Aquatic Ape | Zygoma

Recently I wrote about the Aquatic Ape Hypotheses, inspired by a conference being held on the subject.

Unsurprisingly, other people have also been busy discussing the topic and there has been a fun pseudoscientific parody called the “Space Ape Theory” which took off rather nicely on Twitter and is doing a good job of highlighting problems with the AAH.

Space Ape

This post will only be short, because other people have been dealing with this issue perfectly well without the need for my input, but I thought it might be useful to make visible the outcome of an extended conversation I had with AAH proponent Marcel F. Williams, in the comments section of my earlier post.

I decided to check some independent evidence about an inference made by Alister Hardy that led to the development of the AAH in the first place – the idea that having layers of subcutaneous fat was a trait unique to humans and aquatic mammals. This idea is still regularly cited by AAH proponents (especially Elaine Morgan) as a line of evidence for evolutionary convergence between humans and marine mammals due to the sharing of an aquatic habitat.

However, on checking the literature on primate husbandry it turns out that other primates have levels of subcutaneous fat that are directly comparable to humans if the animals have a ready supply of food, suggesting that humans are no different to other primates except in having a more stable food supply and leading a more sedentary life. This is supported by data from modern hunter-gatherer groups, who exhibit far lower fat levels than either farming or Western populations. Here’s a summary of the data with a link to the research:

Body fat – man vs monkey
Rhesus macaques in labs that are identified as being in the ‘optimal’ weight range have an average body fat content of 25% with individuals in the obese range averaging 42.7% [link opens pdf]

Autopsies of male orangutans show body fat levels range from 15% to 45% [link opens pdf]

Average body fat in Hadza hunter-gatherers averages 13.5% for men and 20% for women. In Western populations men average 22.5% and women average 37.9% [link opens pdf]

In short, humans are by no means unique in the primates with regard to their proportion of subcutaneous fat, so if any AAH proponent pulls out that old chestnut in conversation, be sure to put them right.