The fact that humans have opposable thumbs is often used as a sure sign of our evolution.?
A single feature of a single species is not evidence of anything. It has to be a *shared* feature with a certain *group* of species. So if it was only humans that had opposable thumbs, then this would not be a sign of anything, much less a “sure sign”. But people who think that humans are the only species with opposable thumbs are just wrong. If anything the opposable thumb is more an explanation for why there is larger brain development in primates, compared other mammals. But it is *SEVERAL FACTS ALL CONSIDERED TOGETHER* that provide considerable evidence for relationships through common ancestry to other primates who also have opposable thumbs … and thus for evolution. Any one of them is just a piece of evidence … and may even have other explanations. But put them all *together* and no better explanation stands. What do *you* think all the following facts add up to? (1) All apes have opposable thumbs. (Chimps, bonobos, gorillas, orangutans, and the many species of gibbons.) This
