dubois@uwmacc.UUCP (Paul DuBois) (05/01/85)
In response to some of Ron Kukuk's postings, two or three people have
given the dog as an example of observable evolutionary change.
Certainly they appear to vary widely. In reply, I offer the following.
It should not be supposed that any or all of the authors cited below
would agree with my conclusions.
Here's what creationists Duane Gish and Frank Marsh have to say:
Gish [pp25-26].
"Another example familiar to all of us is that of the dog. All of the
dogs, from the tiny Chihuahua to the Great Dane, and from the bulldog to
the greyhound have been derived from a single species, _Canis
familiaris_. The process has been exaggerated by man, of course,
through artificial selection and inbreeding."
Gish recognizes here the importance of inbreeding in producing variation
among breeds.
Marsh [p352].
"What man has accomplished in the development of different breeds of
dogs is indicative of the potentialities which may lie within all kinds
of animals. It is almost more than we can comprehend that the toy
poodle and the wolfhound are blood descendants of the same ancestor.
Not only in external morphology but in mental differences the same wide
variation is shown. We recognize the terrier's propensity for digging,
the spaniel's curious love for water, and the tenacity of bulldogs. We
recognize great mental differences between greyhounds and hounds,
between both of these and collies, and between all three and bulldogs.
And still the fact stands that they manifestly had the same ancestor.
Their origin through mutation and through processes of hybridization
within the dog kind is a historical fact."
Now, these are statements by creationists and so are likely to come
under special scrutiny by evolutionists. Let us examine what
evolutionary writers have to say on the subject.
---
Above, Marsh recognizes the importance of mutations in producing
variation among breeds. The nature of some of these mutations is
clarified by Goldschmidt.
Goldschmidt [pp279-281]
"[Stockard] pointed out that a considerable number of breeds of dogs are
of a pathological type which closely resembles the type of well-known
abnormalities caused in mammals and man by hormonal insufficiencies or
imbalance. Such forms as the St. Bernard, Great Dane, bulldog, and
dachshund fall into this category, showing in growth habit, skeleton,
and instincts the conditions known in pathology as achondroplasia,
dwarfism, gigantism, acromegaly, all caused by abnormal endocrines.
These racial traits in dogs are certainly hereditary and they are based,
as far as information goes, upon relatively simple Mendelian
conditions."
The role of mutations in contributing to this variability, then, is
deteriorative. This is demonstrable.
Grasse', too, indicates that some of the variability of dogs is achieved
by selection of mutations, and points out that these cannot be
considered analogous to the products of natural selection:
"The products of domestication deviate more or less from those found in
free nature and sometimes border on monstrosity. It is hard to
visualize how lapdogs, Yorkshire terriers, or Pekinese could survive in
the wild. Certainly they would not last long in the woodlands or
pasture of our temperate zone" [p122].
[p124] "The range of dog breeds is even wider because selection has
taken place in different ways, according to esthetic value or oddity,
aptitudes for hunting, and use as watchdogs. Thus, a great many
mutations more harmful than useful to the species have been maintained."
So, much of the variability of dogs is achieved by maintaining
"mistakes". To a certain degree then, if one maintains that dogs are an
example of speciation in progress, one maintains that the process is
brought about by genetic decay and deterioration. Shades of Wiley and
Brooks!
Even so, it must be recognized that dogs do vary widely. This is
obvious. But what is the nature of this variability? It is clearly at
least morphological. Is it more than that? I must admit that to me it
does not appear so.
Grasse' [p124] "All of these breeds, however different from one another,
cross-breed readily without loss of fertility... From all this it is
quite clear that dogs selected and kept by man in a domesticated state
_remain within the boundaries of the species_."
Also, Goldschmidt [p178] reports fertile crosses between wolf and dog.
(At first sight this would appear to invalidate the observation made by
one person on the net, that domesticated dogs are distinct from all wild
species, since such a cross would violate the criterion for biological
speciation (i.e., reproductive isolates). This may not be true,
however, since the study cited by Goldschmidt came out of Russia in the
thirties. It may not, therefore, be trustworthy. My impression is that
Soviet science in the earlier part of this century is not (and for good
reason) held in very high regard. On the other hand, the study may be
perfectly valid. I don't read Russian, though, so I can't check it
out.)
