An excerpt from the book - The Moral Animal by Robert Wright.
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With Hamilton's theory in hand, it is 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 (the cow itself), which is now slaughtered, and may do nothing for the direct genetic legacy of its vehicle; dead cows cannot 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 worker ants have no direct legacy as most of them are sterile, but the genes responsible for this fact do just fine, thank you, so long as the time and energy 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 this thought.
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 promoting 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.
Naturally, the level of organism is of primary concern to human beings; human beings are organisms. But it is of secondary importance to natural selection. if there is sense in which natural selection "cares" about anything - and there is, metaphorically - that thing is not us; it is the information in our sex cells, our eggs, and our sperm. Of course, natural selection "wants" us to behave in certain ways. But, so long as we comply, it does not care whether we are made happy or sad in the process, whether we get physically mangled in our genes, even whether we die. The only thing natural selection ultimately "wants" to keep in good shape is the information in our genes, and it will countenance any suffering on our part that serves this purpose.
Hamiltonian math contains a potent symbol - r - which represents the degree of relatedness among organisms. Among full siblings, r is 1/2, among half siblings, nieces, nephews, aunts and uncles, it is 1/4, and among first cousins it is 1/8. The new math says that genes for sacrificial behavior will thrive so long as the cost to the altruist (in terms of impact on future reproductive success) is less than the benefit to the recipient (ditto) times the degrees of relatedness between the two.
When Hamilton introduced the theory of kin selection, he used as his example the very group of organisms that had perplexed Darwin. Like Darwin, he had been struck by the extraordinary self-sacrifice among many insects. He noted that, thanks to a bizarre form of reproduction, these species feature an unusually large r. Sister ants share 3/4 of their genes by common descent, not just 1/2. So altruism of extraordinary magnitude is justified in the eyes of natural selection.
So too with human beings - not groups of human beings, but the group of cells that make up a human being. At some point hundreds of millions of years ago, muticellular life arose. Societies of cells became so highly integrated as to qualify for the title "organism", and these organisms, eventually begat us. It is fair, technically speaking, to consider even so coherent an organism as a human being as tight-knit community of single-celled organisms. These cells exhibit a kind of cooperation and self-sacrifice that makes even the machine-like efficiency of an insect colony look ragged by comparison. Almost all the cells in the human body are sterile. Only the sex cells - our "queen bees" - get to make copies of themselves for posterity. That the zillions of sterile cells act as if they are perfectly content with this arrangement is doubtless grounded in the fact that the "r" between them and the sex cells is 1; genes in sterile cells are transmitted to future generations as assuredly via sperm of egg as they would be if their particular cellular vehicles were doing the transmitting. Again: when "r" is 1, altruism is ultimate.
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