For more than a century fossil horses have stood as some of the most iconic examples of evolutionary change. From about 1870 onward it seemed that the ancestry of modern horses was represented by a nearly complete fossil series, but this is not to say that we have always perfectly understood these remains. Even though It was initially thought that Europe was the cradle of horse evolution this idea was undermined by numerous discoveries from the American West. The early evolution of horses had occurred in North America, and a slew of fossil genera made it easy to present horse evolution as one of straight-line progressive development. Even if paleontologists drew branches in their phylogenies when communicating to their colleagues the public was presented with a more straightforward, and ultimately inaccurate, representation.
Indeed, horses were one of the first vertebrate groups for which a relatively continuous fossil series was known, but by the 1920's other groups were just as well-represented. Camels were one such group. Much like horses their living representatives were native to Africa and Asia but the group had initially evolved in North America. In this way camel evolution seemed to be an artiodactyl parallel to horse evolution, so much so that many authors simply said that the camels were following the same evolutionary trends as horses (increasing size, reduction of toes, etc.).
If paleontologists agreed that camel evolution was as well-understood as horse evolution, why are so many people unfamiliar with the ancestry of camels? I cannot say for sure, but there are probably several contributing factors. The first is that horse fossils were being popularized as representing a relatively complete evolutionary series before the North American fossils became well known. In an 1870 lecture on paleontology T.H. Huxley pointed to horses as the one mostly-complete fossil series that showed a direct line of descent from smaller, multi-toed browsers to large, single-toed grazers.
Horses were already well-established as evolutionary icons by the time camel evolution became as well documented. This is significant as it was thought that camels followed an evolutionary trajectory similar to that of horses. As stated in A text-book of geology for use in universities;
The two families of camels and horses each arose in a single series. This monophyletic condition continued through the Eocene and most of the Oligocene, but in the later Oligocene and more markedly in the Lower Miocene the camels and horses branched out, each in their own fashion. In a general way, they kept quite an even pace in their advance from the more primitive to the more specialized condition.
This similarity made it seem unnecessary to cover their evolution in the same detail. In three 1920's biology and paleontology textbooks (A text-book of geology for use in universities, General biology, and Principles of animal biology), for instance, a sections on camel evolution are placed adjacent to ones about horse evolution. The sentiment expressed in each, however, is that camel evolution is not be covered in much detail given its similarity to horse evolution.
It appears that camel evolution was understood too late and was too similar to horse evolution to be of much special interest, but I wonder if the preference towards horse evolution has more to do with domestication. Horses were the favored domestic service animal in Europe and North America; they were very familiar animals that were essential to farming, transportation, etc. Perhaps popularizers of science thought that evolution would appear as a more "real" concept if the ancestry of such a familiar and beloved animal could be traced.
Camels, by contrast, were unfamiliar. People in Europe and North America might know of them but would not encounter them unless visiting a zoo or circus. If camels had been our favored beasts of burden or evolutionary studies had percolated in an area of the world where camels were more familiar, though, perhaps then their evolution would have received greater attention. If true this may also explain why the ancestry of elephants and rhinos have traditionally taken a back seat to horses in popular summaries of evolution.
This is all speculative, of course, but it is profitable to ponder methods of science popularization. Why do we favor certain groups of examples of evolution and not others? Why are horses considered better examples than camels, elephants, rhinos, etc.? Why do popularizers of science seem to reinforce these roles rather than alter them (or offer interesting alternatives) as new evidence comes to light? Perhaps no concrete answers are available to these questions, but they are worth mulling over.
- Log in to post comments
More like this
I think the key words are "popular summaries of evolution."
Looking at the illustration of the evolution of camel limbs, the changes appear - to this layman - less dramatic than in similar illustrations of the evolution of horse limbs. I'm not suggesting that the changes aren't as dramatic when viewed with a trained eye. However, for the purposes of demonstrating evolutionary processes to a relatively untrained audience, equine anatomy (with its transition from five digits to one) may be a more effective example.
I completely agree. When I was younger, I thought horses were the only examples of "evolution in action", because it was in all the books and at all the museums. Horses are one of the most well known animals (too well known for my taste; no-one's ever heard of a Przewalski's horse, but they know every breed of domesticated horse going), so it may very well have something to do with its prominence. It might have something to do with the five toes into one thing, which is really easy to see in the Hyracotherium to Equus example, whereas the camels above is only four into two.
