Fortunately, progress is being made on disproving that last statement. Studies now prove that not just humans but such diverse animals as apes, dolphins, magpies, and elephants are self-aware. Not Exactly Rocket Science has a brief article on the subject.
I especially like one of the comments posted after the article, which says in part,
We sometimes fail to take into consideration the culture of the species when we administer "concrete" tests to prove or disprove ability in an animal or a bird. Animals and birds are far more sophisticated in their culture, communication and awareness than current methods of testing.Which ties in with the already-recognized problem of culturally-biased IQ tests for humans. (Here is an example of such a test, deliberately extreme to make the point.)
I always say that the physical differences between various species create differences in how intelligence is expressed. It requires a lot of paying attention to get around this barrier.