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Author
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Topic: Support for PEH
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Bruce Fast
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Member # 924
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posted 10. May 2006 12:54
When I read a recent Canadian news article, I could not help but consider that it supports Davison's PEH.
It seems that a grizly/polar bear cross was recently discovered. See Canadian Broadcasting Coporation.
Based upon polar bear evolution the polar bear has been isolated from the other bears for 100,000 to 250,000 years. Yet the "it can mate" species barrier has not been crossed. (Of course we are unable to confirm whether the offspring is firtile.) This would seem to support John Davison's position that isolation alone, even with extensive time separation, will not produce speciation.
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John A. Davison
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posted 11. May 2006 00:26
The primary cause of infertlity in hybrid animals is due to the fact that the chromosomes have been structurally altered to such an extent that they cannot undergo a normal meiosis. All the allelic mutations in the world will not produce hybrid sterility. The acid test would be the cross between a Chihuahua and a Great Dane. While it might require artificial insemination I am convinced it would succeed in producing fertile hybrids in either direction. It will not be done by Darwinians for the same reason they refused to test Darwin's finches, among the
easiest of all birds to domesticate. I don't have to explain why do I?
A fertile hybrid has already been demonstrated to have been produced by a spontaneous cross between a male St Bernard and a female Dachshund.
There are sins of omission as well as of commission.
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John A. Davison
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posted 11. May 2006 00:31
Of course it can be confirmed if the offspring is sterile or not. It is called the experimental method. Where is the cub?
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John A. Davison
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posted 11. May 2006 07:43
Since the presumed hybrid was shot it seems unlikely that we can test it.
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Zachriel
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posted 11. May 2006 12:55
Bruce Fast: "Yet the 'it can mate' species barrier has not been crossed."
Speciation is a process whereby a population will diverge to the point that no significant gene flow between the sub-populations occurs. Once this occurs, then chance and necessity will tend to cause continued divergence.
In many cases, there is no strict dividing line of speciation and the populations in response to environmental conditions may oscillate between divergence and convergence over time. Crosses between different species of bear are certainly possible, but significant gene flow is unlikely due to behavioral and geographic separation, and continued divergence is expected. However, environmental changes could alter this expectation.
John A. Davison: "The acid test would be the cross between a Chihuahua and a Great Dane. While it might require artificial insemination I am convinced it would succeed in producing fertile hybrids in either direction."
Chihuahuas and Great Danes are members of a single species (and most biologists also include wolves). Whether a direct cross is physically possible or not, there is significant gene flow through intermediate breeds.
John A. Davison: "It will not be done by Darwinians for the same reason they refused to test Darwin's finches, among the easiest of all birds to domesticate."
It is already known that most species of Darwin's finches will hybridize. Many plants will hybridize even across different genera. Hybridization is not a secret. It's even in the dictionary.
hybrid: an offspring of two animals or plants of different races, breeds, varieties, species, or genera.
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Scott
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posted 11. May 2006 14:50
quote:
Speciation is a process whereby a population will diverge to the point that no significant gene flow between the sub-populations occurs. Once this occurs, then chance and necessity will tend to cause continued divergence.
Chance and necessity are not causes. More specifically, chance and necessity cannot cause continued divergence.
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Zachriel
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posted 11. May 2006 16:12
Scott: "Chance and necessity are not causes. More specifically, chance and necessity cannot cause continued divergence."
I used broad terms. As chance and necessity can be directly observed affecting populations, I'm not sure what your point is. If you prefer, mutation, natural selection, genetic drift, environmental changes and the vagaries of life, etc.
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Bruce Fast
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Member # 924
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posted 11. May 2006 17:52
Zachriel, the John Davison, in his PEH and elsewhere, has suggested that speciation no longer occurs, that evolution is no longer observed. However, though the definition of the term "species" doesn't seem to be terribly consistent, within the context of the PEH, "species" is clearly defined as a group of creatures who can mate to produce fertile offspring. It seems therefore that if one is discussing the PEH, as this thread is, one must use this narrow definition of species.
(My understanding is that this was the original definition of species, but that a broader "creatures who do not 'normally' mate" has become commonplace. My sense is that the latter is the case to allow more scientists the privelage of naming a species. Further, I guess, not having to attempt mating of various creatures to establish whether one has found a new species is an advantage of this definition.)
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DaveScot
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posted 11. May 2006 20:06
Bruce,
The biological definition of species has been all but abandoned in practice because it's impossibly difficult to test in most cases. It's often exceedingly difficult to get two members known to be the same species to mate in captivity. How much more difficult to get two critters to mate that might not even be the same species! Compounding the problem is that hybrid infertility isn't a can/cannot proposition. It's more of likely/unlikely situation. For instance there are several reports of fertile mules which were once thought to be quite infertile. As it turns out they're not totally infertile but almost infertile.
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Bruce Fast
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Member # 924
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posted 12. May 2006 00:26
DaveScot, I went on a little hunt to find what I could find about hybrid breads. I found this website. It is intriguing that the mateability test has a fuzzy edge. It also looks like the wolf, coyote, and jackel are all interbreedable. (I particularly found the successful mating of sheep and goats to be interesting especially in light of their different chromosome counts.)
I wonder, I suggest that the evidence that polars and grizzlies are "biological species" though they have been separated for 250K years. By the same token, does the fuzzy boundary between species challenge the PEH?
