Evolution? How?

timberlandko wrote:

real life wrote:
timberlandko wrote:
The likelyhood of natural hybridization is slim at best,

Well, apparently we would both have to come to the conclusion that even if this is true today (by no means an established proposition) , it wasn't necessarily true in the past.
If you take the position that one evolved from the other then there would have had to have been considerable interbreeding for a number of generations, unless you want to postulate that it all took place in one swell foop.

Ignorant, unthinking poppycock. An isolated population is an isolated population, distinct and separated - generally by geologic, climatologic, and/or or other environmental barriers - from populations of like kind. The members of an isolated population breed with one another, not with representatives of the population(s) from which they are isolated. Thats the point of "isolated" - non-contact with others not in like manner and location separated into a distinct, isolated population - the concept is quite simple, really not even requiring much depth of thought to grasp. Apparently, more depth of thought, however, than achieveable by some.

The point, which you apparently missed, was that they weren't always isolated.

You do think that one evolved from the other, don't you?

Don't you think that this means they originally were together?

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worse than that. They were the same friggin species. Whats the point?

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I've come to the conclusion there is no point, apart from the entertainment value therein, trying to put the point across to rl, who pointedly assays to misconstrue any point made, while offering no points in response, thus providing great entertainment. What rl conclusively has demonstrated is a thorough lack of scientific understanding, coupled with a complete divorce from intellectual honesty.

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timberlandko wrote:

I've come to the conclusion there is no point, apart from the entertainment value therein, trying to put the point across to rl, who pointedly assays to misconstrue any point made, while offering no points in response, thus providing great entertainment. What rl conclusively has demonstrated is a thorough lack of scientific understanding, coupled with a complete divorce from intellectual honesty.

Weak dodge, Timber. Why can't you simply admit the obvious, that they interbred for probably quite a long period of time?

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What are you talking about, rl - what interbreeding? An isolated population develops uniquely identifying characteristics because it has no unisolated like kind with which to interbreed; thats what genetic isolation is all about - what part of that don't you get?

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No, they speciate for a long time, A variant emerges that is more successful for a specific environment. That doesnt mean that the other disappears or even keeps breeding with the new form. (doesnt deny it either). As speciation proceeds, morphological and breeding patterns emerge that "isolate" the proto polar bear from its original species. This could have occured in a number of family groups (it could have been genetic drift if the pop was relatively small) .
The morphological changes accompanied the reproductive isolation. The brownies kept boreal and the proto polars wandered more on the ice pack. The bear is stilol evolving. Im not sure of the genetic variation of the entire species but a genomic study could be done to evaluate the foundation species location and its similariies with the foundation population of brownies.

Interbreeding (non isolation ) gets rarer and rarer as subspecies status is attained . Then as full reproductive isolation is established (maybe , in this case, by now , geographic isolation is also an engine of evolution) The emergant population of polar bears fills the empty niche and morphological changes occured rather quickly.

The process of speciation does imply a certain amount of what you call "interbreeding and even inbreeding until a viable population is established" .

After all how do we get a basenji to become a great Dane? or a chihuahua for that matter? some selected interbreeding(and inbreeding) goes on for some time until viable non inbred populations are established. In natural populations , these inbred individuals may not have conferred any vigor, or they may have an advantage

Devining what we can from the fossils of polar bears , the Signor-Lipps effect( a fancy name fior some common sense really) would predict that occurance of fossilized incremental members of a speciating clade are a function of the numbers of speciating individuals. Therefore the original fossil record of the earliest polar bears are only seen when there "are enough of them around in their habitat" .

Theres really no case to be made for or aginst interbreeding. If there were no sex , there would be no little polar bears.

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Behavioral isolation
In other cases they are separated by geographic barriers that effectively prevent any individuals from the two groups from coming in contact with each other. If this geographic isolation lasts long enough, they may become behaviorally or reproductively isolated, or both. Grizzly bears and polar bears are a case in point. Their genetic lineages diverged less than one million years ago according to the evidence of mitochondrial DNA. They have produced viable offspring from matings in zoos; in one case a male polar bear accidentally got into an enclosure with a female Kodiak bear at the U.S. National Zoo in 1936. They mated and had three hybrid offspring. A breeding experiment was then conducted and the hybrid offspring proved able to breed successfully with each other, indicating that these two species of bears were much more closely related than previously expected. In fact all the species in the subfamily Ursinae (all bears except the giant panda and the spectacled bear) probably have the ability to crossbreed, and several combinations have actually occurred.

