I was going to do a post on this study, but this one is far better than anything I could do. The most important thing is never to trust studies that posit a phylogeny or evolutionary history based solely on mtDNA.
Biology Lesson: DO NOT MAKE EVOLUTIONARY TREES OF ANIMALS AND PLANTS BASED ENTIRELY ON MITOCHONDRIAL DNA (mtDNA): PLEASE USE NUCLEAR DNA WHENEVER YOU CAN. THIS IS BECAUSE mtDNA APPEARS TO MOVE MORE READILY BETWEEN SPECIES THAN DOES NUCLEAR DNA (nDNA), CAUSING A DISCORDANCE BETWEEN EVOLUTIONARY TREES BASED ON MITOCHONDRIAL GENES (‘GENE TREES’) AND THOSE BASED ON POPULATION AND SPECIES HISTORY THAT ARE DISCERNED FROM ANALYSES OF MANY NUCLEAR GENES (‘SPECIES TREES’).
I have put that in capslock because I’ve been emphasizing this problem for a long time, and yet many systematists and evolutionary geneticists still persist in using the DNA from mitochondria (the energy-producing organelles in cells that stem from ancient bacteria and have their own DNA) to make evolutionary trees of organisms and estimate their divergence times. They do this because 1) mtDNA is much easier to purify and sequence than is DNA from the nucleus (“nuclear DNA”, or…
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This study also means that polar bears have survived warming periods before, which also means that they aren’t as doomed as a species as was initially believed. Polar bears are not entirely dependent upon instinct, and they could learn to adapt to living a different lifestyle.
my guess is that hybrids are more common in nature than we think. Given that in many, if not all such cases, it’s the females that are fertile, passing on the mother’s MTDNA is far more likely than passing on the sire’s. Probably the same reason why Neanderthal MTDNA didn’t show up in earlier genetic studies (It was far more likely that a Neanderthal male mated with with a human female and the result integrated into human culture than that somehow a Neanderthal female was brought into a H. Sapiens encampment and thereafter had children). But it also makes some of the assertions on canines suspect — the MTDNA may reflect far more recent wolf /dog breedings (such as the W6/D6 clade) than the actual time when wolves/dogs seperated. For that matter, it may be that wolves and dogs have a common ancestor (now extinct), rather than one specific existing wolf subspecies being responsible. With horses and cattle, the original “wild” ancestor is no longer available. It’s very possible, given the huge climate changes of the period (such as the Sahara having once been grasslands) that a subspecies closely related to the Asiatic wolf was the origin of dogs and that the wild relatives developed into what we now know as the Asiatic wolf.
The polar bear is one of those specialist animals that is adapted for a very restricted environment. Such animals are always very vulnerable to climatic or environmental changes (man made or otherwise).
Thanks for posting. Interesting article.
I tend to agree with Peggy’s asumption that the female was more likely to have been one of our lot, ie of the more advanced species and the one which survived, especially given that if it were the other way round we might not be discussing the issue.
We almost know that the neanderthals must have eventually become desperate as the animals they hunted and used for clothing and shelter began to disappear with the onset of global warming. So it’s tempting to speculate that any mixed offspring would have survived better within the more succesful and adaptable homo sapien culture. (It is yet to shown how ‘adaptable’ we remain after the bankers have finished with us!)
Not quite an exact analogy, but it was found in aviculture that when say a goldfinch or related species was caged with a canary, the only babies successfully reared were those from the mating involving a domesticated hen canary, seldom if ever when the hen was a from the wild species. Usually the babies were themselves infertile and were described within the hobby as ‘mules’. However it was eventually discovered that the mating between male south american hooded siskins and hen canaries resulted in some of the offspring being fertile and ultimately this is how the red canary came into being, which today is mainly comprised of canary genes except for those responsible for red feather coloration.
So, finally, if the canary analogy translates to how we north european descended folk are comprised today, I wonder which bits of us might have come from the boyfriend our way back granny never took home? (presumably)