What's the difference between a chimp and a human?

We are the Chimpanzees' closest relative in the animal kingdom, being even closer to them than gorillas are according to molecular data1. Only an estimated 1.4% of our DNA is different from theirs. Even gorillas are further from chimpanzees than we are. We are closer to chimpanzees than zebras are to horses, and yet just look at us...

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Clearly the ancestors of these two species became adapted to dramatically different niches since the the Pan/Homo split.
Chimps are hairy (just like all but one of the other 250+ types of primate.) Chimps are terrified of water and are very poor swimmers. Chimp babies are born very skinny with no excess fat to carry around with them.	Humans are naked (the only type of primate that is) With a little help babies learn to swim excellently and can grow up into superb skin-divers. Human babies are born comparatively fat making them much more buoyant in water than chimps.

Zoologists know that nakedness in mammals has evolved very few times and the number one cause of it happening appears to be through aquatic pressure.

The simplest explanation for our superior swimming & diving ability (compared to chimpanzees) is that since the Pan/Homo split, the ancestors of human beings lived in an environment where natural selection favoured that ability. 

Other explanations for this are comparatively complicated: The ability to swim, it is argued, is just another attribute of human intelligence. Infant fat is due to increased energy demands for our large growing brains. Nakedness has nothing to do with swimming abilities since many semi-aquatic mammals (e.g. otters, beavers, many types of seal) have retained their fur.

These arguments may, of course, be right. But it is curious why the most basic one: our ancestors evolved by water more than their's did - is not even considered as a possibility in the university-level text books on human evolution.

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Photo taken from the beautiful book "We are all Water Babies" Johnson & Odent (1995).