According to new research "an ancient ancestor of the elephant from 37 million years ago lived in water and had a similar lifestyle to a hippo"
There is further detail in analysis of the peer-reviewed research at Greg Laden's blog. And there is increasing evidence to support the claim - not just general observations about the hairless skin and long trunk being well suited for water, but specific and scientifically measurable features of the dental and renal systems have shown genuine evidence for the amphibious transition.
Elephants now live primarily on land, and the research talks about changes that happened tens of millions of years ago in Africa, it is a fair deduction that the region dried out considerably during that period. The modern human form also appeared tens of millions of years ago in Africa. You can see where I am going with this. Desmond Morris has been banging on for decades with the same suggestion.
Early humans may have evolved the ability to swim and lost the fur (unlike other chimpanzee groups) precisely because they lived in the water. The "aquatic ape" theory could be reborn.