Why humans differ from apes
Scientists find it easy to explain why we resemble the African apes so closely by pointing out that gorillas, chimpanzees and humans share a common ancestor.
It is much harder to explain why we differ from the gorilla and the chimpanzee much more markedly than they differ from one another. Something must have happened to cause one section of the ancestral ape population to proceed along an entirely different evolutionary path.
The most widely held theory, still taught in schools and universities, is that we are descended from apes which moved out of the forests onto the grasslands of the open savannah. The distinctly human features are thus supposed to be adaptations to a savannah environment.
In that case, we would expect to find at least some of these adaptations to be paralleled in other savannah mammals. But there is not a single instance of this, not even among species like baboons and vervets, which are descended from forest- dwelling ancestors.
This awkward fact has not caused savannah theorists to abandon their hypothesis, but it leaves a lot of problems unanswered. For example, on the question of why humans lost their body hair, it has been argued at various times that no explanation is called for, or that we may never know the reason, or even that there may not be a reason. These attitudes seem to be not merely defeatist, but fundamentally unscientific.
The Aquatic Ape Theory (AAT) offers an alternative scenario. It suggests that when our ancestors moved onto the savannah they were already different from the apes; that nakedness, bipedalism, and other modifications had begun to evolve much earlier, when the ape and human lines first diverged.
AAT points out that most of the "enigmatic" features of human physiology, though rare or even unique among land mammals, are common in aquatic ones. If we postulate that our earliest ancestors had found themselves living for a prolonged period in a flooded, semi-aquatic habitat, most of the unsolved problems become much easier to unravel.
There is powerful geological evidence to support this hypothesis, and nothing in the fossil record that is inconsistent with it. Some of the issues it raises are briefly outlined in the following pages.