[p125] "Ten thousand years of mutations, cross-breeding and selection
have mixed the inheritance of the canine species in innumerable ways
without it's losing its chemical and cytological unity. The same is
observed of _all_ domestic animals."
"The changes brought about in the genetic stock affect appearances much
more than fundamental structures and functions. In spite of the intense
pressure applied by artificial selection (eliminating any parent not
answering the criterion of choice) over whole millenia, no new species
are born. A comparative study of sera, hemoglobins, blood proteins,
interfertility, etc., proves that the strains remain within the same
specific definition. This is not a matter of opinion or subjective
classification, but a measurable reality." [This would not hold for
plants, of course - pd.]
The upshot of what Grasse' says is that artificial selection is
different than natural selection (which point several of you have
observed). But he also points out that natural selection tends to have
a stabilizing effect. Man can produce variability by design. Nature
restricts it.
Patterson [pp11-12]
"The most striking example of variation in domestic animals is surely
the amazing range of dogs. Darwin thought that the various breeds of
dog were descended from several different wild species. He gave no good
reason for this opinion, and it seems that he was simply unable to
believe that a single species could be the source of such variety.
Modern opinion is that the domestic dog descended from the wolf, _Canis
lupus_. Archaeological finds prove that dogs have been domesticated for
at least 14 000 years. We do not know whether wolves were domesticated
once or several times, or where the original domestication took place,
although it must have been in the northern hemisphere, the home of the
wolf. Dogs have since been distributed all over the world by man, and
in many places they have escaped and assumed the status of a wild
species, like the dingo in Australia.
"So men have been breeding and selecting dogs for at least 14 000 years.
The results of this selection are too familiar to need description. All
breeds of dogs are interfertile, but some crosses, for example between a
one-kilogram chihuahua and a great dane weighing seventy-five times as
much, are prevented by the great disparity in size. A cross between a
great dane and a St Bernard results in seriously defective offspring,
but this is not because the parents belong to different species; it is
because each of these breeds has been selected for giant size as far as
it will go, and crossing these two specialized lines of giants results
in partial breakdown of the mechanism of development. In the same way,
bulldogs have been selected for their peculiar characteristics to the
point where many males are infertile.
"We can take the breeds of dog as an indication of the potential
variability inherent in a single species of mammal."
Note the similarity between Patterson's last statement and Marsh's
first.
Mayr [pp133-134]
"Another domestic animal for which claims have been made for a
diphyletic origin is the dog. Its evident ancestor is the wolf (_Canis
lupus_), but there are claims that the jackal (_Canis aureus_) has also
been domesticated and has contributed genes to some dog races,
particularly those of the subtropical and tropical Old World (including
the dingo). This double ancestry of the dog is very doubtful. Indeed
Matthey insists (on the basis of analysis of dog chromosomes) that the
wolf is clearly the exclusive ancestor of the dog. It is probable,
however, that different geographic races of the wolf (particularly
_lupus_ and _pallipes_) have been domesticated independently."
Dobzhansky [p169]
"In domesticated animals and plants the control of reproduction is
exercised by man. Consider the races (breeds) of dogs, many of which
live sympatrically. The gene exchange between them is restricted or
prevented by man. When this restriction is weakened, the once separate
sympatric races fuse into a single variable race - the mongrel."
Thus the differentiation induced by selective breeding is not completely
one-way, and can be undone, at least to some extent.
[pp193-194]
"[T]he longer a species has been domesticated the more numerous and more
diversified are its domestic varieties. Thus the dog is the most
ancient domestic animal, and has produced the largest number of breeds.
Furthermore, some dog breeds differ so much in appearance, as well as in
temperament and behavior, that it is hard to believe that they all
belong to the same species. Compare the little Chihuahua with a Great
Dane, or an ebullient Fox Terrier with a stolid Saint Bernard.
Nevertheless, all these breeds do belong to one species, since they are
capable of exchanging genes, and often do so, either directly by
occasional hybridization, or via the intermediate breeds where crossing
is impossible because of an extreme difference in size."
It may be noted that such differences in morphological characteristics,
were they to be found in the fossil record, would very likely be
classified into several species. One wonders to what extent current
fossil classifications may be erroneous due to this sort of phenomenon.
