From Halopedia, the Halo wiki
Ow, I thought it was the other way around... :-$ I'll stop editing and turn everything back I can :-$
On Talk:Human, Jugus said that we should defer to canon with regard to the capitalization of "human". It is never capitalized in any canon source, so it should be written in lower case on Halopedia. He pointed out that "human" is not a proper noun, while the names of the other species are. He also stated that, since the creators of the series don't see fit to capitalize "human", neither should we.