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Monday, August 03, 2009

Aquatic Humans, Gorillas, and Crocs

There are interesting arguments and evidence supporting the theory that an ancestor of homo sapiens had a semi-aquatic existence at one point, where they hung out in the water a lot, at least part of the time. If you haven't heard about this yet, here's the wikipedia entry, and here's a nice 17 minute TED video with Elaine Morgan.

One counter argument is that in Africa, where humanity evolved, semi-aquatic living would a have a risk of being attacked by aquatic animals such as crocodiles. I wondered what the distribution of gorillas and the distribution of crocodiles in Africa looked like. With a couple minutes of googling, I found two maps purporting to be the distribution of Gorillas in Africa (src), and the distribution of Crocodiles in Africa (src, the only one I could find). I coarsely scaled and overlapped them, and this is the result:

In this image, the crocodile distribution (grey) is widespread, and the Gorillas (red) appear to not share the same area as Crocs in the West, but they do in the East. There are two species of Eastern Gorilla, the Eastern Lowland Gorilla, and the Mountain Gorilla. The Mountain Gorilla lives nowhere near Crocs, and the Eastern Lowland Gorilla lives in lowland and mountain rainforests and subalpine forests.

The Western Gorillas do not generally seem to overlap with crocodiles and their habitat, and recently the Wildlife Conservation Society found more than 100,000 previously unreported gorillas have been living in the swamp forests of Lake Tele Community Reserve.

I don't know why I thought to look at gorillas first, as Chimpanzees are an even closer relative of humans, so I did the same thing with an image (src) of their distribution in Africa. The following is the same image as above, with the chimpanzee distribution in green:

As you can see, almost the entire distribution of Chimpanzees does not overlap with Crocodiles!

These images were taken from arbitrary sources on the internet, are coarsely scaled against each other, and I know nothing of their accuracies in distribution.

If these images are a coarse approximation of reality, it appears that the nearest neighbor species of Ape spends their time away from crocdiles. These maps in of themselves prove nothing, as these are maps of modern species and of questionable accuracy. However, if our human ancestors were living in similar regions as present day Apes, these maps suggest it is reasonable to suggest crocodiles weren't a problem for semi-aquatic ancestors of our genus, at least, not enough of one.

Burton MacKenZie