The URL of this Ferret Health List message is:
http://groups.yahoo.com/group/Ferret-Health-list/message/13238
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
[Posted in FML issue 3793]
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