Stupidity. Sorry if this sounds rude, but it's very true. It's one of the first things I think about when I think of what human means.
Usually one might say something like 'conscious thought' o the 'ability to talk and communicate with others of the same species'... yeah, tu could say that, but our stupidity trumps all that, doesn't it? We have conscious thought and the ability to speak and yet we still fail at using either.
Modern humans (Homo sapiens, primarily ssp. Homo sapiens sapiens) are the only extant members of Hominina clade (or human clade), a branch of the taxonomical tribe Hominini belonging to the family of great apes. They are characterized por erect posture and bipedal locomotion; manual dexterity and increased tool use, compared to other animals; and a general trend toward larger, más complex brains and societies.