Our species is supposed to be similar to our hominid cousins the chimp, the gorilla and so on. But we possess several biological features which they strangely lack. The foremost of these are: We are largely hairless. And we have a layer of subcutaneous fat which is entirely absent in the other apes. Where did these modifications come from? The answer is provided by the other animals who also exclusively share these adaptations with us—the dolphin, the manatee, the hippopotamus and the seal, among others. The only reason to evolve this complex of features is for a mammal to become aquatic, spending a million years or so going from the land into the water.
The theory of an aquatic or semi-aquatic heritage for our species has a lot of explanatory power. Hair loses its insulating power in the water and becomes a liability for the swimmer or diver. A subcutaneous fat layer develops in place of hair for heat retention, and helps to fill in and streamline the body's hydrodynamics. The conscious breath control of the diving mammal is a first prerequisite for speech. Other features that we share with aquatic mammals include the glandular modifications which allow us to weep salty tears. And the infantile peachfuzz body hair we're all born with displays a hydrodynamic waterflow pattern. Upright walking easily phases in as a response to a lifetime of wading out to the deep. In other words, it looks like we learned to swim before we could walk.
Those biologists who are against the aquatic ape theory, and who have bothered to formulate a response to it, have their work cut out for them. And of course, there are alternate explanations for these physiological features which do not require an aquatic history. The problem with any such laundry list of explanations is that none of them connect the dots. Each anomaly is explained away with a separate explanation, and our precise similarity to the other aquatic mammals gets its own explanation as a coincidence. All this violates Occam's razor, the doctrine of simplicity which states, in essence, “A single explanation is better than multiple explanations.” A good hypothesis unites anomalies under one roof, instead of messily farming them out to separate explanations.
The theory that humankind descended from the trees and spread to the African savannah was developed in the 1800s from what little fossil evidence was available. These days the Savannah Hypothesis represents the entrenched orthodoxy in the study of humankind's origins, and like all established theories, does little to address the pesky new facts which have surfaced in the meantime. The old picture is that we dropped out of the trees and began roaming the grasslands. The new picture has a little million year swim party in the middle. We dropped out of the trees only to fill the marshes, swamps, estuaries, and tide pools, nurturing our big brains with the iodine in seafood. Only then, naked and dripping, did we heed the call of the dry land, and swim in to shore...
There's even a candidate for our aquatic ancestor. It seems there was a swamp-living ape that evolved on an island off of Italy back in the day. And of course islands are known for producing kind of way-out fauna. It seems this upright ape disappears in the fossil record right as Australopithecus strides onto the scene in the African veldt. Are they one and the same? Some researchers think so.
Terence McKenna adds another wrinkle to the story of our evolution, not by any support of the Aquatic Ape Hypothesis, but by adding psychedelic mushrooms to the mix. Did early human-apes discover these cow-patty delicacies when they started following the local wild cattle around? Looking for food, they found God, and a little linguistic stimulation... What's becoming obvious to us is that human prehistory was a lot more gonzo than you learned in school.
Recommended Reading: The Aquatic Ape Hypothesis by Elaine Morgan; The Archaic Revival by Terence McKenna
(Versions of this piece appear in the book Gonzo Science: Anomalies, Heresies, and Conspiracies , and on the Gonzo Science CD.)