Aquatic Ape – the body fat observation

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.

Oshine the morbidly obese Orangutan

Oshine the morbidly obese orangutan

Friday mystery object #191 answer

On Friday we had this skull submitted by Dr Ben Swift for identification:

mystery191amystery191c

Now this is quite obviously a primate, as it has a bony ring around the orbit, a bony back wall to the orbit and just eight incisors as opposed to the twelve that forms the basal condition for mammals. The teeth also tell us that this is an Old World Monkey (Cercopithecidae), since these primates only have eight premolars instead of the twelve you find in the New World Monkeys (Platyrrhini). The small canines suggest that this is the skull of a female.

From there it starts getting a bit more difficult. The fairly small size of the specimen ruled out a few genera, but the main features that helped narrow down the possibilities were the very flat face, the heavy bony rings around the orbits, the flaring of the zygomatic arches (cheekbones) and the short and rounded braincase. Effectively the only way to consider these features is to look at a lot of comparative specimens (the excellent Mammalian Crania Photographic Archive proved very useful for this).

After a lot of consideration I found myself in agreement with the suggestion of something from the genus  Continue reading

Friday mystery object #98 answer

On Friday I gave you this skull to identify:

Everyone spotted that it was from a monkey, perhaps unsurprisingly since monkeys have a very characteristic appearance, with a globular braincase and forward-facing eyes. The orbit is enclosed by a solid bony ring and there is a post-orbital wall made up of the sphenoid and ethmoid bones, that produces a cup-shaped eye socket.

But there are a lot of different monkey species – around 286 if you include the Apes (as you should). We can see that this specimen belongs to the Catarrhini clade (the Old World Monkeys and Apes) since it only has 2 premolars instead of the 3 premolars you’d expect in a New World Monkey (N.B. some extinct Catarrhines known from fossils have 3 premolars, so this useful distinction doesn’t actually help define the clade).

The size of the skull and the the shape of the nose region and the mandible isn’t quite right for an Ape, or a typical Cheek-pouch Monkey (like Macaques or Baboons), leaving us with the Colobinae (which includes Colobus Monkeys, Doucs, Langurs, Leaf Monkeys, Proboscis Monkeys, Snub-nosed Monkeys and Surelis).

Once we get this far it becomes rather more tricky to identify what species we’re dealing with (and it doesn’t help that the names are applied somewhat inconsistently), so I must offer congratulations to Jake, jonpaulkaiser, curatorialtrainee, henstridgesj, carlos grau and Steven D. Garber, PhD - all of whom suggested perfectly possible candidates amongst the Langurs and Snub-nosed Monkeys.

This skull is actually from a  Continue reading