Why is This Debunked Evolutionary Theory so Persistent?

The AAH suggests our ancestors were once partially aquatic. (Source: Renato Bender)

About five million years ago, a shifting climate forced our ancestors to abandon their arboreal lifestyles, as African forests shifted into swathes of grasslands. Forced into migration, these ancestors evolved the upright bipedal posture we maintain today. This is called the Savannah Hypothesis, and remains the most popular theory to account for our bipedalism, but the consensus is not total. A controversial theory suggests that modern humans were not sculpted by the African savannah, but by the ocean; that our ancestors were once partially aquatic.

This theory is called the Aquatic Ape Hypothesis and suggests that bipedalism (along with many other human adaptations) can be accounted for by a period in our evolution when our ancestors lived an aquatic lifestyle. AAH has been controversial since its origin in 1960, largely ignored by most anthropologists but championed by a vocal minority. To be clear, AAH has been debunked as gaps in the fossil record have closed, but it is worth examining to pin down why some tenuous theories can hold the sway that they do, even when their evidence is faulty.

 A human and gorilla skeleton compared. The origin of bipedalism is at the center of AAH. (Source: Encyclopædia Britannica)

AAH holds its origins in a 1960 New Scientist article by marine biologist Alister Hardy, later championed by feminist Elain Morgan in 1982’s The Aquatic Ape, as it ran counter to the questionable,  patriarchy-tinged Naked Ape theory. Hardy and Morgan asserted that a dearth of fossils during the time period when modern humans diverged from apes could be explained from a single source—humans did not evolve their unique traits slowly, but all at once. Shifting sea levels required humans to become partially aquatic for a period of time—when the seas receded, we carried these traits with us.

Under the wide AAH umbrella hypothesis, nearly every last human adaptation can be explained by a time in our history when we lived in the water. Lack of body hair made swimming easier, more fat made us more buoyant, and wading eased us into bipedalism. Unfortunately for AAH’s champions, today’s more robust fossil record proves these traits evolved separately across a long period of time. Lack of body hair and higher fat levels allowed for greater thermoregulation on the savannah, while bipedalism may owe itself to lengthening of limbs needed for tree-climbing.

There are still plenty of questions to be had regarding human evolution—the Savannah Hypothesis is not universally accepted and there are different theories for our individual adaptations. The AAH case is useful as a reminder of the faultiness in seeking out one model to account for every last human adaptation. Perhaps that is why the theory remains popular, the idea of humans being a unique species created by a single unique circumstance can be more attractive than the chaotic randomness of evolution.