The suggestion that our remote ancestors went through a semi-aquatic phase was first made as long ago as 1942, by a German scholar called Max Westenhöfer, but it did not attract any attention outside Germany. Alister Hardy, a young marine biologist, had thought of the same idea independently even earlier, in about 1930, although he did not make it public until 1960. Elaine Morganthen took it up and popularised it, with a feminist slant, in a series of books.
In The Scars of Evolution Morgan reviews the “orthodox” view of human evolution—that it took place on the savannah—and points out a number of difficulties with it, some of which she regards as fatal. The aquatic ape hypothesis, she claims, resolves most or all of these difficulties in a more satisfactory manner.
It is hardly surprising that, as an amateur without scientific credentials in this or any field, Morgan has encountered strong opposition from supporters of the conventional view. In her criticism of the savannah hypothesis of human origins she considers human hairlessness, fat amounts and distribution, bipedalism, the voluntary control of breathing (needed for speech), childbirth, and mating behaviour. All these, she believes, would be unsuitable for life on the savannah but would be much more suitable for an aquatic environment.
It is undoubtedly true that in these and other respects there are surprisingly large differences between ourselves and our nearest relatives, the chimpanzees and bonobos. It is also true that there are similarities between us and aquatic or semi-aquatic mammals such as hippopotamuses, seals, whales, beavers and others. These facts, Morgan claims, support her view that we went through an aquatic phase.
But critics have pointed out that the aquatic ape hypothesis has difficulties of its own. No aquatic mammals are truly bipedal. Many non-aquatic mammals do have at least some voluntary control of breathing. A more serious objection, I think, is that the presumed aquatic phase of the human ancestors would have been much shorter than that of other aquatic mammals yet it is supposed to have brought about very considerable modifications in anatomy and physiology. Would there have been time for these to occur?
There is certainly something attractive in the notion of an aquatic ape, and Morgan has done a good job here of presenting it in a popular form. Although she is a partisan of the theory she discusses the evidence fairly objectively. But I wish she had not repeated the old canard about us using only a small fraction of our brain potential (p.169).
I don’t think that the theory as presented here is really very plausible, but in a modified form it may have some validity. It has been suggested that Australopithecus robustus may have been a shellfish eater and that this may explain the powerful jaws that the species possessed. And it is likely that modern humans were beachcombers during part of the time that they were spreading round the world (see Out of Eden, by Stephen Oppenheimer). But all this is a long way away from the theory advanced by Morgan.