From:
Church, Robert Ray (UMC-Student)
Date: 2002-05-24 02:23:00 UTC
Subject: Bob C: The LONG Road to Domestication (Or post...)
Q: "Can you please be more specific regarding the ancestor [the
progenitor] of the ferret? Are they Mustela putorius furo or not?
Inquiring minds need to know."
A: Yeah, yeah, sure. You probably thought the Bat Boy was real, didn't you? ;-)
Little differences sometimes just make little differences?
If you don't want to read this long explanation of ferret domestication, just call domesticated ferrets Mustela furo and skip the rest. Ready for the tech stuff? Ok, I'm going to be a bit more technical here than usual, but will be as brief as possible. The domesticated ferret (Mustela furo) has a diploid chromosome number 2n=40, which is identical to the European polecat (Mustela putorius). The steppe polecat (Mustela eversmanni) has a diploid chromosome number 2n=38, which superficially sounds like a big difference. However, the difference is a due to a single Robertsonian rearrangement. In the past, some controversy existed to whether the difference in chromosome numbers was due to a Robertsonian rearrangement or to a centromeric fission (the creation of two chromosomes by the splitting of one at the centromere), but current research suggests the difference was caused by a centromeric fusion.
Simplistically, a Robertsonian rearrangement is a fusion of two acrocentric chromosomes that fuse near the centromere, forming a single chromosome when there were once two. An acrocentric chromosome is one where the centromere is at or near the end of the chromosome (the centromere is where the kinetochores lie, which are the chromosomal attachment points for the spindle fibers, used in cellular reproduction). There is generally no difference in the genetic information, so even though the steppe and European polecat have different chromosome numbers, they have essentially the same genetic information. This is why the domesticated ferret and the two polecats are fully interfertile and produce sexually viable offspring. To complicate the issue are black-footed ferrets (Mustela nigripes) who also have a diploid chromosome number of 2n=38, and are also fully interfertile with the domesticated ferret, and the steppe and European polecats.
Recent research (Davison et al., 1999; Kurose et al., 2000) has found the genetic distances between the European and steppe polecats to be about 0.3 to 0.6% with 94%/87% bootstrap values. If you think this is small, you are very correct. It is smaller than found between various subspecies of American martens, and much smaller than the distances found in Old and New World populations of elk, badger, wolf, wolverine, reindeer (caribou), and sea otters (to name a few species that I have these types of values on hand). Understand, what this means is that animals that are considered to be the same species--even though they live in widely separated locales--have MORE genetic distance than found within the members of the polecat group. Ah, the complexities of defining species!
When genes don?t fade?
The research also suggests the separation between the various polecats is less than a million years (maybe even half of that). This sounds like a lot of time, and it is when you are talking about humans; most of the really exciting stuff in human evolution occurred in about the same time frame. However, humans are an exception to the rule. The Mustelidae is a very conservative group; although what we consider to be species have changed over time, the basic animal has changed little. This means the genetics of polecats is highly conserved, and changes very little over long periods of time. In other words, the ancestor of modern ferrets and polecats, while clearly a different species, wouldn't look or act much different than the modern species.
Run the data up the polecat and salute?
Ok, what does this mean regarding the domesticated ferret? It means trying to, er, um, ferret out the progenitor will be extremely difficult. Both Davison and Kurose were unable to determine the progenitor of the domesticated ferret because the relationships between the species lack appreciable genetic distance. This is extremely significant, because it means previous proof tying the progenitor to the ferret (their karyotype morphology), has lost significance, requiring further in-depth investigations. At this point in time, we do not know which polecat was the progenitor of the domesticated ferret, forcing a return to the Mustela furo binomial. See? Now you lucky ones who waded through these pages of techno-jargon not only get to use Mustela furo, but now you also know why! Aren't you glad you didn't stop at the top?
