[Ragnar54]

This theory suggests that evolution requires stress. That would not seem to explain the Birds of Paradise. The only stress the males would feel would be due to rejection, and the rejected ones would not get to breed.

Perhaps a better explanation of the sudden appearance of changes is that we will never have more than a statistically small sample of fossils from any given era. We might not see an evolutionary change until an environmental change has given it an advantage and the "mutant" population explodes.

[PatrickHenry]

This theory suggests that evolution requires stress. That would not seem to explain the Birds of Paradise. The only stress the males would feel would be due to rejection, and the rejected ones would not get to breed.

Environmental stress isn't the only factor in natural selection. Sexual selection is well-recognized. Environmental stress is one of the causes of mutation, but not the only cause.