Hamilton’s rule says that altruistic genes should increase in frequency when rB > C, when r is the identity-by-descent relatedness of the recipient to the actor, B is the fitness benefit to the recipient, and C is the fitness cost to the actor.
r is 0.5 [on average] for your parents, full siblings, and children. r is 0.25 for nieces and nephews.
All of this rests on certain assumptions: random mating, weak selection, linear payoffs, etc. But it’s useful.
Haldane put it into words: “Let us suppose that you carry a rare gene that affects your behavior so that you jump into a flooded river and save a child, but you have one chance
in ten of being drowned, while I do not possess the gene, and stand on the bank and watch the child drown. If the child’s your own child or your brother or sister, there is an even chance that this child will also have this gene, so five genes will be saved in children for one lost in an adult. If you save a grandchild or a nephew, the advantage is only two and a half to one. If you only save a first cousin, the effect is very slight. If you try to save your first cousin once removed the population is more likely to lose this valuable gene than to gain it. … It is clear that genes making for conduct of this kind would only have a
chance of spreading in rather small populations when most of the children were fairly near relatives of the man who risked his life.”
Ron Unz, in one of his occasional visits from Discworld, just offered a criticism of my ‘ gay germ’ theory of homosexuality. He suggests that people would surely develop resistance to any such germ – which general argument must explain why infectious diseases have never been a major problem for humans, right? Why malaria is no problem? The germs evolve too – that’s the point. Parasites can impose fitness burdens for millions of years.
He also says that I ‘viciously insulted’ the intelligence of his old prof E. O. Wilson. Ron does not know what true viciousness is. When E. O. Wilson supported a hypothesis that attempted to explained homosexuality by gay men helping close relatives in ways that produced more nieces and nephews, he sure sounded like an idiot. Because, looking at Hamilton’s rule, they’d have have to produce twice as many of those nieces/nephews to break even – a behavior twice as effective as mother love – which is impossible, of course, in any kind of Malthusian world. Moreover, they don’t even perform these helping behaviors. I am reminded of the time I attended a journal club at the University of New Mexico. They were discussing an article – In Our Genes – that Henry and I had written, so I had unusual insight into what the authors really meant. In the discussion, we (me, Kim Hill, a troop of grad students, and Keith Hunley being twitchy in the corner) were talking about how complex adaptations, in particular behaviors, developed slowly but could be lost rapidly if no longer favored by selection. This robs cave fish of their sight.
In particular, wolves have paternal care, but dogs don’t. Kim and I were discussed how to breed ‘ daddy dogs’ that would have such paternal care, which would inevitably lead to doggy marriage and big money for the Disney corporation, when one young lady in the troop suggest that maybe male dogs did help take care of the puppies, but had managed to keep everyone who ever lived from ever noticing it. Including Albert Payson Terhune and Jim Kjelgaard. Kim Hill, who knows all there is to know about Ache dogs, let alone the Ache themselves, said to her, in a tone of utter finality, “That does not happen.”
That young lady is a deep-dyed bred-in-the-bone idiot – but no more so than E. O. Wilson.
Ron Unz explains that his model took no more than five minutes to produce. I believe him.