It also throws into question the exact relationships between the polecat groups. If the genetic differences between the steppe and European polecats are due to centromeric fission, that is the splitting of a single chromosome, it would imply the steppe polecat was first (or their immediate ancestor), and the European polecat was the offshoot. However, if the differences are due to a Robertsonian rearrangement as thought, the implication is that the European polecat (or immediate ancestor) gave rise to the eastern form. Since we are certain the black-footed ferret is an offshoot of the steppe polecat, current data suggest the phylogeny of the polecat group would have the European polecat (or immediate ancestor) giving rise to the steppe polecat, which then resulted in the American ferret. Why is this critically important? Because there is a lack of ANY zooarchaeological evidence that would support a location of origin for the domesticated ferret.
Ferreting out the progenitor?
Are you ready to get REALLY confused? Assume the Robertsonian rearrangement in the steppe polecat is correct. That would imply they evolved from either the European polecat or a common ancestor. Superficially, it would also imply the European polecat was the progenitor of the domesticated ferret, based on a shared diploid chromosome number of 2n=40. However, that is not necessarily the case. Domesticated species are initially developed from very small populations, which means they are subject to various degrees of founder?s effect. It is entirely possible that the progenitor was the steppe polecat, but early during domestication, centromeric fission took place, increasing the diploid chromosome number of 2n=38 to 2n=40. If a Robertsonian rearrangement could fuse two acrocentric chromosomes with little resulting difference, then a centromeric fission could easily reverse the process as well. OooOOo. Genetics is cool!
Another possible explanation is that domesticated ferrets are the result of domestication of BOTH polecats. In this hypothesis, both steppe and European polecats were domesticated, and the domesticated ferret is some sort of hybrid between the two. There is some evidence for this idea. In early genetic studies of the domesticated ferret, diploid chromosome numbers for the ferret reportedly ranged from 2n=38, 2n=39, and 2n=40, exactly what would be expected if hybridization took place. This type of variation might also be seen if a Robertsonian rearrangement or a centromeric fission took place, but the event has not stabilized within the population.
Finally, the Robertsonian rearrangement hypothesized for the steppe polecat may be in error, and instead, the European polecat resulted from a centromeric fission in the karyotype of the steppe polecat. You never know.
When carnivores go domestic?
For every action, there is an equal and opposite reaction. That really has nothing to do with the domestication of ferrets, but the science of domestication lacks such easily understood and quotable laws. But there are two laws that are as universal as they come: 1) animals are never domesticated outside of their natural range, and 2) animals are domestication for a clear and purposeful reason. This means ferrets were domesticated someplace where polecats lived, and they were domesticated for a specific purpose.
No chance the ferret was domesticated in Egypt. No polecats have ever been found there; not now, not during the time of the domestication, not during the ice age, and not even during the last million years. Remember the significance of that time? That means that no polecats have been in Egypt since they evolved. This breaks the first ?law? of domestication, but what about the other, that of purpose? Ferrets were domesticated to protect grain stores?their job was that of mousing. The Egyptians already had cats, and cats are MUCH more efficient at mousing, which is why cats took over the job throughout Europe.
Egypt? My mummy says no?
Egypt is the key to the entire domestication issue. While the Egyptians never domesticated the ferret, Greeks, early Romans, and Phoenicians who saw cats, and knew what they could do, visited them. There was no comparable animal in the northern Mediterranean; that is, Europeans lacked a domestic animal that could be used to hunt mice secreting themselves in grain stores or aboard ships. The cat, sacred in Egypt, was not let out of the country, so Europeans looked for a substitute (a few might have been smuggled out, but not in numbers enough to create viable populations). The local wildcats were unsatisfactory?if you have ever picked up a pissed feral cat, you have a minor idea of the consequences of picking up a really pissed European wildcat. But European polecats were common, they were easily tamed, and they served the same function. They were a perfect alternative.
What this means is, ferrets were initially domesticated to mouse, not to hunt rats or rabbits. Am I sure? Well, at this point in time, European rabbits were localized to the Iberian Peninsula?they were not even near the Mediterranean at the time (rabbits weren?t even domesticated until the Middle Ages). Rats were still in Asia, and it would be another thousand years or so until the first of the really nasty plagues. However, there is a little known aspect of early domestication few consider--hamsters. European hamsters were found throughout Europe at this time, and are commonly found as food refuse in archaeological sites. The hidden aspect to ferret domestication could be their use to obtain hamsters for human consumption. So far, such conjecture is exactly that, but it answers some previously unanswered questions (why did ferrets remain domesticated after the introduction of the cat?), and helps to explain how the ferret would have easily fallen into a rabbiting role as bunnies colonized Europe.
