Columbia Professor Charged With Incest

[Mallardz]

Like Rob although I don't see why people would do it and think it's wrong I was completely unaware it was legal. People should be warned and by people I mean the residents of Norfolk.

[Warren Dew]

Well stated; I agree, with the proviso that the taboo may also involve some evolutionarily derived tendencies...

While I don't think they are a good guide to rational behavior, I do completely agree that there are evolutionary reasons for the incest taboo. I can even explain what they are.

First, as I believe someone pointed out earlier, it's not a "good of the species" argument. If people have recessive genetic defects, incest makes them more likely to result in a phenotypical defect immediately, but outbreeding simply keeps the genes for the defects around to cause the same problems later. Mathematically, the same percentage of the population will on average have the defective phenotype eventually; incest just makes them happen sooner, and outbreeding just puts the problem off.

If you look at it from the point of view of a given healthy gene in an individual that also has the defective gene, though, the situation is different. Incest makes it more likely that the healthy gene will end up in an individual with the defective phenotype in the very next generation. Outbreeding means the problem is put off for several generations, and during those generations, the healthy gene is more likely to end up in different descendants than the defective gene. That means that when the defective gene eventually contributes to a defective phenotype, it's likely to penalize some different healthy gene, not the healthy gene in the individual we were originally talking about - the individual deciding whether or not to participate in incest.

That means that any given healthy gene "wants" outbreeding, because that gives it a better chance to, essentially, "foist off" the consequences of any defective genes currently in the same body onto different healthy genes in future generations.

So yes, there's evolutionary pressure behind the incest taboo; however, it doesn't make for any logical reason to prohibit incest. In fact, a conscious, logical extension of the evolutionary argument would say that one wouldn't want to participate in incest oneself, but that one wouldn't care if other people did it. Evolutionary pressure doesn't work through logic, though, so people are left with an illogical emotional feeling of repugnance towards incest, which they then generalize to laws prohibiting incest without much conscious thought.