I don't think that is entirely right, since the history of human evolution is still very slippery to scientists. They have constructed our theoretical “evolution tree” with the fossils that have been found so far, and there are many “evolutionary leaps” or jumps in evolution with hundreds of thousands of years intervals since 2 million years ago and the farther you go in time, the more blurry our ancestor become, and the bigger the intervals between the evolution jumps. These evolutionary leaps are most likely caused by sudden changes in the genes of a given species. But in either case, all we have is theories as to why certain characteristics of the species changed; we know it was natural selection, but we speculate about environment and behavior. In any of these evolutionary “intervals” it is perfectly feasible that an ancestor that lived mainly in the sea shores lost the fur that is characteristic of apes; and developed many characteristics of aquatic mammals and then they went back to land. This could have perfectly happened in a “1 million year period”, so it gives much space for speculation. And this could have happened many times in our evolution, going back and forth from land to shore. So this could have also been a gradual change in our genetics. Around 5 million years ago, we share a common ancestor with today’s big apes and chimpanzees, and they haven’t lost their fur yet and don’t share the same semi-aquatic characteristics of the homo sapiens. About the picture of the monkeys: http://www.bloggerspoint.com/wp-content/uploads/2010/12/Monkeys-in-Japan-swim.jpg They started swimming in those hot springs since 1963; they found that this water protects them from cold, so now they go there every year. Normally monkeys are afraid of water, but under given circumstances they can adapt easily to a watery lifestyle. Also we have to consider that even in “climate change” periods when food supply was affected in land; there was still a lot of food in the shores.