Don’t get
me wrong, I am happy that there is something like the Quagga Project, and I
like their current breeding results. But they make a number of claims that I
simply cannot agree with. The Quagga Project pretends that they are able to –
or even did already – recreate the quagga by selective breeding with extant
Plains zebras.
They argue
that since the quagga nowadays is classified as a subspecies of the Plains
zebra it might even be only a colour variety with the only features making it
distinct being the coat pattern. Furthermore, they say that since it was not a
species on its own, the genes responsible for their colour scheme might still
be present in extant Plains zebras just have to be united. And since the quagga
displayed individual variation regarding the intensity of their stripe pattern,
a rough overlap with the original and not necessarily a total match is required
to call their results “quagga”.
“However, the extinct quagga was not a zebra
species of its own but one of several subspecies or local forms of the Plains
Zebra. This fact makes a big difference - the quagga’s extinction may not be
forever!
[The Quagga was]A variety
of zebra […]
However, since the coat -pattern characteristics are
the only criteria by which the Quagga is identified, re-bred animals that
demonstrate these coat-pattern characteristics could justifiably be called quaggas.
[…] Therefore the Quagga and other Plains Zebras
belong to the same species and consequently the Quagga should be considered
merely a different population (or deme), of the Plains Zebra.
[…]There are a few Zebras which qualify - not as true quaggas,
but as Rau Quaggas in the project. From our point of view they are
"real" quaggas, but since there has always been the possibility that
there might have been other features of the original quagga that we have not
selected for (because we do not know what those features, if any, might have
been), we have chosen the term "Rau quagga" to describe our recovered
phenotype. Rau quagga is the name we chose to apply to animals which meet the
criteria of no scorable stripes on the hind body and effectively none on the
legs (Darwin recorded occasional stripes on the hocks in some quaggas, so we
allow that in the hind legs). More will doubtless come along as time goes by...”
The project
claims that the quagga was merely a colour variant of the plains zebra as they
see no differences between the existing subspecies other than the colour. However,
there never was an osteologic study comparing the morphological similarity
between the plains zebra subspecies including the quagga. There were
craniometric measurements with conflicting results (I assume that the authors
of these studies took care of whether the skulls were from quaggas indeed or
from horses and donkeys for taxidermies) – some studies suggested that the
skulls of the quagga were nearly identical to that of other plains zebras,
while others suggested they differed from those of horses, donkeys and zebras
to the same extent. I learned from a skull gallery by Vera Eisenmann that there
is quite some variation regarding skull shape within an equine species, so that
factor might not be that important.
As to genetics,
the quagga is nested within the plains zebra. That means, it is either a member
of the species, or, if you consider it a separate species, descended from the
plains zebra at least. It seems that the quagga diverged from the other
subspecies in the middle Pleistocene [1], which is about the same time distance
as between domestic horses and Przewalski’s horses. The quagga does not share
any mitochondrial haplotypes with other plains zebras [1], but the sample size is
probably too small to ascertain whether it indicates that it was a
reproductively isolated clade on its own or did indeed represent the end of a
cline as the coat patterns within the species suggest.
Nevertheless, I
think that the divergence of about 200.000 years is too long to regard the quagga
merely as a colour variant. Genetic drift inevitably leads to changes. Apart from
that, you could argue in the same way that the hooded crow is “just a colour
variant” – we have exactly the same situation here. Furthermore, the sparce
molecular data does not give us any clue on the karyotype of the quagga – it
might have one or more chromosomes more or less than other plains zebras, as it
is the case in the Przewalski’s horse compared with the domestic horse.
We cannot say
whether the quagga had any ecological differences to other plains zebras, but I
don’t think it was necessarily the case. Not much is reported on their
behaviour, apart from that they had an idiosyncratic call was an inspiration
for the animal’s name (f.e. “kwahaa”), remotely resembling a donkey’s.
My belief is
that there is also a certain misunderstanding of the concept of a subspecies
when they say: “the extinct quagga was
not a zebra species of its own but one of several subspecies or local forms of
the Plains Zebra. This fact makes a big difference”. A subspecies is, as
the term implies, a less-marked form of a species, or as Darwin called it, an
incoming species. Everyone who has basic biological knowledge will know that
giving a clear, unambiguous definition of a species and therefore also a subspecies
is highly problematic. But what can be said is that a subspecies is not just a
result of taxonomical boredom or nit-picking, but an actual clade and defined
by biologic criteria, and this is clearly the case in the quagga. As outlined
above, there are more differences between the quagga and the remaining subspecies
than pelage characteristics, such as genetic distinctions that inevitably must
have arisen during about 200.000 years of separation, and its distinct call.
