Although questions like this are easily answerable, I feel very unsatisfied in answering them. There are several options.
Answering the actual question. Easy but lazy.
Answering a different question than the one asked, like "What are the vestigal organs". That question is interesting, but it's not what he asked.
Closing it as "Not a real question". Not so good, it is a real question.
Asking the poster to reformulate. This is likely to not make any difference, as the poster probably don't understand what he did wrong.
In one way I feel this site needs a whole new set of closing possibilities. A "Close as trivially answered", with suboptions like:
You can't prove a negative.
Actually in this case Wikipedia is a good source.