Comment on Open Thread, June 16-30, 2012

Sat, 23 Jun 2012 03:20:41 GMT

Forgive me, for my biology is a bit rusty.

A gene can become more common in a population without being selected for. However, invoking random genetic drift as an explanation is generally dirty pool, epistemically speaking. We should expect a gene that creates extra useless legs to be selected against. (Nutrients and energy spent maintaining the leg could be better used, the leg becomes more space for parasite invasion, etc.) Assuming that you were dealing with such cattle, you should assume that some humans were selecting for them. (No reason necessary. Humans totally do that sort of thing.)

I cannot think of any examples of a mutation causing extra limb development in vertebrates. However, certain parasites can totally cause extra limb development in amphibians. I doubt this is the case, but it is more likely than mutation.

Alternatively, consider there existing a selection effect on your observations. I wager that Indian cattle are less likely to be culled for having an extra leg that American cattle are. I'm just going off of stereotypes here, however.

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