Reproduction

Back in the Old Testament, one of the best blessings that a man could receive from God was to have lots of descendants. God told Abraham that his descendants would be numerous as the stars in the sky.

This never made sense to me. Why should Abraham want descendants? I can see that Abraham might want some kids, maybe five or ten, to liven things up a bit or to take care of him in his old age, or just because he doesn't feel like exercising birth control. But descendants? Hoards of people multiplying and re-multiplying long after Abraham dies?

One way to rationalize Abraham's fondness for reproduction is to say that it was not an explicitly rational urge so much as it was a natural urge. Genes dictated to Abraham that he should reproduce, just as genes dictated that he should eat. Whatever Abraham's motives, much anecdotal evidence suggests that the urge-to-multiply gene is not universal: Many of my friends seem completely disinterested in having kids.

(It's not terribly surprising that the urge-to-multiply gene is not prominent, considering that for most of human history the urge-to-have-sex gene combined with a lack of birth control was sufficient to continue the human species. Now that we've got birth control, you can bet that the urge-to-reproduce gene will have much stronger role in future generations, as the reproductive lines of people who prefer birth control over children rapidly thin out.)

One of these non-reproductive friends of mine says that a reason for him being content without children is that his four siblings are reproducing at a high rate, and he counts each of his siblings children as equivalent to 0.5 children of his own.

According to a geneticist, you share with your siblings about half of the genes that distinguish your from the rest of humanity. Therefore, when your sibling has a child with an outsider, the genetic makeup of that kid is 0.25 of you. By contrast, when you have a kid of your own, the kid has half of your genes (granted, the situation could be completely different for you if you're a member of an exclusive religious sect or if you live in West Virginia). Since 0.25/0.5 = 0.5, it makes sense to count each child of a sibling as half your own.

The conclusion is obvious. I should pay my siblings to have more kids. It's funny, I already acted on this principle, long before I thought about it in these terms. I paid my brother an ipod for his first kid. In retrospect, this was a bad buy, since the kid apparently was already in the works before I dangled the ipod. I'll have to wait until he's sure he's done having kids before I start dangling cars and houses.

According to wikipedia, the urge to treat your siblings' children as your own could be hard-coded into our genes by evolution itself:

Under natural selection, a gene encoding a trait that enhances the fitness of each individual carrying it should increase in frequency within the population; and conversely, a gene that lowers the individual fitness of its carriers should be eliminated. However, a gene that prompts behavior which enhances the fitness of relatives but lowers that of the individual displaying the behavior, may nonetheless increase in frequency, because relatives often carry the same gene; this is the fundamental principle behind the theory of kin selection. According to the theory, the enhanced fitness of relatives can at times more than compensate for the fitness loss incurred by the individuals displaying the behavior.