Polar bears are the closest relatives of brown bears. They must have diverged from an ancestral population of brown bears that became isolated away from the mainland, and other brown bears, about one million years ago. We can imagine that the ancestral polar bears were brown bears that lived in northern Siberia, perhaps along the coast of the Arctic Ocean or on Wrangell Island. They discovered an abundant source of food in the form of marine mammals; seals, walruses, and even whales, and learned to prey upon them. As they were doing this, the group of bears became isolated. It may have been a relatively small group to begin with, and they may even have been stranded on the ice when it receded away from shore during a period of warm climate. We will probably never know the whole story. Somehow, perhaps improbably, they managed to survive and reproduce. Adaptations that favored their new environment would have been rapidly selected for, and they developed white coats and thick layers of fat. In a relatively short period of evolutionary time, they became the polar bears that we know today.
http://www.grizzlybear.org/bearbook/polar_bear.htm

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Thanks, Pauligirl - good info there; sorta what I was trying to get at, but laid out more concisely. Presented with a uniquely exploitable niche, or confronted by a uniquely challenging niche, the critters with the genes that make the grade fill the niche with increasingly successful adaptations of the original critter, which successive adaptations go on to inhabit the niche, breeding truer to the niche-ideal configuration with each generation ... pretty soon, niche-specific sub species.

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Genes dont control speciation environments do. Genes are just Bookkeeping "We must always remember that" 'The genetic variation first begins the process, either as geographic isolates or behavioral " ring species"

I like that summary Pauligirl, very nice, but I want real life to give his contraindications that "interbreeding" doesnt preceed speciation. Hes trying his "one sided equation" logic again and so far weve given him all hes asked for but he may still deny speciation.

OR , he may just take a jump back and say "speciation doesnt confer any new genes, theyre still just bears)

I saw where Craig Venter(cetus ceo) has , in a worldwide cruise searching for genetic diversity, discovered over 10^9 new gene sets usin just oceanic derived planktonic biomass. Hell probably patent new enzymes for product manufacture (like biofuels) and hes also discovering just the smidgeon of new information of genetic variability on the planet.

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timberlandko wrote:

Thanks, Pauligirl - good info there; sorta what I was trying to get at, but laid out more concisely. Presented with a uniquely exploitable niche, or confronted by a uniquely challenging niche, the critters with the genes that make the grade fill the niche with increasingly successful adaptations of the original critter, which successive adaptations go on to inhabit the niche, breeding truer to the niche-ideal configuration with each generation ... pretty soon, niche-specific sub species.

And it's an on-going process...

http://www.search.com/reference/bear
Occasionally, barren-ground grizzlies are found hunting seals on the sea ice north of the Canadian mainland. The barren-ground grizzlies appear to be brown bear/ polar bear crosses, and could represent an intergrade form. Brown bears also occur on three large islands in the gulf of Alaska, and are isolated geographically from very similar coastal brown bears.
------------------------------------
There is also evidence that, unlike their neighbors elsewhere, the brown bears of Alaska's ABC Islands are more closely related to polar bears than they are to other brown bears in the world. Researchers Gerald Shields and Sandra Talbot of the University of Alaska Fairbanks Institute of Arctic Biology studied the DNA of several samples of the species and found that their DNA is different from that of other brown bears. The researchers discovered that their DNA was unique compared to brown bears anywhere else in the world. The discovery has shown that while all other brown bears share a brown bear as their closest relative, those of Alaska's ABC Island's differ and share their closest relation with the polar bear.
http://www.gi.alaska.edu/ScienceForum/ASF13/1314.html

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Pauligirl wrote:

timberlandko wrote:
Thanks, Pauligirl - good info there; sorta what I was trying to get at, but laid out more concisely. Presented with a uniquely exploitable niche, or confronted by a uniquely challenging niche, the critters with the genes that make the grade fill the niche with increasingly successful adaptations of the original critter, which successive adaptations go on to inhabit the niche, breeding truer to the niche-ideal configuration with each generation ... pretty soon, niche-specific sub species.

And it's an on-going process...

http://www.search.com/reference/bear
Occasionally, barren-ground grizzlies are found hunting seals on the sea ice north of the Canadian mainland. The barren-ground grizzlies appear to be brown bear/ polar bear crosses, and could represent an intergrade form...........

Ya don't say! Did they escape from the zoo?

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Now, that's really interesting - seems to indicate at least the possibility some current in-the-wild hybridization. Sorta surprising to me, that; I'd have figured more along the lines of a bear brawl than a bear hug should a Brownie and a Polar encounter one another ... love is strange, though.

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BTW Timber, did you get a polar bear? You got a 50 cal S&W pistola?

