[quote=@Double]
Humans are totally known in the Galaxy. I mean, what else could Recoome be? Or those orphan rebels that Gohan and Killin encountered on the way to Namek?
[/quote]

He's not human as far as we know. It's like in Star Wars or Star Trek. There are lots of humanoid races that might even look almost identical to humans, but they aren't. That's my assumption anyway.