As organisms spread into new habitats, they diverge and differentiate to best adapt to their surroundings. But when separated species exploit similar niches, their body plans begin to converge, and they end up looking a lot like each other. Such is the case with Beaked Sea Snakes, uber-venomous consumers of spiny catfish and blowfish, long thought to be a single species but now shown by genetic analysis to be two. Meanwhile, PZ Myers considers the Creationist discipline of baraminology, which self-consciously strives to minimize the number of animals Noah needed to fit on his ark. Dr. Jean K. Lightner counts only 137 progenitors of modern mammals, meaning there has been an awful lot of evolution since the flood. Still, it's hard to explain a Beanie Baby in the wild without invoking Intelligent Design.
A cascade of events with unforeseen consequences is occurring around us. There are multiple causes. But overpopulation is the prime factor.