Currently there is not evidence for more as far as I know (as if it was not
enough). But the project argues that if there is no further evidence, no
further defining characters should be assumed and therefore something that
shows all traits that we know is automatically a quagga. In my opinion, the
assumption that only those distinct features that we know of through our
limited access were the only ones is ultimately destined to fail. However, the
QP does not deny that the quagga was different (and it was certainly the most
distinct of the plains zebra subspecies), but their assumption is that mimicking
those traits that were unique to it and eradicating those that differed should
lead to a true quagga.
Different
genetics and different descent, different animals. No living herd of plains
zebras do descend from the quagga in any way. The QP’s point is that all the
traits that defined the quagga might still be present in the extant population thanks
to the fact that they belonged to the same species and it likely represented
one end of a cline. I see problems in this guideline: We have no clue on the
factors that control the pelage characteristics in the plains zebra, which is
the only trait the QP is focusing on. Is it polygenetic, or regulated by one
gene only? Which characters is it connected with? No extant plains zebra has a
stripe pattern that is as reduced as in most of the quaggas, not to speak of
the brown background colour, so the selective breeding program is not working
on a fixation of a trait but on trying to achieve it in the first place from
what is not there yet. It’s like selecting for cattle with 100 cm horn length
when starting with horn lengths of 50 and 70 cm. But if I interpret the QP’s
argumentation correctly, they assume the amount of striping in a zebra’s coat
is regulated by a number of genes, and that those alleles that worked in the
quagga are split up among those we see among other subspecies, present
somewhere towards the middle of the cline. That’s a legit hypothesis, although a
speculative one.
This provides a
good opportunity to test the guideline of the QP. One could take some strongly
striped zebras from Etosha and select them for a stronger stripe pattern. Would
anybody claim that, if after some decades of breeding such a herd is as
strongly striped as possible, a Grant’s zebra (E. q. boehmi) comes out? Or taking wolves, would picking a bunch of
white or crème-coloured Northwestern wolves (C. l. occidentalis) result in a polar wolf? I think these examples
show how simplified this concept is.
However, let’s
take the QP’s argumentation for granted for a moment and say that a Plains
zebra that looks like the quagga automatically is a quagga, and that there are
no external differences other than the pelage characteristics. Do the most
advanced current results of the project look like quaggas in this respect?
Judging from the
remaining quagga skins and those individuals of the QP that I know, it is true
that indeed a number of those zebras show a stripe pattern that is as reduced
as in the quagga (apart from the legs, which are not yet totally stripeless). However,
I noticed a not negligible difference regarding the stripes on head and neck.
In the quagga, they are packed closely together, being broad while the white
space between them is thin. And there are no thin stripes between broad stripes
as we see it in many extant zebras. In the zebras of the QP, the exact opposite
is usually the case. I even get the impression that as stronger reduced the
striping on the rear is, the more it is on the face as well. The facial stripes
in the quagga on the other hand were very broad and intense, giving the head a
dark aspect overall.
The QP admits
that there has been only little progress in achieving a brown background colour
on the trunk. This might change in future generations, but maybe not. Maybe the
last few stripes on the leg will disappear, but maybe not. Perhaps the climax
is reached already, only future will tell. But I see no trend towards the
quagga regarding the neck and facial stripes. And it brings us to an empirical
problem: when is the breeding program progressed enough to say: “ok, this and
that trait have not been achieved”? The predictions made have to be
falsifiable, otherwise they are of no empiric value. No such timeline has been
given, and apart from that, how stable have the characteristics to be in a
“recreated quagga population”?
So my
conclusion is: Their claim that the quagga was merely a colour variant of “the”
plains zebra is likely to be erroneous, their assumption on the genetic
background of the stripe pattern is speculative, their guideline that one subspecies
can be turned into another by selective breeding on external traits is
simplified and probably wrong as my examples have shown, the resemblance of
their current results to the quagga are not satisfying yet (contrary to what
the QP says) and the resemblance to the quagga is only limitedly falsifiable following
their concept.
Perhaps the
reason for them considering their results recreated quaggas is just for public
relations, but I fear that it is the same kind of self-delusion as it was the
case with the Heck brothers. They officially call them Rau quaggas to
appreciate that there “might” have been further differences, just as some
people call Heck cattle a “model” of the aurochs. But this is not legitimate in
my view: There can be no man-made alternative versions of wild animals by definition. Heck cattle is not a
model of true wild-type aurochs (not more than any domestic cattle breed is),
and the zebras of the QP are not more of a quagga than other Burchell’s zebras
are, despite some resemblance in the coat pattern.
This is why I
call those zebras “Rau zebras” instead of “Rau quaggas”, as you might have
already noticed.
Literature
[1] Hofreiter et al.: A rapid loss of stripes: the evolutionary history of the extinct quagga. 2005.
