by D. Vogt

Created on: July 10, 2010

The aquatic ape hypothesis is a theory that, at some point in the past several million years ago, the ancestors of Homo sapiens lived on the seashore and spent enough time in the water that their bodies developed a number of adaptations to an aquatic lifestyle, which remain with us today and separate us from many other primates. No "aquatic ape" fossil specimens have ever been discovered, and at least for the moment, the theory is accepted only by a minority of anthropologists. However, it is important to note that a life in the water would intrinsically leave fewer fossil remains than a life on land, and that future discoveries could, as they have in the past, revolutionize our understanding of the evolution of the human race.

- Suggested Evidence for the Aquatic Ape Hypothesis -

There are several curious features of humans which might seem to indicate, at the very least, that we have spent a lot of time close to the marine environment in the past. Bipedalism, or the capacity to walk comfortably on two legs, is a skill that might have been easier to develop while wading in the ocean, where the water would provide greater support to the first clumsy walkers than they ever could benefit from on land. (It would also allow them to range farther out into the surf in search of food.) Humans also possess an involuntary physical response known as the mammalian diving reflex, which is mostly (though much more strongly) present in dolphins and seals.

In all cases of the mammalian diving reflex, when water is splashed on the animal's (or human's) face, the heartrate slows, the circulatory system begins to reduce its flow through the vulnerable and inefficient extremities, and, as we immerse in the water, a blood shift occurs which can reduce our vulnerability to increased water pressure well below the surface. This reflex only occurs when the water splashed is cold, and implies that we continue to maintain an automatic reflex from a point in our past where we actually needed these things in order to survive.

There are a few other features of human beings and human evolution which advocates suggest that the aquatic ape hypothesis could explain, as well. Babies are born with a layer of fat under the skin, known as subcutaneous fat, which is somewhat analogous to the thicker layer of "blubber" in cetaceans - and could suggest we once relied on similar insulation for long swims in the ocean. We also have very little body hair compared to our biological relatives.

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