Most mammals are covered with hair. The other hairless land mammals, like elephants & hippos, spend a considerable amount of time in the water. Plus, like us and unlike other primates, they have layers of subcutaneous fat. All of which suggests pre-humans spent a lot of time in and out of water at some point. I read about this idea in an old book called "The Descent of Woman" by Elaine Morgan.
Her idea is that pre-humans spent several million years living along the (perhaps African) sea shore, running into the water to escape large predators and generally adapting to ocean life. If that's all true it would help explain both our affection for the sea and its healthy effects on us.