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John A. Davison
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posted 12. May 2006 03:02
The definition of species has never been vague and never difficult to determine experimentally. Dobzhansky defined species very simply and unambiguously. Assuming of course that the hybrid can be produced, if the hybrid is fertile the parental forms are the same species. If the hybrid is sterile they are different species. There is nothing vague or unambiguous about this physiological definition. The mule is sterile because its parents were different species. It explains in clear terms what the word species really means. It needs only to be experimentally tested and, when it has been, has never yielded unclear results. Biology is, after all, an experimental science although many aren't always anxious to practice it as such. Apparently it is more fun to engage in idle speculation than in experimental science.
Theodosius Dobzhansky is an interesting character in evolutionary science. Not only did he present a valid, testable definition for species, he also demonstrated beyond any doubt that Drosophila melanogaster was incapable of speciation through the most intensive of selection. Oddly, he remained a devout Darwinian nevertheless.
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Bruce Fast
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Member # 924
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posted 12. May 2006 12:12
Thanks for the comments John. I have two puzzles for you.
1, it was reported earlier in this thread, and I have heard so elsewhere, that not all mules are sterile. If so, there still is something less than perfect about the divide between the species.
2. I seem to remember another reported fruit-fly experiment where the scientist claimed to have produced two separate species of fruit-fly. Now I recall that his test for "species" was that the "oriented to the dark" fruit flies and the "oriented to the light" fruit flies chose not to mate. Certainly this racism on the part of fruit-flies is not the same level of species separation that is being used here. I remember your response was that just because they chose not to mate, that didn't mean they were incapable of mating. (We certainly see it as an oddity when a polar bear and a grizzly mate.) I also, however, don't remember you responding with Theodosius Dobzhansky's findings. Too bad, I was way over my head in a debate with a biologist of the evolutionary school at the time, and would love to have pulled out Dobzhansky and his work.
I have looked into Dobzhansky lightly on google. He is the father of the famous "nothing in biology makes sense except in light of evololution" statement. He seems to have spent a lot of energy opposing the young earth crowd. I have not, however, found any information on his fruit-fly studies. Do you know of any reasonably accessible (ideally summary) material about his work? Further, I wonder if his biological committment is more to the universal common ancestor than it is to the RM+NS mechanism. Would Dobzhansky have potentially understood and respeced your PEH hypothesis if he had the opportunity or was he committed to the RM+NS mechanism?
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DaveScot
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posted 12. May 2006 12:26
There are approximately 1 million documented, ostensible biological "species". How many of those species do you suppose have been cross-bred to see if they can produce a hybrid and of those where breeding was successful how many of those hybrids were mated to determine if they were fertile hybrids and how many pairs of each hybrid type were mated to ensure they were truly sterile and not just reduced fecundity.
As almost anyone should be able to see the number of permutations between closely related species that would need to undergo testing is mind boggling and the effort to insure that each combination is tested thoroughly enough to insure it's a matter of sterility and not reduced fecundity is enormous, especially in organisms that take a long time to reach sexual maturity. Even for fast breeders like insects (7-year locusts and the like excepted) can you imagine how difficult it would be? Many wild organisms can't even be kept alive in captivity to say nothing of testing each one against all other species of its genus or even family for the ability to produce fertile hybrids.
It is for EXACTLY these reasons that the vast, overwhelming majority of specie demarcations are accomplished using comparative anatomy (including today at the molecular scale) and/or reproductive isolation rather than laborious, expensive, time consuming breeding experiments that in any case can't be positive for sterility (it can be positive for fertility only).
According to wikipedi there have been 60 documented cases of fertile mules. A horse has 64 chromosomes, a donkey 62, and a mule 63. It is presumed that the different number and structure of chromosomes causes sterility but in fact it does not or there would be no documented cases of fertile mules. The different number and structure of chromosomes results in reduced fecundity. Also interesting is that mules are less fecund than hinnies and mule mares can be fertile while there is no documented case ever for a fertile mule stallion.
At any rate, the point is that hybrid sterility is a misnomer and a different number of chromosomes results in some level of reduced fecundity but doesn't automatically make a fertile cross impossible.
[ 12. May 2006, 14:52: Message edited by: DaveScot ]
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DaveScot
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posted 12. May 2006 12:56
JAD
quote:
The acid test would be the cross between a Chihuahua and a Great Dane. While it might require artificial insemination I am convinced it would succeed in producing fertile hybrids in either direction.
This is how Darwinists perform science. They imagine how something might work and without experimental verification they convince themselves it does work that way and henceforward act like it has been demonstrated when in fact it remains imaginary.
Speaking of being convinced without experimental evidence, can someone here describe for me what it would take to acquire amphibians heterozygous for one or more chromosome reorganizations so that the basis of the PEH, semi-meiosis, can be tested? Davison is refusing to answer because, I guess, he doesn't like me or doesn't think a published computer hardware/software design engineer with a patent portfolio and long history of fruitful invention in the field is good enough to ask. Surely someone else here must know enough about the subject to describe the labwork required. I'm looking for what test equipment is required, the cost, the number of animals that would need to be screened, and stuff like that. Pretend you wanted a grant to pursue this line of research. What would the grant proposal request in the way of resources?
Or is no one interested in actually determining if there's any merit in Davison's PEH and would rather keep it all a matter of fantasy so we can do what the Darwinists do and convince ourselves that imagining something works is as good as demonstrating it.
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