[Physicist]

Two important points were left out of the article, however. First, there is the possibility that some of these genes only became disadvantages very recently. Milk consumption among adults, for example, was probably unheard-of until a few thousand years ago. Perhaps there simply hasn't been time to weed out a gene that only represents a minor survival disadvantage.

Second is statistics. A new allele that represents even a huge survival disadvantage (Hemophilia, for example) might gain a foothold in the genome--especially if it's recessive--simply by virtue of the fact that it didn't happen to kill its host. Alleles get weeded out when their hosts die or fail to breed, but if they themselves don't tip the balance, they have the same shot at survival as any other allele.

[diefree]

Re: lactose intolerance

I have a friend from Pula, just below Trieste who grew up on a farm there. She told me that they never drank milk, they drank water. The milk from the cows and goats was used to make cheese.

Also, my daughter went to school in France. She ate lunch at school and was never served milk, only water. Same goes for Italy, I believe.

[Karl_Lembke]

Second is statistics. A new allele that represents even a huge survival disadvantage (Hemophilia, for example) might gain a foothold in the genome--especially if it's recessive--simply by virtue of the fact that it didn't happen to kill its host. Alleles get weeded out when their hosts die or fail to breed, but if they themselves don't tip the balance, they have the same shot at survival as any other allele.

Indeed. I saw some computer simulations which showed that even alleles that lowered fitness by a pretty hefty amount still had a significant chance of becoming fixed in a population. The odds are higher for neutral mutations, and higher still for beneficial ones, otherwise we'd still be reproducing by fission and absorbing lunch through our membranes.