, after all, no longer seemed always to the point.
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Hamilton made this clear in a paper he wrote in 1975 showing how the evolution of altruism between relatives is just an instance of group selection rather than an alternative explanation for an “apparent” altruism. It was the first application of George’s full covariance equation to an evolutionary problem.
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Not only kin selection but games of reciprocation, too, could now be viewed from an entirely new angle. If two hamadryas baboons grooming each other are playing a kind of prisoner’s dilemma they can easily be defined as a group. Clearly if one is an altruist and the other a free rider, the free rider will always win a benefit without paying any cost, and the altruist will always pay a cost without winning any benefit: Within the “group” it pays to be selfish. But what happens if the pair is compared with a second “group” made up of two altruistic baboons that groom each other loyally? Now, suddenly, selfishness becomes an impediment, for group B will be cleaner on average than group A, and therefore healthier and more likely to sire more off spring. The question then becomes whether between-individual/within-group forces are as strong as between-group/within-population ones. If association between the baboons is random, then they will be, and selfishness will beat out altruism. But if association is not random—if altruists, say, can choose to unite and stick together, leaving selfish types to pair vacuously with one another—altruistic genes enhancing grooming behavior will be able to evolve.
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Amazingly, Hamilton’s paper fell on deaf ears. Even though George had succeeded in changing his mind about group selection, and even though, starting in the late seventies, Hamilton began to be referred to by many as the greatest Darwinian since Darwin and to win every possible accolade, group selection remained under the shadow of the gene’s-eye point of view. If group selection exists in theory, most people said, it is too weak a force to play a role in nature. Into the eighties and nineties, and into the twenty-first century, theorists like Sloan Wilson continued to speak, frustrated, to those who would not listen.
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Slowly this is beginning to change.
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In 1981 Hamilton’s female-biased sex-ratio paper was exposed for what it really was—an instance of the test George Williams had asked for, showing group selection at work.
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A further oft-cited example, which Lewontin caught on to very early, involves the virulence of pathogens: If evolution acts on each single pathogen within a host, a “race” will begin between the pathogen and the host’s immune system, and the more hypervirulent the individual viruses the greater the chance they will all perish together with the host. On the other hand, if selection works on the entire virus population, attenuating it somewhat, there is a greater chance that the host will come into contact with other potential hosts (since not incapacitated or dead), and therefore a greater chance for the virus population to move on and survive. Just such an example was occurring in Australia: A virus,
Myxoma
, was introduced in the late sixties by its department of agriculture to help subdue a rabbit population wreaking havoc and growing dangerously out of control. At first the virus was devastating, but soon it began to attenuate. Lewontin explained:
When rabbits from the wild were tested against laboratory strains of virus, it was found that the rabbits had become resistant, as would be expected from simple individual selection. However, when virus recovered from the wild was tested against laboratory rabbits, it was discovered that the virus had become less virulent, which cannot be explained by individual selection.
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In fact group selection even emerged as a clinical concept, since hospital procedures and public health practices can be employed to favor the evolution of low-virulence strains. This became known as “Darwinian medicine,” and George Williams himself emerged as a pioneer late in his career.
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Slowly but surely further examples began to surface.
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And while group selection remains hotly contested, and good experimental examples are still few and far between, there’s no arguing that it’s making a comeback, at the very least in theory.
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Today even the entomologist Edward O. Wilson, whose 1975 book
Sociobiology
was a central pillar of the gene’s-eye-view approach, has come to believe that selection works at different levels. “Superorganisms” like bee and ant communities are literally giant vehicles, and the altruism they foster, Allee and Emerson would have been glad to know, is in that sense genuine and real.
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