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Note, rl, the article offers conjecture, not finding, re hybridization. It is known viable offspring can result, but I'm not at all certain, nor are the article's authors, that in fact in-the-wild hybridization occurs. They merely offer it as a possibilitygiven the apparent evidence. One of those "Stay tuned for further developments" deals of the sort for which science is so famous, and of which ID-iocy is incapable of conceptualizing.

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They see it as a possibility, just as I had. Good to see you coming aboard. Pass the coffee.

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timberlandko wrote:

Note, rl, the article offers conjecture, not finding, re hybridization. It is known viable offspring can result, but I'm not at all certain, nor are the article's authors, that in fact in-the-wild hybridization occurs. They merely offer it as a possibilitygiven the apparent evidence. One of those "Stay tuned for further developments" deals of the sort for which science is so famous, and of which ID-iocy is incapable of conceptualizing.

I thought they were saying that the barren-ground grizzlies came from a brown /polar cross and and are a sub-species at a range boundary.
P

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farmerman wrote:

BTW Timber, did you get a polar bear? You got a 50 cal S&W pistola?

Yeah - it was back in the '70s, near Churchill - as bush-plane hops go - out on Hudson Bay ice. Pretty neat - it was a fly-in, with Inuit guides and dogsleds and all that - tents, though, no igloos. My Polar Bear was a male, about 7 years old, 1020 pounds - big, by my standards, but nothing particularly special to the locals, just a nice bear. The fur is pretty stiff, at least the guard coat, and is sorta translucently whitish-yellowish off-white. Huge claws on the forepaws - really huge paws, too, with webbing between the digits and fully-haired pads. Canine teeth like no other bear - really impressive. A non-resident license was several hundred dollars back then, I understand today its somewhere around $20 Grand or so - outta my league by a good bit, now.

I used a trusty old Remington Model 70, in 30.06, Leupold 3-9x40mm scope, Federal Premium VitalShok High-Energy 180 Grain - prolly about the most versatile North American big-game rifle/scope/ammo rig there is (and, as 2 of the 3 Inuit guides had the same rig - the other had a Remington .300 Mag - I felt reasonably comfortable with it Mr. Green

). The same rig has brought down everything from deer to bison, 300 pound local-grown bears to a 1375 pound Kodiak. The deer and local bear don't call for quite so aggressive ammo, though - I'll go easier on the shoulder any time it makes sense.

Pauligirl - what the article said:

Quote:

The barren-ground grizzlies appear to be brown bear/ polar bear crosses, and could represent an intergrade form ...

"appear to be" and "could represent" - reads like indication as opposed to finding from where I sit. I don't argue that it ain't so - nothing absolutely precludes hybridization, I am just not aware of any conclusive evidence of it. One thing about Mother Nature; if she can, she generally will, so it well could be that they interbreed. As I said, though, I'm not aware of any solidly recorded evidence for same.

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awesome discussion on speciation!

(best series of pages in this thread)

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remember all the speculation and the artices on the isolation mechanism has no evidence or secure data and we werent around to see it. Like the red wolves of the African rift, the isolation mechanism dveloped within a few foundation communities at roughly the same times. They were symaptric in their speciation and sre genetically almost identical.
As rl was trying to infer, the "isolation" mechanism often develops through time and interbreeding occurs during the litle steps that the animals go through before achie.ving genetic isolation. The Hardy Weinberg expansion would predict that, if an expression occurs in a community, it occurs in a fairly predictable level of production. MAybe all the major features that define a polar bear were acquired as a population variation and true isolation wound up at the time when variability of estrus or mate selection made the big jump occur.
From one of those links that pauligirl posted, I thought it said that canid and molar development for "seafood" eating were recent morphological developments, whereas their long neck, "Roman nose" big feet small ears, and unique hollow outer fur were early features that could have been acquired as mere population variations , just like the unimportant genetic differences among dog varieties.

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timberlandko wrote:

Pauligirl - what the article said:

Quote:
The barren-ground grizzlies appear to be brown bear/ polar bear crosses, and could represent an intergrade form ...

"appear to be" and "could represent" - reads like indication as opposed to finding from where I sit. I don't argue that it ain't so - nothing absolutely precludes hybridization, I am just not aware of any conclusive evidence of it. One thing about Mother Nature; if she can, she generally will, so it well could be that they interbreed. As I said, though, I'm not aware of any solidly recorded evidence for same.

I don't think I explained my thought very well. I'm not saying that every barren ground grizzley is a direct cross breed.. ...only that barren-ground grizzlies may be a result of a long-ago hybridization, maybe an overlapping ring species.
Of course there's nothing to back that up...now.
P

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