The Aquatic Ape Theory (AAT)

Instructor: Stephanie Gorski

Steph has a PhD in Entomology and teaches college biology and ecology.

The Aquatic Ape Theory suggests that human ancestors spent much of their time in shoreline or aquatic environments. In this lesson, we'll discuss reasons this idea is compelling, as well as reasons it's not currently supported by the scientific community.

Blind Spots in Science

Scientists, at their core, are human. That isn't always a bad thing, but it means that sometimes the questions scientists choose to ask, or the places they choose to look for answers, are a result of their prejudices.

For example, Charles Darwin suggested that the earliest ancestors of humans probably lived in Africa. He was absolutely right, but racist attitudes of the time meant people were reluctant to look for our earliest ancestors there. Many people even fell for cheap pranks, such as the Piltdown man, a phony hominid fossil found in the United Kingdom. After decades of exhausting their search in Europe and the Americas, fossil-hunters chose Asia as the birthplace of humans. It was only in the late 1940s that scientists began accepting that humans evolved in Africa.

Man the Hunter?

If you've seen illustrations of 'the evolution of man,' you may have noticed that they almost always portray a man - specifically, a burly hunter. This is another prejudice based on early misunderstandings. There were some early ideas that humans developed bipedalism (the habit of walking on two feet), hairlessness, large brains, and other distinctly human features for hunting. The evidence simply has not panned out for this. But it's a compelling image for people who like to imagine their ancestors as early mammoth hunters. Besides physiological evidence and fossil evidence that this isn't accurate, these images forget fully half the population. What were women supposedly doing at that time?

What were the women doing all this time?
What were the women doing all this time?

Aquatic Apes

These cartoonish representations of macho 'cave men' were part of what attracted some feminists to the Aquatic Ape Theory, often abbreviated AAT, or the Aquatic Ape Hypothesis. But they were not the only reason.

Proponents of AAT suggest that our earliest ancestors lived around seashores and spent much of their time in shallow waters. Proponents of AAT suggest that many puzzling anatomical features of humans could be explained by the assumption that we evolved near the water.

For instance, bipedalism is difficult to understand because we're the only animals that have adopted it as a permanent lifestyle. You already know that bipedalism isn't an easy lifestyle, because you probably know quite a few people with back problems! The AAT suggests that bipedalism would be much easier to explain, and less punishing to the human body, if early humans spent a lot of time under water.

Humans also share several unusual features with aquatic mammals. Aquatic animals have extra fat cells and layers of fat that attach directly to the skin. So do humans, but most land mammals have much smaller fat deposits that are centered near the internal organs. Land mammals have thick coats of fur, unlike aquatic mammals - or humans. Humans also have unusual sweat gland physiology and waste a lot of water when they sweat, which would make sense if they lived in an environment where they did not have to conserve water.

Or Not?

The Aquatic Ape Theory interested marine biologist Alister Hardy since 1930, but he did not present it to the public until 1960. It was popularized by the author Elaine Morgan in the 1980s and 1990s. How has the idea developed since then? Not much at all.

Critics of AAT say that it does not read like a scientific proposal at all. Instead, it sounds like a really interesting story that is believed with religious fervor in its handful of adherents. In the decades since it was first suggested to the scientific community, the AAT has produced little in the way of fossil records, quantitative data, or any sort of hard evidence that would support it. It's telling that AAT's main proponent, Elaine Morgan, is a screenwriter rather than a trained scientist.

Critics also note that the weird examples cited by AAT have much more likely explanations. For instance, there is more evidence that humans evolved hairlessness to avoid parasites than that they evolved hairlessness for swimming. Fat distribution in humans, which AAT compares to fat distribution in aquatic animals, differs in important ways - shape, for instance, and how it is distributed over the lifetime of the organism. Fat distribution is more easily explained by sexual selection (some squishy parts look good) and by the sedentary lifestyle of many humans (monkeys get fat in captivity, too).

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