Wednesday, April 25, 2012

On The Origin of Polar Bears

Polar bears are cuddly, for some value of cuddly. You wouldn’t actually want to cuddle one, because they stink of fish oil and would tear you limb from limb before you even had time to pinch your nose and say ‘eeeuuugh’, but they are undoubtedly popular, somewhere between puppies and hamsters, I think. They are majestic, beautiful, elegant and brutal. If they could drive sports cars you would have to forbid your daughter to marry one, and she would do it anyway.

They are also endangered, for some value of endangered, and thus they punch even more buttons. They have been used to sell both insurance and refreshing mints, which few people can claim, and can eat baby dolphins with impunity, in which they are surely unique.

But little was known about their origin until very recently, and even that turns out to be wrong. Morphology was all we had until the last couple of decades, and morphology suggested that they were closely related to the brown bear of North America, Asia and Europe. Morphology turned out to be right, as it usually is when closely observed, and analysis of mitochondrial DNA put the separation at only 150,000 ya. This turned out, a posterior, to explain a lot of things.

So it was rather unfortunate when a recent analysis of nuclearDNA showed that the separation was more like 600,000 ya. And it probably was a complete and sudden separation, a small population isolated on floating ice or some such thing. This will also turn out to explain a lot of things, and the explanations may well have started already.

The fact that values for time and (genetic) distance of separation of populations provided by mtDNA and nDNA or aDNA can differ widely is becoming more and more important. Something similar happened with the Neanderthal sequences, and doubtless with sequences of other animals, too. At a time when knowledge of human history is being rapidly expanded by genetic analysis, it is necessary to recognise that no one advance is likely to be definitive, and it will take years of looking at many such data in the context of each other and more broadly, before the kind of detailed understanding we aspire to can be achieved.

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