The Aquatic Ape Hypothesis

Today, I want to look at an interesting theory on human evolution that I’ve come across a couple times, known as The Aquatic Ape Hypothesis. This hypothesis isn’t really going to contribute much of anything to anything, whether it proves to be true or not. But nonetheless, I find competing theories of evolution to be fascinating. I most recently came across a mention of this theory in Survival of the Sickest. And then it was mentioned in a comment on my post What Was Our First Protein Source?

So what is this hypothesis? Well, it’s exactly what the name suggests, that humans are descended from apes that took to the water. Let’s first take a look at the arguments for the Aquatic Ape Hypothesis (AAH).(1)

The first argument for the Aquatic Ape idea comes from hairlessness. Getting rid of our thick primate hair makes it easier to swim and faster to dry off when exiting a body of water. The next argument comes from bipedalism. It is argued that the buoyant properties of water would have made the incremental evolution from quadrupedalism to bipedalism easier. Another argument comes from control over our breathing. We can deliberately control our breathing like many aquatic and semi-aquatic creatures, but unlike other land creatures.

There are many other anecdotal arguments for the Aquatic Ape hypothesis. A few are our fat surplus, perpendicular nostrils, the ability of infants to hold their breath and swim from birth, the greater nutrition of fish relative to land animals, and face-to-face sex, like in dolphins, are all cited as possible evidence for the influence of aquatic environments over our evolution.

Another piece of evidence in favor of the AAH is that “the extended infancy of humans could not have originally permitted survival as a land-based species”(2).

The first order of business in looking at the AAH is to not resort to ad hominem attacks on the people proposing the theory. We’ll just stick with straight facts.

First up, the ability of infants to swim:(3)

Babies, placed face down in the water, can hold their breath and rather inefficiently propel themselves through the water. Their motions are as much like crawling as they are like swimming. Babies cannot, however, lift their nostrils above water unassisted to breathe, which would seem to make their much-vaunted “swimming” ability worthless. Nor are human infants unique in being able to propel themselves through the water; the young of many, probably most, terrestrial mammal species can do the same.

How about the lack of fur/hair?(3)

Fur or hair is no great hindrance underwater. Fur seals, otters, beavers, and polar bears haven’t lost theirs and they swim better than we do. Only some aquatic mammals have lost all or most of their hair, and they are almost invariably very large species weighing a ton or more, whose ancestors have been living in the water for tens of millions of years. Contrary to popular thought, fur remains an effective insulator even in water, because it traps a layer of stagnant water (or in the case of the sea otter, air) next to the skin. …If anything, we lose heat too fast when we’re in the water (even tropical water), which should have made us retain our fur if we were really aquatic.

And subcutaneous fat?(3)

It is true that many aquatic animals have a thick layer of subcutaneous fat, but not, as Hardy supposed, for insulation. Their subcutaneous fat is mostly for streamlining and energy storage. Fat is a much poorer insulator than it is popularly thought to be, and poorer than fur even underwater. …Is the distribution of subcutaneous fat in humans somehow exceptional? Not at all. Sedentary zoo apes on a high-calorie diet accumulate subcutaneous fat stores in exactly the same places we do. What is exceptional is the difference between human and aquatic subcutaneous fat. Truly aquatic animals have thicker layers of fat surrounding the whole body. In humans, the fat layer is thinner and, on parts of the body, non-existent.

There’s also the fact that our close relatives, bonobos and orangutans, mate face-to-face. Oh, and many primates walk bipedally at times on land.

In the end, paleoanthropologists don’t give the AAH any credence because there’s truly no evidence in support of it. That’s enough for me to dismiss it with only a brief bit of research. I also found other nonsensical claims that the AAH supporters have come up with, but none of them hold water either (pun very much intended). Further, the claims seem to change every time one of them is disproved. The prevailing theory of evolution may well be wrong, but the AAH isn’t going to replace it. If you really want a more thorough and lengthy dissection, check out A Critical Analysis of the AAH.

Sources:
(1) What is the Aquatic Ape Hypothesis?
(2) Aquatic Ape Hypothesis - Wikipedia
(3) Did humans descend from “aquatic apes”?


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