Canis lupus hominis

The answer to this “Identify the Species” query is that this animal is the wild guinea pig.

It the ancestor of the domestic guinea pig.

The name of this particular animal varies depending upon the source, but its scientific name is (Cavia tschudii). I have called it Tschudi’s cavy or the Montane guinea pig.   In Spanish it is called cuy silvestre.

For many years, the actual ancestry of the domestic guinea pig was in dispute.  In the end, there were two candidates:  the cuy silvestre or the Brazilian guinea pig (Cavia aperea).

The Brazilian guinea pig is not found in the Andes, where much of the archaeological evidence for early guinea pig domestication has been found. It is generally found from Argentina and Uruguy to Colombia.

However, it more strongly resembles a domestic guinea pig than tschudii.

The Brazilian guinea pig (Cavia aperea).

The Brazilian guinea pig has a very similar head shape to the domestic guinea pig. Both of them have relatively narrow, flat skulls.

However, when Brazilians were bred to domestic guinea pigs, there were fertility issues after several generations. This strongly suggested that these two animals are not the same species, and that the Brazilian guinea pig is not the ancestor.

But the other candidate didn’t look as much like the domestic guinea pig as the Brazilian cavy.

When I pondered the question a few years ago, I didn’t know which species it was. I thought science had come up with only confusing  and contradictory answers to this question.

I was wrong.

In 2007, there was an important comparative study of guinea pigs and their wild relatives. This study used several molecular analyses of the cytochrome b gene, which is part of the mtDNA, and 12S rRNA, which is expressed through a gene that is encoded in the mtDNA, that were taken from modern European and criollo (Andean landrace) guinea pigs and wild cavies and their relatives. All the molecular analyses pointed to tschudii being the ancestor. The authors then compared the morphology of the Andean and European guinea pigs with wild tschudii and mummified guinea pigs from the Pre-Columbian Era. The transition between wild tschudii and the domestic guinea pig could be detected in the mummies, as well as in the difference between Andean and European guinea pigs.

Granted, this particular study examine only a narrow portion of mtDNA, and it is possible that aperea could have played some role in developing the domestic guinea pig after all. However, in terms of their mitochondrial DNA inheritance, guinea pigs are tschudii.  The fact that much of the archaeological evidence for guinea pig domestication is in the Andes also points to this species.

However, as I noted, tschudii doesn’t look that much like a domestic guinea pig.

Here is tschudii in profile:

Here is a domestic guinea pig of the European type. It happens to be of the agouti color:

Note that the domestic guinea pig has a somewhat more pointed, narrower skull  that the wild tschudii.

The domestic guinea pig looks more like the aperea in the color photo than the tschudii, so one can see why it was thought to be the primary ancestor.

The authors of the molecular and comparative morphology study provided several photos of x-rays of guinea pig skulls, so we can actually see what the transition from wild tschudii to modern domestic guinea pig looked like.

C. Wild tschudii. D. Pre-Columbian guinea pig mummy. E. Andean domestic guinea pig. F. European domestic guinea pig.

The authors very quickly point out that the brain case in the domestic guinea pig has been dramatically reduced through domestication.

But I noticed something else from their skull specimens.

The “muzzle” part of the guinea pig has actually become longer and more pointed through domestication. You can see it in the photo the live specimen, but it’s more clear in the x-rays.

Also, guinea pigs have been selectively bred to be much larger than the wild tschudii. European boar guinea pigs are nearly twice the size of their counterparts in the wild. Even the Andean criollo guinea pigs are significantly larger. This makes sense, for guinea pigs were originally bred for food. If you want to breed something for food, you want to make it larger.

But a more pointed skull and larger size are not the features we have been told are associated with domestication.

The current domestication literature sees all domestication as resulting from juvenilization. All domestic animals are thought to be neotenous when compared to wild animals, and neoteny is thought to be the process through which domestication took place.

However, with guinea pigs, we have a major problem, for the only supposed neotenous that guinea pigs possess in domestication is a  significantly reduced brain size.  The brain size issue is a very poor example of neoteny, for one can see how domestic guinea pigs evolved smaller brains. They were bred for generation after generation in an environment that lacked both predators or a need to forage, and the selection pressures that worked upon the population to maintain a larger brain simply weren’t there. This is probably why most domestic species do have smaller brains than their wild counterparts. Brains cost a lot of energy to maintain, and if you don’t need to have heightened sensory abilities to survive, the brain size will start to decrease over the generations.

But the other features are hardly the result of neoteny. The authors of the guinea pig study provide x-rays of the skulls of juvenile guinea pig mummies.

C-E are juvenile guinea pig mummies. F is an adult.

One can see that the skulls of the juvenile guinea pig more closely resemble that of tschudii.  The wild form has the neotenous skull.

Now, there are several species of domestic animal in which the domestic form is on average larger than the wild form. Domestic pigs are often much larger than wild boars, and horses, on average, are much larger than the extinct tarpan.

But with guinea pigs, the wild ancestor is not only smaller, it has a more juvenilized skull.

The guinea pig strongly suggests that neoteny is not the process through which domestication takes place. With the guinea pig, domestication resulted in the species developing features that more strongly resemble another species of cavy, which is strange in itself.

Domestication is the result of a much more complex series of selection pressures than neoteny.

With guinea pigs there was a selection pressure for size in Andean villages, which then became even more intensified in the European and North American pet and laboratory market. There was a relaxation of selection pressures for a large brain, which may be related to the narrowing of the muzzle.

One can describe those pressures very well without every going into a discussion on neoteny.

Neoteny is not some magical process of domestication, even though it appears that many people think it is.

The reality is much more complex– as one might expect.