glyco-man

All cells in almost all living organisms are covered with a coat of carbohydrates, serving a variety of functions ranging from recognition of 'self' to complex cell-cell signaling. Some of these carbohydrates belong to a family of sugars known as sialic acids.

Somewhere along the course of human evolution, while we were still 'great apes', one gene got deleted. Not spectacular, as evolutionary changes go. What it means is that our cells have only one type of sialic acid while chimps have two (which differ by a single oxygen atom).

So?

It appears that this is possibly the sole reason that we contract malaria (the Plasmodium falciparum one) and avian flu but orangutans don't. The reason humans suffer excruciating day-long contractions to give birth and chimps finish it off and leave for lunch in half an hour. The reason eating red meat might increase the incidence of cancer. Stunningly (though highly speculative), this may even be part of the reason our brains are what they are. (We have unique brain-specific sialic acid-binding protein expression patterns, one of the major chemical differences between ape and human brains)

All this because of one less oxygen atom.

If this sounds cool (or you don't believe me), check out Ajit Varki and his gang, the guys who've done it all. And the real dirt starts here: Nature 446:1023-1029.