True, CK, but the unfortunate Makoko is only one example of many (if perhaps the most famous one). I have also seen cited a case where no fewer than four chimpanzees drowned at a single facility in moats or small pools over a relatively brief period of time. ALL the technical and popular literature I have checked (and at this stage it’s a lot) is absolutely universal in the opinion that swimming ability in all the apes is at best minimal. Most state unequivocally that apes (gorilla, chimpanzee, orangutan, and gibbons; many monkeys, including some that are informally called “apes” can swim well) do not swim. The more cautious authors will say “appear to be unable to swim,” while some will venture the opinion that “perhaps young ones could be trained to swim,” although the experiment seems to have been made often and I have never seen a citation of a success.
The only specific citations for swimming apes I have seen so far have been (1) the four chimps dog-paddling across a stream in Equatorial Guinea I mentioned in a previous post, but considered as doubtful by Reynolds; and (2) a pet orangutan that was lured aboard a steamer in an attempt to “kidnap” it from its owner. When the steamer pulled away from the dock, the ape jumped overboad and managed to make it to shore. Ever afterward he would flee to the jungle whenever a steamer was in town. But he seems to have been the veritable Johnny Weismuller of anthropoids. (Please do not ask me the name of the orangutan. I can probably find out, but I don’t have the time right now.) And as you say a single example does not make a case.
This is quite mysterious, as I said, because apes are anatomically so similar to humans. Occasionally someone will speculate about a physical cause, such as the “center of gravity (OK, mass)” argument, or that apes may have low body fat. But while the “center of gravity” argument could conceivably apply to an adult male gorilla, in which the heavily-muscled shoulders could force the muzzle under, I don’t see how it could apply to a young chimp. The body-fat argument is slightly more plausible, as it is often mentioned that a drowning ape “sank like a stone.” However, many captives, at least gorillas, are obese and should be able to float. I have seen no general data on body-fat percentages to back this contention, and I think people are just grasping at straws.
What seems to be the case is that apes are simply psychologically averse to water, at least deep water, and when they fall in or are placed in it they just go bonkers and thrash around helplessly until they drown (or sometimes don’t even struggle). This happens even if they are only a few feet from shore. There are few healthy adult humans, even non-swimmers, that would not be able to rescue themselves in such circumstances, but apes very often don’t. There are any number of anecdotes in the literature of owners placing a gibbon, orang, or whatever (usually young, but sometimes adult) in the water as an experiment and then having to rescue it when it became distressed and started to go under.
Some young gorillas will play in a basin of water, but others seem to be afraid of it. On the other hand, virtually all human babies will play happily in a pool. And apes in nature seem to be averse to crossing even shallow water; in “The Mountain Gorilla” George Schaller mentions that they will usually cross even small streams on fallen logs to avoid wading.
Distribution also argues that apes rarely if ever cross water. The range of the Eastern Lowland Gorilla is circumscribed by the Niger and the Congo (Zaire), while the Western Lowland Gorilla is found a great distance away at the headwaters of some of the Congo tributaries. The ranges of the eastern and western subspecies of Common Chimpanzee is likewise split by the Niger, and Common Chimps are not found south of the Congo. The Pygmy Chimp (Bonobo), usually considered a difererent species, on the other hand, is restricted to the south side of the Congo. While Orangs occur on the larger islands of Indonesia, they seem to have been isolated there by rising sea levels after the Pleistocene. And the ranges of some gibbons seem to be limited by major rivers in Southeast Asia.
So there you have it. There seems to be a mountain of evidence, both anecdotal and experimental, that if apes swim at all, it is only under the most extraordinary circumstances. They have rarely if ever been observed to swim in nature; in captivity they often drown in pools of water only a few feet wide; and when experimentally placed in water they show great distress and usually have to be rescued. While I would not totally rule the possibility that one could be taught to swim with persistent effort, I have so far seen no reports that this has ever been done.
Why this might be so is extremely puzzling. Since monkeys swim, apes must have lost this ability at some point; and humans somehow regained it. But we definitely seem to be an oddball in our little branch of the family tree.