I don’t think this is true. The smallest unit that evolution can operate on is a population. Individuals cannot evolve. So altruistic genes can and do arise in populations. Bacteria have genes for suidcide which get expressed when their is a strain on the colony’s resources. A honey bee hive has specialized its reproduction so that 99% of the colony is sterile. The genes that make worker bees sterile give the individual zero chance of reproducing, but it helps the hive as a whole. These genes were selected for by natural selection.
You will note that in these 2 examples (bacteria & Bees), are of species that pass on their genes in very diferent manner than humans. pure altruistic genes can be selected for in bacteria since all members of the colony have the same genes (from asexual reproduction). genetically speaking, helping your identical twin reproduce is as good as having the kids yourself. A similar situation exists in Bees (as well as ants and a few species of wasps IIRC), due to the specific way they have of passing genes ( i can’t remember all the details anymore) a drone bee is more closely related to its siblings than it would be to its own offspring. therefore, reproducing doesn’t make as much evolutionary sense as making sure the queen reproduces more. any evolutionary psych book will devote at least one chapter to the social insects if you want details.
in a species such as homo sapiens, you are most closely related to your own children (1/2 related to your children while 1/4 related to your siblings, and 1/8 related to your siblings children i believe) so similar behaviors are not selected for.
-luckie
Exactly half related to your parents or offspring, and on average half related to your full siblings. Remember, you and your sister share genes from both Mom and Dad.
this implies that i share 1/4 genes with her children. this high proportion of relatedness gives an advantage to helping both one’s siblings and their children. (the gay uncle effect, if you will.)
But I think the race-to-the-egg is not related to natural selection, since all of those little dudes carry the same set of genes. Unless the female had sexual intercourse with several males about the same time. In that case, faster could be selected for I guess, but it could also be selected against, according to the timing of the intercourse and ovulation.
The trouble with the “gay uncle” theory of kin selection is that an uncle is half as related their nieces and nephews as they would be to their own children.
Meaning that you get twice as much “bang for your buck” by contributing resources to your own children as you would to helping your brothers and sisters rear their children. If it was more advantageous to care for your nieces and nephews than your own kids everyone would do it. But mathematically it is not, so most people care for their own kids.
What this does mean is that a gene that causes homosexuality need not be nearly as deleterious as one might think. Homosexuals can and do have children, and even if they don’t kin selection might halve the fitness loss. But even if you put in as much effort as you would have put to your own kids, you still get only half the reward.
Now, I would also argue that our instincts for child-rearing are not quite so fine-tuned. It is easily possible for a human to care for a completely non-related child. We just have to look at how natural selection would treat making mistakes. One kind of mistake would be wasting resources taking care of a non-related child. Another kind of mistake would be rejecting your own child. The risk of rejecting your own child is much greater than the risk of accidentally accepting another child…and so we evolve to like babies in general. We like our particular babies even better, but we like all babies. And the process of recognizing “our” babies is social. We love “our” babies because we know them and recognize them. We don’t calculate their relatedness, because during human evolution any baby a human came in contact with was overwhelmingly likely to be closely related.