Martin- Toe reduction in horses might be a little more dramatic, but here is the question; is the camel illustration less dramatic because that part of the transition was less well known or because the illustrators didn't bother to sketch it in more detail? A similar though occurred to me, but I think our preference for horses goes beyond toes.
Hey, not only have I heard of Przewalski's horse (aka the Takhi), but I've known of this wild horse about as long as I've known about the domestic variety. I was pleased to hear that it's been successfully re-introduced into its native habitat in Mongolia.
Because if we explained evilution using camels, we'd be terrorists as well as communists?
I didn't know that there were camels (or their ancestors) in North America. Knowing my kids, I think they'd find that fascinating.
But Steve Gould gives an answer in Wunderful Life (your current reading):
To be an ideal "icon of evolution" the camel series needs a sole survivor which plays the role of the current crown holder while all the extinct taxa which do not fit well into the "march of progress" form "side branches".
If I have several survivers that are quite distinct in their appearance (e.g. the three genera of Camelidae), who is the crown holder and who belongs to a side branch?
Interesting. When I was a kid, I think perhaps the first illustration of an evolutionary tree that I ever saw was in The How and Why Wonder Book of Prehistoric Mammals -- and there were two: one for horses, and one for camels!
But overall, in my continued reading as I grew up, the horse example was indeed referred to much more often. I think it is a combination of the factors that have been mentioned above:
1) The reduction to one toe in horses is a more dramatic example than the reduction to two toes in camels.
2) The evolution of the horse appears to be an easier story to tell and to illustrate -- basically, horses got bigger and lost their extra toes. But with camels, you had llama-like forms and one-hump dromedaries and two-hump Bactrians, in addition to the giraffe-like Alticamelus forms that became extinct.
The horse's story is also easier to tell in terms of what it was being adapted "for" -- faster running, and the ability to eat tough grasses. In other words, to live on the plains. Whereas the story of the camel's adaptations is more complicated because we don't have any fossils that definitely indicate a progressive growth in the size of the hump, for example. And besides, various camelids adapted themselves to being hot desert dwellers, colder desert dwellers, pampas/plains dwellers, mountain dwellers, high tree browsers -- it's almost as if their evolution had no particular direction or purpose! ;)
3) Horses are a more charismatic domestic animal -- e.g., often portrayed in the Western TV shows of my youth as possessing doglike levels of intelligence, affection and loyalty, whereas everything I'd heard about camels in my youth was that they were ill-tempered, stubborn, and if they became sufficiently annoyed they'd spit nastily on you.
So overall the story of the horse was both more dramatic and simpler to tell, as well as featuring a more attractive protagonist.
To clarify: The How and Why Wonder Book of Prehistoric Mammals showed the evolutionary trees for horses and camels side by side, on facing pages.
Oops, I just learned that Alticamelus is now Alticamelus. It seems all the cool prehistoric animal names that I learned as a kid have been replaced with other names that are either less cool or more complicated. First it was Brontosaurus, then Dinohyus, then Brontotherium ... I'm afraid that if I turn around, Smilodon will be replaced by something lame like Californiatherium or something.
Dammit! That second "Alticamelus" was supposed to be "Aepycamelus."
It is because there is a book, "Horses", by George Gaylord Simpson. Some years ago, I gave my father, who cowboyed all his life, a copy. He enjoyed it. Because Simpson was knowledgable about modern horses, people who knew about modern horses probably were inclined to accept what Simpson said about horse evolution. If there is a similar book, "Camels", I am not aware of it.
Brian:
Or, on a related note: when equid evolution is illustrated in popular works, why is the 'end product' always the horse rather than a donkey or a zebra?
Camels are thought of as exotic animals, but the mainstream view now seems to be that they evolved in this country. What makes camel evolution in North America so fascinating is it's diversity, from delicate, gazelle-like stenomylus to aepycamelus, the towering, giraffe-like browser. Perhaps the greatest difference is that, unlike horses, camels aren't thought of as "American" animals, even though until relatively recent history, that's just what they were.
Horses get all the attention because horses are charismatic animals.
Martin, not only are you a tro9ol
but you're a tool. And a wanker too. What in flaming hell is wrong with you.