Clownfish, the aquarium pet of choice since the release of Disney's "Finding Nemo", live in such a rigid social structure in the wild that if one of the dominant breeding adults is removed, the size, status and even sex of the other clownfish change rapidly to return the group to the status quo.

"If the female of the group dies, the male changes sex and becomes the breeding female," said Cornell University evolutionary biologist Peter Buston, "while the largest non-breeder becomes the breeding male."

So, if these fish can change in real-time, surely it's plausible for humans to evolve within the timeframe of two generations?