Expert: John Shea - 1/14/2008

Question
I read somewhere that geneticists think it takes roughly a million years for a species  to fully adapt, in all ways(re teeth etc.) to a whole new diet(eg:- from a  fruitarian one to a diet high in meat). What's your take re this?

RPG

Answer
Dear Geoff
Rates of evolutionary change depend on so many variables that it is impossible to take an estimate like this at face value.  For example, the rate of morphological change in a fast-reproducing species (rodent, insects) will be faster than that for a slow-reproducing species (elephants, humans).  Population size also matters.  Evolutionary change can occur very rapidly among small isolated populations (e.g., finches on the Galapagos Islands), but rather slowly among populous species with broad distributions (again, humans).
It is also likely that some tissues are also more amenable to evolutionary change than others.
This is a short answer, but as I think you can see, it is a complex issue.
Cheers,
John Shea