Lecture: Polar bears: Narrator: Listen to part of a lecture in a biology class. Professor: Polar bears inhabit the Arctic, on the outer perimeters of the sea, to be exact. When polar bear die, their bones almost always end up deep down on the floor of the icy Arctic Ocean. They basically disappear forever. Recently, however, a polar bear's jawbone was found within the Arctic Circle, on an island in Noway Svalbard archipelago. This bone held in a valuable information regarding the polar bear's revolutionary past. For instance, exactly how long the polar bear has existed as a species has been a matter of wild debate. So researchers took the opportunity to perform dating analyses on the bone, and also to analyze its DNA. The bone was determined to be about 120,000 years old, and the DNA analysis established that it was indeed the bone of a polar bear. Now, in order to map out the polar bear's genetic profile, researchers performed mitochondrial DNA analysis. Usually when we think of DNA, we think of the DNA that's in cell's nucleus, but in fact, a cell mitochondria also contain DNA. In this particular situation, mitochondrial DNA analysis made more sense than nuclear DNA analysis. You remember from a previous lecture that a mitochondrion is the energy producing structure in cells, right? Well, it has a much more stable structure than a nucleus. That's a distinct advantage when you're investigating ancient delicate samples. Additionally, there're up to 1,000 mitochondria within a single cell. But there are only two copies of nuclear DNA within a cell. This abundance of samples makes mitochondrial DNA analysis a much easier procedure. As far as genetics and ancestry are concerned, we've long been aware that polar bears are young species, evolutionarily speaking, and that they branched off from brown bears. But this jawbone fossil has helped us better estimate when that splitting off probably occurred. By the way, as part of their investigation, researchers, studied a unique geographically isolated group of modern brown bears living in southeastern Alaska. It turns out these brown bears have genes that resembled polar bear genes more than they resembled the genes of other brown bears. Anyway, the jawbone fossil appears to have come from a polar bear that had lived shortly after. Well, historically speaking that is, shortly after polar bears agreed to split info a different species. And what does all this mean? Well, because the fossil is so old, polar bears must have survived Earth's last interglacial warming period, about 45,000 years ago. But polar bears are Arctic animals and live on the ice. In that unique environment, how exactly did they manage? Well, one theory suggests that polar bears may have been able to find a few remote cold icy places, such as, well, Svalbard islands to live on until the climate eventually cooled again. Controversially, because the last warming period was actually warmer than the one now, the one more presently experiencing. Some people believe that polar bears will be able to pull through again. But there's something they are not taking into account, namely, the pace at which climate change is occurring today. The climate today is becoming warmer at a very accelerated rate. Polar bears are highly specialized species. It is unrealistic to expect them to be able to adapt in such a short window of time, incidentally, the climate isn't the only factor that might have an effect on the polar bear's future. Recently the offspring of a polar bear and a grizzly bear was discovered in the southern Arctic. This hybrid was a result of a polar bear and a grizzly bear mating. You see it seems that grizzly bears in Canada have been moving northward, intruding on the polar bear's territory. This is actually the first time that we've seen such a hybrid in the wild, but it's possible that hybridization could occur more and more frequently, resulting in increasing numbers of offspring that can no longer be considered true polar bears. And if that pattern continued over time, well ...