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William D. Hamilton: In His Own Words

Frans Roes, a journalist based in the Netherlands, had the following conversation with William D. Hamilton in 1996.

by Frans Roes

William D. Hamilton
William D. Hamilton 

Frans Roes: Some of your ideas about how natural selection might favor a form of altruism were foreshadowed in the 1930s by Ronald Fisher's writings on the distastefulness of some insects. In what way?

W. D. Hamilton:  Fisher realized that if the insect is actually eaten by the predator in the course of the predator learning to avoid it, then whatever made that insect conspicuous to the predator is obviously disadvantageous to the individual being preyed on. So Fisher reasoned that the only way you could see that kind of selection getting started would be if the insects were gregarious, the group were siblings, and the predator, having tasted one and found it awful, were then to leave the rest of the group alone. The genes of the one eaten would then be indirectly promoted. Fisher also realized that this was not such a strong form of selection—not as strong as if it were the individual itself that had a form of protection. He made some remark about the selection going ahead at half the speed [since siblings share 50 percent of their genes], and that was one key early statement of the selection principle concerning the closeness of relatedness that I later came to develop.

Frans Roes: In part two of your 1964 article "The Genetical Evolution of Social Behaviour," you describe postreproductive behavior in two kinds of moths. What was the general phenomenon being illustrated?

W. D. Hamilton:  I noticed that someone had written about the postreproductive life spans of two kinds of moths. The author had noticed that the cryptic [well-camouflaged] insect tends to die very soon after it has laid its eggs, whereas the warningly colored ones [such as the distasteful monarch butterfly] often have a long life after they have laid their eggs. Again, this could be interpreted in terms of the kinship principle in a rather neat way. In the case of the cryptic one, if there are any relatives around in the neighborhood at all, it is advantageous for the moth to give up its life as soon as it has finished its own main business, laying its eggs. Because if it is around and the predator detects the moth and eats it, then that is a step in the predator's learning to detect other moths, perhaps including those that have not yet laid their eggs. So by causing itself to die soon after it has laid its eggs, it is actually doing a service to its cousins in the neighborhood. Quite the contrary holds for the warningly colored one. Once it has laid its eggs, it is in a position freely to use its warning colors to warn everyone it can. So it should continue to live and wait, and actually expose itself to being tasted by the predator, because that would be a step in teaching the predator to avoid its relatives.

Frans Roes:  In moths, both sexes have wings, but in some other insects either the males or the females are wingless. Why?

W. D. Hamilton:  Gene dispersal is a very crucial evolutionary phenomenon. For a female to sacrifice wings without having some other way of dispersal for her offspring would be a deadly mistake sooner or later. Where females have become wingless, there is some other way in which they or their offspring are dispersed to other localities. Most commonly they have a young stage, a larva, which is very mobile. Either it may climb onto other insects or onto a twig and from there be dispersed by wind. Often such larvae have long hairs that enable them to balloon on the wind very satisfactorily. In some species the wingless female is carried by the winged male—in his arms, almost literally. During this flight time he is mating with her, and finally he drops her off in a place suitable for egg laying. As for the males becoming wingless, if the male can inseminate a mobile female, then he doesn't have to worry about wings too much, because his genes can be carried off by the female. This often happens in cases where wingless males mate with their close relatives. So I think we can find some sort of rationale for many particular cases, but as far as I know, there is no very sweeping theory that explains why in some groups there is male winglessness and in others, female winglessness.

Frans Roes:  You went to Brazil in 1975 to study the fig wasp. What did you discover?

W. D. Hamilton:  Actually, I went to study life in rotting wood, but I ended up studying fig wasps instead. Each fig is a little world in itself. Some species of male fig wasps have no mouth and thus cannot eat; these are entirely fighting and mating machines—a very strange kind of animal with a very short life. In this incredible symbiotic pollination System, the males hatch out as adults from the fig's gauflowers, and the easiest—indeed the only—females to mate with are those hatching inside the same fig. Theory says that if the males mate with their sisters, and their sisters are capable of storing sperm, then you must expect the proportion of males to be cut down drastically. A mother should do much better if she produces a lot of females and just enough males to fertilize them. In that way she would get more descendants.

Frans Roes:  Why do the male insects of some species engage in fights to the death, while in other species the males tend to bluff?

W. D. Hamilton:  For fig wasps, there is not much point in bluffing inside the fig, because there is no time to "live and fight another day." Everything is over in a few hours, and if you don't fight now and try to win, then you won't be given another chance.

I saw bluffing with the giant Chilean stag beetle. In all the tournaments I held between males, it turned out to be the second-largest one that was the overall victor. This suggests that those with the biggest "tongs" were not actually as strong as they seemed to be. And they live in a situation where I can imagine that bluffing would pay off. Stag beetles are quite long-lived, and there are many flowers on the trees they could visit where females are arriving, and so it might be worthwhile to pretend that you are stronger than you are, in the hope that a rival male will go away. Then the bluff would have paid off.

Frans Roes:  You use a lot of mathematics in your work, and you write, "I had realized from experience that university people sometimes don't react well to common sense, and in any case, most of them listen to it harder if you first intimidate them with equations."

W. D. Hamilton:  Equations seem to frighten a lot of people; if you come at them with a display of mathematical strength, then they often back off. With me, you might call it a kind of bluff. If you have a simple idea, state it simply and forget about the mathematics. But often I use mathematics because I need to straighten out my own ideas. I have a somewhat illogical brain, and unless I put it through the mill of mathematics, I can continue to believe in the impossible for a long time.

Frans Roes: How much mathematics—and genetics—do you need to know to understand evolutionary theory?

W. D. Hamilton:  You do need to know the basics of genetics. I always found that good old standard Mendelism serves me quite well, and the modern ideas have not really changed the picture very much. I also think that in the mathematical field, you just have to know something about probability theory to understand how genes work in evolutionary processes.

Frans Roes:  A general question: Do living organisms behave as if they want to pass on their own genes, or do they behave as if each of their genes is trying to replicate itself, possibly at the expense of other genes of the same genome?

W. D. Hamilton:  This is a very deep and difficult question. One's impression is that there is a conflict between selfish genes, but largely it is being overridden by a kind of democracy that has arisen in the genome. [This will] suppress this intergene conflict, and the outcome is that the organism acts largely as a whole.

Frans Roes:  You write that evolutionary ideas "turn out to have, or are perceived to have, the unfortunate property of being solvents of a vital societal glue."

W. D. Hamilton: The glue that I am thinking of is various myths that tend to hold societies together. Religious people think that if people "believe" in evolution instead of, say, the gospels, they will no longer be able to celebrate simple honesty—or kindly and warm feelings toward others—as unequivocally "good." I think they exaggerate the danger, but they don't exaggerate a nothing. There is a danger of that kind.

Frans Roes:  How are evolutionists trying to deal with this problem?

W. D. Hamilton:  If you believe that we evolved out of animals—are animals—and have the same kinds of drives, it does not mean that we have to be selfish and inhumane. When you fully work out the consequences of the rules of kinship and of reciprocation, you will see that the outcome is in fact quite a moderate kind of behavior, that it avoids evil and is as good in holding the society together as are the religious myths. Indeed, under a rational theory, we should be able to do better for human happiness by avoiding various naive errors.

[ Frans Roes, "In His Own Words," June 2000, Natural History 109 (5):46-47.]

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