Convergent evolution, or homoplasy, refers to the observation of widespread similarities between organisms that can’t be explained by common descent but instead calls for some other explanation. ENV’s Ann Gauger, Jonathan M. and Casey Luskin have all written on the subject, with Casey placing it on his list of the top 10 problems with Darwinian evolutionary theory. Our friend the physicist Lee Spetner, an MIT PhD and author of Not by Chance!: Shattering the Modern Theory of Evolution, offers this in-a-nutshell explanation of why homoplasy poses such a serious challenge to Darwinian theory:

The big problem for neo-Darwinian evolution is that they must show that the probability of getting the right mutations at the right time is large enough to make evolution work. We know the mutation rates (approximately) but we don’t know what fraction of them will be adaptive in any particular situation. It turns out that if we assume the fraction is large enough to make evolution work, then there are too many evolutionary pathways to allow convergent evolution.

Three cheers for brevity. That is very neatly put.