---
I conclude from such considerations as the above that the dog is not a
very good example of significant evolution and simply represents
intraspecific variation. The facts seem to me rather in line with what
some creationists refer to as "variation within a kind." The dog
represents of course only one example, and the conclusions to be drawn
from it should not be extrapolated lightly. But one may tentatively say
that, as the dog is (or seems to be) one of the most widely given
examples of change in the literature, this conclusion may be valid in at
least a somewhat more widespread sense (e.g., it seems to be extensible
to other domesticated animals).
There are, however, at least two phenomena that give me pause, so that I
would not try to apply this as a universal rule.
(i) Drosophila do reach the point of reproductive isolation. Thus
they qualify as different biological species.
(ii) Polyploidy in plants generates instant (biological) species.
Mike Huybensz has been hitting us creationists on the head with
this one (perhaps he would phrase it a little differently) and
rightly so. Polyploidy results in an instant reproductive
barrier. The polyploid plant cannot reproduce with its parent
stock, though it can reproduce with other plants like itself
quite happily. When one considers that about half of the
300,000 known species of angiosperms (flowering plants) are
polyploids, the significance of the phenomenon becomes clear.
It seems to me that this is certainly something for creationists
to consider. The "kind" would have to be defined very broadly
to account for this (I think - am I wrong?).
I suppose that I should add that I see this as a problem in
regard to the definition of "kind" only, not in the sense that
it must somehow be explained away in order to rule out
evolution. That is not necessary. It is a widespread
phenomenon; however, we may reasonably ask: what does
polyploidy produce? First, observe that its occurrence is much
more common in plants than in animals, where the incidence is
very much lower. One might expect then that if plant evolution
had actually happened in this manner that we would see more
species of plants than animals. In fact the number of species
of animals is much greater than that of plants. So it would
appear not to have played that large a role.
Second, polyploidy does not result in addition of anything new,
it only increases the quantity of what is already present in
existing organisms. So it does not solve the problem of the
evolution of new structures.
---
Finally, I would like to point out for further reference that if
evolutionists wish to use dogs as an example of evolutionary change,
then another claim that has been made (the claim of "only 100 years or
observed artificial selection") goes out the window. It would be more
like, I suppose, 10,000 years or so - 100 times longer! (14,000
according to Patterson). And what do we have after 10,000 years?? Lots
of different dogs, morphologically different, but interfertile. Thus
they are not even biological species (reproductive isolates).
See, e.g., Hitching [p39].
"Nor have these experiments simply happened during the last century or
so. Ever since Neolithic man started crossbreeding wild varieties of
grass, such as einkorn, more than 10,000 years ago, plant domesticaion
can be seen in the archaeological record. Domesticated dogs arrived
about the same time. Yet in the whole of this time period, there is no
hint of wheat or dogs changing into anything except different kinds of
wheat and dogs."
---
References
Theodosius Dobzhansky, _Evolution, Genetics and Man_. John Wiley and Sons, New
York, 1955.
Duane Gish, _Evolution: The Fossils Say No!_. Creation-Life
Publishers, San Diego, 1978.
Richard Goldschmidt, _The Material Basis of Evolution_. Yale University
Press, New Haven, 1940.
Pierre Grasse', _Evolution of Living Organisms: Evidence for a New
Theory of Transformation_. Academic Press, New York, 1977.
Francis Hitching, _The Neck of the Giraffe_. New American Library
(Mentor), New York, 1982.
Frank Lewis Marsh, _Evolution, Creation, and Science_. Review and
Herald Publishing, Washington, DC, 1947.
Ernst Mayr, _Animal Species and Evolution_. Belknap Press, Cambridge,
1963.
Colin Patterson, _Evolution_. British Museum of Natural History,
London, 1978.
