Humans and apes share a common ancestor, yet Homo sapiens have several traits that distinguish them from orangutans, chimpanzees, bonobos, and the rest. We are exclusively bipedal, lack fur, and have more fat.
One attempt to explain these differences is the aquatic ape hypothesis, an idea first proposed by physician Max Westenhöfer and marine biologist Alister Hardy in the 1920s and 1930s. They argued that a branch of apes was forced from the trees and began hunting for food on the shores. The notion is not that man came directly from the sea a la Creature from the Black Lagoon. Rather, following the split with chimpanzees, the Homo genus went through a stage of being aquatic or at least amphibian, and this branch became us. In the hypothesis, wading, swimming, and diving for food had a large evolutionary impact on how we turned out.
While humans and apes have very similar appearance, the most obvious difference is our lack of fur, save for a couple of guys I’ve seen in the locker room. There are only a few other mammals without fur, and this includes dolphins, manatees, and whales, all of whom have smooth, oily skin that allows for more efficient swimming. However, this is the result of being adapted for swimming over tens of millions of years. Also, other savanna mammals such as elephants, hippos, and rhinos are without fur, while seals, otters, and beavers maintained theirs. Therefore, it does not necessarily follow that an aquatic ape would have lost its coat.
Which leads us to the second point of the aquatic ape hypothesis. Instead of fur, humans have subcutaneous body fat, which apes have little of, and dolphins and whales have plenty of. This fat would seem to be disadvantageous for a hunter-gatherer but beneficial for a creature needing buoyancy and insulation from cold water.
However, apes have the same type of subcutaneous fat as people, they just have less of it. Moreover, human fat is distinct from the blubber of furless sea mammals, and would not help an aquatic creature stay afloat or keep warm.
A third claim centers on our bipedalism. In water, this makes it possible to wade to a greater depth, and when swimming, enables a coordinated motion of arm strokes and leg kicks. Supporters of the hypothesis point out that while biologists feel bipedalism emerged for life on the savannah, no other animals from there developed the trait.
However, bipedalism has developed only in land animals and is not an adaptation for an aquatic life. Also, animals who spend all or part of their time in the water are either four-legged creatures like the hippopotamus or specialized swimmers without legs, like dolphins.
Another point made to support the aquatic ape hypothesis is that humans can control their breathing consciously, a trait they share with mammals who have the ability to dive. However, most primates can hold their breath, as can dogs. Humans have much better breath control than other animals, but they also use their breath for speech and other skills not possessed by other creatures. Therefore, an aquatic ape would not need humans’ specialized breath control.
The hypothesis runs counter to the archeological and anthropological evidence that hominids developed on Rift Valley savannas. This evidence further suggests a major divergence between the great apes and hominids about six million years ago. Also, fossils from around 4.4 million years ago reveal terrestrial bipedal hominids with small brains and fur, which would be inconsistent with the hypothesis.
Animal Planet ran a faux documentary on mermaids in 2012, then aired an equally silly sequel the following year. The subject matter was presented in advertisements as genuine and the only hint to the contrary came during the closing credits, when a disclaimer in minuscule print flashed on the screen so briefly it could have been mistaken for a subliminal message.
While the shows were staged, they introduced the notion that mermaids could be explained through the aquatic ape hypothesis. This idea has since received positive mention on the Discovery Channel and the History Channel. While the notion is presented as possibly shedding new light on human evolution, the fact that formerly erudite networks are promoting mermaids seems more an example of us having devolved.