10 What Constitutes an Aquatic Mammal
Paul Leyhausen (8 pages)

SUMMARY

The Aquatic Ape hypothesis claims, among other things, to provide a better explanation of human near than my other proffered so far. Morgan (1972, l984), for instance has stated cursorily that during evolution all aquatic mammal tend co lose their pelt and become hairless.

About half of the mammalian orders have produced at least one aquatic or semi-aquatic species. The members of two orders have lost their terrestrial faculties completely and are unable to leave the water even temporarily: the Cetacea arid the Sirenia. These have indeed lost almost all their body hair. Of those mammalian  species which spend a great deal of hair time in the water but are not permanently bound to it, only the hippopotamuses and the Great Indian rhinoceros have lost almost all their hair. But the vast majority, front platypus and water-opossum to polar bear and elephant seal, have not only retained their pelt but have greatly improved it, with the result that many of them have been, and some still are, threatened with extinction because of their valuable fur. This includes even those who come to shore only for the business of reproduction but lead a pelagic life for the rest of the year.

But perhaps the pre-hominid ape who took to the water to escape predation by the leopard, as Morgan has graphically described had, like the extant anthropoid apes, already lost the soft underlayer of wool so essential to a protective fur. Did he, then, shed the coarse covering hair as well, since it was now useless? But mammals like the capybara, whose case is similar, did not.

Mammals who spend a considerable proportion of their life in the water even tropical water, have to safeguard themselves against losing body heat too rapidly. They are characterised by a shortening of the limbs and also of the tail where it is not used as a means of propulsion. The need for this safeguard is greater, the smaller the animal.

In short, a closer look at aquatic and semi-aquatic mammals does not support the Aquatic Ape hypothesis nor does this become any more plausible when we consider that, at the time when the epic flight from the impact of over-powerful terrestrial predators to the shores of the Indian Ocean is supposed to have taken place these same shores were still infested by Crocodylus pomsus and its likes.

1) Claims that as gibbons show some kinds of bipedalism arboreally, then the notion (and the assumption he thinks Hardy/Morgan have based their idea of wading origin for bipedality) that bipedalism arose out of ground dwelling apes is in danger.
2) Claims that "etchings of human forms on reindeer antlers seem to show that even as late as the "Aurignacian the body of Palaeolithic man was well covered with terminal hair." (p175) Goes onto to dispute Hardy's claim that the orientation of body hair (what little there is) follows the flow of water over a swimming body and that some hairs on the shoulder would actually create greater resistance.
3) Considers four groups of aquatic/semi-aquatic mammals.
i) Cetacea and Sirenia  stay in the water all the time. Are hairless and protected from heat loss by a thick layer of blubber. "Unfortunately they represent a way of life which even the most ardent aquatic partisan does not claim for that ape."
ii) Pinnipeds - are animals which spend most of their time in water. They have reduced their lims to short rudders but have not lost their pelts.
iii) Semi-aquatic mammals adapted to swimming and diving. With one exception (the hippopotamus), they are all well covered with hair. They have common adaptations for aquatic life, such as nostrils and ears which can be closed against the water, short limbs and webbed feet.
iv) Don't live in the water but take off to it readily to escape either from the heat of the day or from all too persistent parasitic insects. (e.g. Water buffalo and indian rhinoceros)  or predators (e.g. capybara, sitatunga and some deer.) To these life is a refuge but not a way of life. Often adapted to swamps. "It must be borne in mind that almost all mammals are able to swim well." p180

Class i) and ii) are clearly out of the question.

But even if the aquatic ape was in class iii) and iv) we still don't have any of their features - webbed feet, the ability to close our nostrils etc. - and almost none of those animals are naked. - a major contradiction.

He says "That human babies are natural swimmers and divers and that older children and adults can be trained to do even better is no argument."

"Alleged physiological adaptations" of humans - such as heart slow-down when diving does not stand up to scrutiny either. The reduced heartbeat of divers is not to be wondered at. The heartbeat slows down under any chest compression.

"The human skin is in no way adapted to being soaked in water for long periods, and has to be protected against osmotic pressure by covering it thickly with grease... or diver's suits.

Finally predation. Maybe leopards won't go in water but the predators that are already there are worse - crocodiles. "If I were a naked ape the size of a gibbon or slightly taller" he says "I should far prefer to face the leopard."

In short, available evidence shows...

1) Bipedal walk evolved in brachiators not waders of shallow water.

2) Early hominids - even early Homo sapiens were still fully covered with hair.

3) No aquatic or semi-aquatic mammal of about the same size of the hypothetical aquatic ape is naked.

Conclusion: There never was an aquatic ape.

1. Leyhausen's second assumption are is a little suspect. Perhaps Hardy and Morgan had assumed that nakedness had evolved before the hominid stage (> 2 mya) but I think this view is now discredited. Verhaegen and others would probably argue that hairlessness occurred more recently as a hominid trait.

2. The comparison with gibbons is also inappropriate. I am sure that Hardy and Morgan, as with most professional  paleoanthropologists, had assumed that bipedalism had evolved from ground dwelling apes. So this is hardly an argument against the AAH. Verhaegen's aquarboreal (and hence wading) model for early ape ancestors is actually more compatible with this idea than most orthodox views of bipedal origins - in that it allows a great deal of arboreality. The evidence that has emerged since the conference has shown increasingly arboreal (and wet) locations for the earliest bipeds.

3) Claim that early humans were hairy is surely a euro-centric view. Human nakedness is a universal trait and was almost certainly ancestral to early Homo if not before.

4) Mammalian criticisms are more difficult to answer. Generally, again, the view seems to expect Homo to have homologous traits with true aquatic mammals. Even the semi-aquatics he lists have lived in such niches far longer, generally, than the AAH claims for the ancestral aquatic ape. Remember - we are Hardy's original question was "Were we more aquatic in the past?" The real comparisons should be made with chimpanzees, bonobos and gorillas - we are certainly more aquatic than those species. The question he hasn't answered is... why?

5) He dismisses that human babies are natural swimmers without any reason.

6) Long term spells in water are not necessarily what our ancestors did. Infrequent but regular, short, fast swims and dives are more likely to have happened.

7) Predation. The point is our ancestors had both mediums of escape. The land to avoid crocs the water to avoid leopards. That must have given them an advantage.