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Derek Bickerton

Derek Bickerton

The Hyrax, the Elephant and the Dugong

Apes aren't necessarily the best models for explaining humans.

The hyrax is a small terrestrial mammal weighing between 2 and 5 kilograms. The elephant is the largest terrestrial mammal, weighing anything from 4,500 to 11,000 kilograms. The dugong is a midsized marine mammal weighing from 150 to 300 kilograms.

The hyrax has four legs but no trunk and small ears but no tusks and no trunk and no tail. The elephant has four legs and enormous ears and two tusks and a trunk and a tail. The dugong has no legs and no tusks and no trunk and no external ears but has two flippers and a tail that differs so radically from the elephant's tail, it's a wonder we use the same word for both.

The hyrax, or at any rate the best known kind, the rock hyrax, lives in rocky areas in Africa and the Near East. The elephant lives pretty much where it feels like throughout India and East Africa, though it is perhaps fondest of wallowing in swamps. The dugong lives in warm, relatively shallow waters along the shores of the Indian Ocean and into the Pacific around New Guinea.

The hyrax is pretty omnivorous, eating grass, leaves, insects, fruit, birds' eggs, lizards, and grubs. The elephant is strictly herbivorous, preferring to browse on the bark, leaves and fruit of trees, but able to handle grass if there's nothing else. The dugong eats little apart from sea grass, which it uproots from the sea bed with its snout.

Looking at these details only, you could be pardoned for concluding that hyraxes were rodents related to prairie dogs, with which they share the behavior of posting sentinels to warn of predators. You might suppose that elephants were closely related to other large tropical herbivores with thick skins and a penchant for wallowing in swamps, such as hippopotami. And it might seem reasonable to guess that the dugong had its closest connections with other marine mammals, sea-lions or dolphins.

You'd be wrong. Hyraxes, elephants and dugongs are more closely related to one another than to any other living animal.

Well, that's not exactly true. The closest surviving relative of the dugong is the manatee, a fresh-water, New-World version of itself. Apart from this, and the fact that there are two species of elephant and several of hyrax, it's absolutely true. Hyraxes, elephants and dugongs evolved from a single common ancestor.

What on earth can any of the above have to do with psychology, or humans?

Plenty. These facts show how wrong it can be to assume that just because species are closely related they will resemble one another. Yet when it comes to us and our closest relatives, we make the assumption unquestioningly. We turn to those relatives--chimpanzees and bonobos--and use them as our models, seeking in them precursors for even our unique behaviors. This assumption is epitomized in the titles of books about our species: The Talking Ape, The Naked Ape, The Third Chimpanzee, The Ape that Spoke.

How confident would you feel if you were told that a good book about dugongs was The Aquatic Hyrax? Or that a thorough explanation of elephants was found in The Dugong that Never Forgets?

Ah, you will say, the comparison is absurd. The last common ancestors of ourselves, chimps, and bonobos may have lived as little as five million years, ago so we can't have changed enough to make apes a misleading model. Whereas the last common ancestor of hyraxes, elephants and dugongs may have lived as much as fifty million years ago. In the latter case, there might have been time for gradual changes to produce very different animals. But there hasn't been time for us to change much from other apes.

However, there are at least two good arguments (and no good contrary ones) for assuming the two cases aren't so different after all.

One stems from the nature of evolution--it goes in fits and starts. Whether you want to call it Stephen Jay Gould's "punctuated equilibrium" or Richard Dawkins' "variable speedism" (a classic case of explaining by renaming), it is inconvenient but a fact that new species develop in a relatively short space of time (short in evolutionary terms, that is), and that afterwards they change little for relatively long periods. (There is now a good explanation for why this is so, called niche construction theory.)

The other relates directly to the species concerned. The order in which hyraxes, elephants and dugongs evolved remains unclear, because the mitochondrial, molecular and other genetic evidence points in more than one direction. In the words of one group of specialists, "These discordant results suggest that the species diversification event that defined the three orders of Paenungulata occurred over a relatively short evolutionary time period."

Interactions with varying environments bring results quite quickly, and affect the resulting phenotypes as much as genes do. Small social mammals that live in rocky crevices or burrows in predator-infested terrains will soon develop a system of sentinels and alarm-calls, like hyraxes and prairie dogs did, regardless of whether they are closely or only very distantly related. Mammals that take to the sea will soon turn forelegs into flippers and fuse back legs into massive tails, regardless of their ancestry, just as dugongs and sea-lions did. The environments in which these animals chose or were forced to live, rather than genetic factors, best explain why hyraxes, elephants and dugongs became so different from one another. Isn't it equally likely that environmental factors rather than genes have shaped ape-human differences, making apes poor models when it comes to explaining more complex forms of human behavior?

Don't get me wrong. Many profound resemblances do link apes and humans, in physiology, emotions, and forms of social behavior. But in the things that make us most distinctively human, we are different. We have language, but apes have nothing remotely like language. We have cooperation on a massive scale, unequaled anywhere outside the hymenoptera, while apes aren't at all cooperative. So seeking among apes for precursors of these behaviors makes no more sense than claiming elephant wallowing as a precursor of dolphin swimming, or the dugong's rooting snout as a precursor of the elephant's prehensile trunk.



About the Author

Derek Bickerton

Derek Bickerton is emeritus professor of linguistics at the University of Hawaii; his most recent book is More Than Nature Needs: Language, Mind, and Evolution.