--
|
Paul DuBois {allegra,ihnp4,seismo}!uwvax!uwmacc!dubois --+--
|
"The presence of weeds in the garden is not explained by |
saying that the gardener has not pulled them yet."keithd@cadovax.UUCP (Keith Doyle) (05/04/85)
>Finally, I would like to point out for further reference that if >evolutionists wish to use dogs as an example of evolutionary change, >then another claim that has been made (the claim of "only 100 years or >observed artificial selection") goes out the window. It would be more >like, I suppose, 10,000 years or so - 100 times longer! (14,000 >according to Patterson). And what do we have after 10,000 years?? Lots >of different dogs, morphologically different, but interfertile. Thus >they are not even biological species (reproductive isolates). > >-- > | >Paul DuBois {allegra,ihnp4,seismo}!uwvax!uwmacc!dubois --+-- > | Still, that 10,000 years of 'observed artificial selection' you're talking about were not specific attempts to achieve reproductive isolation. You are assuming that people breeding dogs for various characteristics are using the same techniques that one expect would produce such reproductive isolation. I would agree that the domestic dog is probably not a very good example of evolutionary change. At the moment, I would be more inclined to pick the horse/mule combination, or your example of Drosophila. Note that 'observed artificial selection' varies depending on what you're selecting for, and 10,000 years of dog breeding is not what I would consider a particularly good experiment for reproductive isolation. And, I suppose it may also be argued that 10,000 years is still a drop in the evolutionary bucket. (I thought creationists thought the world was less that 10,000 years old anyway?). Keith Doyle # {ucbvax,ihnp4,decvax}!trwrb!cadovax!keithd
beth@sphinx.UChicago.UUCP (beth d. christy) (05/04/85)
Whew, that was a long one. I'm not even gonna try to wade through it all again at 1200 baud trying to find the couple pieces I want, so I hope y'all can trust my memory. I think the dog example is primarily used as an (extremely powerful) example of how changes, once induced, can survive and propogate. It most certainly is not an example of natural selection per se, as it is not a case of a live-or-die, reproduce-or-not response to a new environment. As your first evolutionist example pointed out, it was exactly the opposite. Human's were protecting "degenerate" creatures, and allowing (actually, forcing) them to reproduce. And (important point here), they did it with the goal of *maintaining* most of the qualities of the species (although in some exaggerated form). Natural selection does not offer that protection, and it does *not* have that goal. So if indeed dog-breeding was used as an example of natural selection, you're correct to point out that that's innappropriate. But as an example of the survival/propogation of change, it's pretty irrefutable, and that's important to evolutionary theory too. -- --JB "The giant is awake."
mrh@cybvax0.UUCP (Mike Huybensz) (05/09/85)
In article <1012@uwmacc.UUCP> dubois@uwmacc.UUCP (Paul DuBois) writes: > > In response to some of Ron Kukuk's postings, two or three people have > given the dog as an example of observable evolutionary change. > Certainly they appear to vary widely. In reply, I offer the following. (Many lines of examples deleted to keep me from appearing on the list of biggest posters. :-) > I conclude from such considerations as the above that the dog is not a > very good example of significant evolution and simply represents > intraspecific variation. The facts seem to me rather in line with what > some creationists refer to as "variation within a kind." Of course it does. Because creationists have never said what constitutes a "kind". No matter how large a pattern of variation (or evolution) you present, a creationist can just dismiss it as "a kind". > There are, however, at least two phenomena that give me pause, so that I > would not try to apply this as a universal rule. > > (i) Drosophila do reach the point of reproductive isolation. Thus > they qualify as different biological species. > (ii) Polyploidy in plants generates instant (biological) species. > Mike Huybensz has been hitting us creationists on the head with > this one (perhaps he would phrase it a little differently) and > rightly so. Polyploidy results in an instant reproductive > barrier. The polyploid plant cannot reproduce with its parent > stock, though it can reproduce with other plants like itself > quite happily. When one considers that about half of the > 300,000 known species of angiosperms (flowering plants) are > polyploids, the significance of the phenomenon becomes clear. Thanks for the complement. It warms my heart to see acknowledgement that my points are telling from such a confirmed skeptic of evolution. > It seems to me that this is certainly something for creationists > to consider. The "kind" would have to be defined very broadly > to account for this (I think - am I wrong?). Not at all: the idea of a kind in no way rules out reproductive isolation within a kind. The problem is though, that if one allows reproductive isolation within kinds, you then are not parsimonius in your original assumption of multiple kinds. In other words, the single "kind" that represents all life is more parsimonius than the multiple kinds that creationists claim originated as in Genesis. > I suppose that I should add that I see this as a problem in > regard to the definition of "kind" only, not in the sense that > it must somehow be explained away in order to rule out > evolution. That is not necessary. It is a widespread > phenomenon; however, we may reasonably ask: what does > polyploidy