Eddie Murphy had nothing to do with Trading Places ?
Remember all that technical stuff slathered on your screen at the beginning of this post, so very, very long ago? The reason it was so important is because it offers an important clue to the entire puzzle. Remember I reported researchers couldn?t determine the progenitor of the ferret? That doesn?t mean they couldn?t isolate populations of steppe polecats from European polecats. Think about the implications for a moment. If ferrets descended from steppe polecats, you should be able to group them together. The same would be true of European polecats. Using the rule of parsimony (the simplest solution being the most correct), one of the simplest solutions for why the progenitor cannot be found is exactly what both research groups already suggested: hybridization.
?But, how,? you may ask, ?can people breed animals that live thousands of miles apart during a time when most people never traveled more than 30 miles from their home?? Get in your time machine and think back to the part in this post about why the Egyptians did not domesticate the ferret. Remember who was involved? The Phoenicians, Greeks, and early Romans? If you chart the historic locations mentioned in the early historic documents, they tend to line up on Phoenician trade routes, which spanned the Mediterranean from Turkey to Spain. While we classify polecats into two species, our viewpoint is different than that of early peoples who probably saw them as the same. They could interbreed, so why think differently? It is highly likely that domestication was more-or-less unintentional, occurring only because early domesticators bred to make polecats tame, not to change their morphology. Remember, what the early domesticators wanted was an animal that did the same thing as a polecat, only one friendly to humans.
Similarly, it is unlikely early domesticators would suddenly come up with a different name for these early ferrets, probably calling them by the same name as their progenitors, explaining why early Greek references (Aesop, Aristotle, Aristophanes) use the same name for ferret as for polecat. We do the same thing; the American mink was domesticated during the last century, and we still call it a mink. The same is true for turkeys, cavies, hamsters, lab mice and rats, hamsters, and little bitty bunny rabbits, among others. Language is highly conserved, and rather than looking at new names to infer domestication, it is more important to look at intent.
The Bottom Line on Bottom Scooters?
Arguments that ferrets were domesticated from any specific subspecies of polecats are moot. Current accepted scientific classification does not recognize subspecies of European polecats (the exception being the use of Mustela putorius putorius to distinguish them from domesticated ferrets, Mustela putorius furo, a classification that?in light of recent studies?is no longer supported). Some recent researchers have suggested the ferret is descended from specific populations of polecats, such as the Moroccan population of European polecats (the only polecat in the extreme north west of Africa?the so-called Barbary polecat). Such studies are based on skeletal morphology and subject to tremendous error. If skeletal studies could not prove the progenitor in the past, why would they now? The main problem with skull studies are that the process of domestication changes skull morphology, as well as such factors as diet and caging. Unless these factors can be controlled, the data resulting from such studies are unreliable.
You can draw a parallel to the Neandertal problem in human evolution. Based on skull morphology, various scientists argued Neandertals were an ancestor of modern humans. Recent genetic work has falsified this hypotheses, suggesting skeletal similarities are correlated to similar functions, and not necessarily direct ancestry. To argue ANY one subgroup of polecats are the progenitor of domesticated ferrets based on skull morphology is simplistic. Some types of evidence carry more weight than others, and in this case, the genetic evidence is overwhelming, and far more reliable than skull morphology.
Here it is, the end of the lineage?
My hypothesis is that ferrets were slowly domesticated over several centuries by a combination of Mediterranean peoples (primarily Greek, Phoenician and early Roman), for use as mousers aboard ships and in homes and granaries. Traded throughout the Mediterranean, the early-domesticated ferret was hybridized with both the steppe and European polecat, collected from different locales. As cats were slowly introduced into a Late-Roman Europe, ferrets lost favor in mousing, but weren?t abandoned (like early attempts to domesticate the mongoose). Instead, they were used to hunt hamsters, and later, rats and rabbits. While the occasional person may have owned a ferret or two as a pet, they were primarily working animals until the 1970s, when their popularity as pets became paramount.
Ask a simple question, get a simple answer...
Bob C