Last time, we looked at the Savanna Theory as an attempt to explain the transition that early human ancestors made from being forest dwellers to living on open ground. It does a pretty good job of it, but there are some rough patches. For instance, it spends a lot of time explaining how living out on the open grassland contributed to our bipedal gait, while new evidence shows we were upright walkers before we left the trees. Another problem is that it can’t account very well for our unique lack of hair, especially compared to other primates.
There is another theory that focuses on that period from the divergence of our line to the appearance of definite hominids in the fossil record. The Aquatic Ape Theory posits that our forebears spent a prolonged era in a wet, semi-aquatic environment, and that contributed to the evolution of a body plan that was very different from their relatives who stuck to the drier parts of the forest.
There are several things about us that are decidedly different from other mammals, most notably from other primates. Immediately obvious is our nakedness, or relative lack of hair. Not so obvious is our fatness, which is about ten times what it should be. Much of the fat is attached to the skin, while other land mammals tend to store their fat internally. Our bipedalism was retained and refined, even though other primates evolved quadrupedal gaits on the ground. We breathe differently from other land mammals. Unlike most other mammals, we have conscious control of our breathing. The other mammals with such control include seals and dolphins.
Here are some other differences. Humans sweat differently, from different glands in our skin, than do other mammals. Such excessive loss of water and salt doesn’t imply a dry environment, such as the savanna. We shed salty water from our eyes and noses, in addition to normal cleansing tears. We have millions of relatively large sebaceous glands that exude oil all over our heads and torsos. This is usually done to waterproof an animal’s fur or skin. Our brains have managed to grow unusually large. Other primates have larger brains than are found in most animals of their size, but they don’t approach the phenomenal growth rate of our brain.
These are some of the things the Aquatic Ape Theory has to explain. Let’s see how it does.
In 1930, while he was reading “Man’s Place among the Mammals,” by Frederic Wood Jones, Sir Alistair Hardy noticed a similarity between humans and aquatic mammals. They and we have a layer of fat attached to the skin which, in marine mammals, is called blubber. This led to the conjecture that there might have been a more aquatic phase in our evolution after our line and that of chimpanzees split from a common ancestor. Because this was outside his field, marine biology, and because he was shy of controversy so early in his career, Hardy didn’t make his ideas public for thirty years. When he did they were received first with controversy before being generally ignored.
The hypothesis got mentioned in Desmond Morris’ 1967 book, “The Naked Ape,” where it was seen by Elaine Morgan, who has been its most tireless advocate.
It still gets very little serious attention from paleoanthropologists and all of its claims have been criticized and found inadequate by its detractors. The aquatic theory still claims to be the only one that integrates and explains the many enigmas surrounding our differences from our primate relatives. We’ll look at some of them: our relative hairlessness, our fatness, bipedality, breathing, sweating and our large brains.
Of hundreds of primate species, only humans are hairless. Mammals become hairless in only two habitats: underground or around water. All the other mostly furless mammals that live above ground are either swimmers or wallowers, such as dolphins, manatees, hippos and tapirs. Even rhinos and elephants, which are drylanders now, had a more aquatic past and will wallow given the chance.
Humans are the fattest primates, having ten times the fat expected in an animal our size. Our fat is of the aquatic type rather than the hibernating type.
We are the only mammals that are primarily bipedal. Although there is evidence that brachiating apes developed bipedalism in the trees, the Aquatic Ape Theory says it was required for wading in the semi-aquatic habitat under the trees. Given the problems it still gives us millions of years later, such as back pain, hemorrhoids and hernias, bipedalism must have been necessary for some reason.
We are the only land mammals to have voluntary control of our breathing. Otherwise it is only found in aquatic mammals such as dolphins.
We sweat differently from other mammals, using different glands in the skin. We shed copious amounts of water and salt, okay in a semi-aquatic environment, wasteful on the dry savanna.
Finally, our brains are much bigger than chimps’. Why us and not them? Brain growth is better with abundant omega-3 fatty acids, which are concentrated in fish, shellfish and the eggs of seabirds. Without access to these fatty acids we might have been just another large ape.
What do you think? Does the Aquatic Ape Theory explain as much as the Savanna Theory?