produce? First, observe that its occurrence is much > more common in plants than in animals, where the incidence is > very much lower. One might expect then that if plant evolution > had actually happened in this manner that we would see more > species of plants than animals. In fact the number of species > of animals is much greater than that of plants. So it would > appear not to have played that large a role. Actually, there has been substantial speculation that polyploidy was quite important in the evolution of the higher taxa of the vertebrates. I don't know where it has gone lately: it struck me as rather fanciful. But the question of reproductive isolation from mechanisms other than polyploidy would still be very important to creationists. > Second, polyploidy does not result in addition of anything new, > it only increases the quantity of what is already present in > existing organisms. So it does not solve the problem of the > evolution of new structures. Polyploidy can allow new features. First, by recombination of alleles in ways that were not possible before. Second, by providing working space for variation in extra copies of genes. For example, say there is a vital gene. If it mutates to something that cannot perform the vital function, but is useful in another way, it would be strongly selected against in a normal diploid organism. In a polyploid organism, there would be little or no selection against it: the organism can have a set of two ordinary vital genes and one or more of the mutant gene in the other set of chromosomes. The polyploid organism could have its cake and eat it too. > Finally, I would like to point out for further reference that if > evolutionists wish to use dogs as an example of evolutionary change, > then another claim that has been made (the claim of "only 100 years or > observed artificial selection") goes out the window. It would be more > like, I suppose, 10,000 years or so - 100 times longer! (14,000 > according to Patterson). And what do we have after 10,000 years?? Lots > of different dogs, morphologically different, but interfertile. Thus > they are not even biological species (reproductive isolates). 100 years for fruit flies is approximately 2500 generations. For dogs, 10,000 years is approximately 10,000 generations. The difference is not that great. You also provided examples of non-interfertile varieties of dogs (Great Danes and Saint Bernards.) But that's not germaine to the question of species. Species is a descriptive term: it has no real existence any more than "large" does. Like "large", it varies depending on the context, and like "large" it is a term whose use is a matter of convenience in description. When we talk about species, we want clear boundaries: but they may not exist. Reproductive isolation in nature seems to be common (though not always 100% isolation.) We like to delineate species where reproductive bottlenecks occur and where the character differences are most reliable. Domesticated animals tend not to have reproductive bottlenecks because humans haven't selected for them. There is substantial evidence that natural selection for reproductive bottlenecks does occur. That's why it is usually inappropriate to talk about domesticated varieties being different species, but why it is appropriate to talk about wild species that can be crossed in the laboratory. > See, e.g., Hitching [p39]. > > "Nor have these experiments simply happened during the last century or > so. Ever since Neolithic man started crossbreeding wild varieties of > grass, such as einkorn, more than 10,000 years ago, plant domesticaion > can be seen in the archaeological record. Domesticated dogs arrived > about the same time. Yet in the whole of this time period, there is no > hint of wheat or dogs changing into anything except different kinds of > wheat and dogs." Hitching overlooks quite a number of things here. First, he overlooks maize, which is amazingly different than its ancestor teosinte. Check the recent (past 4 years) article in Scientific American on the origin of corn. Second, wheat is primarily polyploid. Most varieties are tetraploid or hexaploid. Putative wild species are diploid. But mostly, we have a lack of specificity of what kinds are: we might just as well describe humans as a different kind of fish. The creationist idea of a kind includes limits to variation. It is up to them to show the limits: evolution postulates none. -- Mike Huybensz ...decvax!genrad!mit-eddie!cybvax0!mrh
dubois@uwmacc.UUCP (Paul DuBois) (05/10/85)
>> [Paul DuBois] >> In response to some of Ron Kukuk's postings, two or three people have >> given the dog as an example of observable evolutionary change. >> Certainly they appear to vary widely. In reply, I offer the following. >[Mike Huybensz] >(Many lines of examples deleted to keep me from appearing on the list >of biggest posters. :-) Hey! >> There are, however, at least two phenomena that give me pause, so that I >> would not try to apply this as a universal rule. >>... >> (ii) Polyploidy in plants generates instant (biological) species. >> Mike Huybensz has been hitting us creationists on the head with >> this one (perhaps he would phrase it a little differently) and >> rightly so. Polyploidy results in an instant reproductive >> barrier. > Thanks for the complement. It warms my heart to see acknowledgement that > my points are telling from such a confirmed skeptic of evolution. I guess I better knock it off, then! I wouldn't want to appear reasonable or anything. :-) -- | Paul DuBois {allegra,ihnp4,seismo}!uwvax!uwmacc!dubois --+-- | "The presence of weeds in the garden is not explained by | saying that the gardener has not pulled them yet."