In "The Selfish Gene" Dawkins makes the point that you do not need to have children to pass on your genes. You get 100% of your genes from your mother and fathe

In "The Selfish Gene" Dawkins makes the point that you do not need to have children to pass on your genes. You get 100% of your genes from your mother and father, and you full-brothers and full-sisters also get 100% of their genes from your mother and father. Therefore, from the point of view of your parents, there is absolutely no difference between you having a child yourself, or you bringing in enough extra food that your sister's child lives through the next famine (whereas they would have died without the food you brought in). In both cases, your parents end up with 1 extra grandchild, because of you. And this is a possible explanation for the fact that in humans the more sons a woman has, the more likely it is for the son to be homosexual. http://en.wikipedia.org/wiki/Fraternal_birth_order_and_male_sexual_orientation http://en.wikipedia.org/wiki/Fraternal_birth_order_and_male_... Biologists do not normally regard it is "altruism" if you give resources to someone who shares at least "50%" of your genes. (The 50% is in quotes because any 2 creatures that belong to the same species will have well over 99% of the same genes, and often 99.9% of the same genes. The "50%" actually refers to only to those genes that vary in your species. Dawkin talks about this, too, in "The Selfish Gene".)