I was watching David Attenborough's excellent "Frozen Planet" and a post programme discussion in which he said that if warming continued unabated the Polar bear would be extinct.
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| Polar Bear |
Now on the face of it that makes sense but there are a couple of nagging questions that always bug me about this.
According to both fossil and DNA evidence, the polar bear (Ursus Maritimus) diverged from the brown bear (Ursus Arctos), roughly 150,000 years ago and the oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone. However when they evolved, during what geologists describe as the Pleistocene or Ice Age, the ice sheets were more or less permanent from Canada and Russia through to the North Pole. In fact over the vast time span of the Pleistocene (from 2,000,000 - 12,000 B.C), large glacial ice sheets covered much of North America, Europe, and Asia for extended periods of time.
But since the start of the current geological period about 12,000 BC (known as the Holocene epoch), the retreat of the glacial ice has been more or less continuous. So the polar bear has had at least 14,000 years to adapt to the gradual but constant changes caused by warming and ice retreat. Even during the Ice Age the extent of the glacier ice cover was not static, and there were periods when the glaciers retreated (known as the interglacial), because of warmer temperatures, and advanced because of colder temperatures (glacial).
The last ice cover peakage is known as the Last Glacial Maximum (LGM) approximately 20,000 years ago, when the north and south of the planets saw vast ice sheets for the last time.
But there were periods in that two million year epoch when the ice retreat during an interglacial would have been at least the equivalent of the current retreat. So why were polar bears not wiped out the first time the ice broke up and left open sea between the the north pole ice pack and the land?
I have no idea if this is a valid question or not, but I always suspect that someone should be able to answer this before saying that they will be made extinct this time round, when they have so obviously not done so on other occasions ..... maybe the answer to where the polar bears go when conditions no longer suit their lifestyles, lies in a hybrid between grizzly and polar bears? These hybrids, some times called a pizzly bear or prizzly bear, or grolar bear would have all the DNA and characteristics to quickly evolve back into polar bear types when and if the ice cover ever came back.
Its just an idle bit of speculation on one of those imponderables we come across in our lives .... I was just diverted by the notion, and now you have been as well.
But since the start of the current geological period about 12,000 BC (known as the Holocene epoch), the retreat of the glacial ice has been more or less continuous. So the polar bear has had at least 14,000 years to adapt to the gradual but constant changes caused by warming and ice retreat. Even during the Ice Age the extent of the glacier ice cover was not static, and there were periods when the glaciers retreated (known as the interglacial), because of warmer temperatures, and advanced because of colder temperatures (glacial).
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| Climatic indicators for the last 400,000 years. |
The last ice cover peakage is known as the Last Glacial Maximum (LGM) approximately 20,000 years ago, when the north and south of the planets saw vast ice sheets for the last time.
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| Earth At The Last Glacial Maximum |
But there were periods in that two million year epoch when the ice retreat during an interglacial would have been at least the equivalent of the current retreat. So why were polar bears not wiped out the first time the ice broke up and left open sea between the the north pole ice pack and the land?
I have no idea if this is a valid question or not, but I always suspect that someone should be able to answer this before saying that they will be made extinct this time round, when they have so obviously not done so on other occasions ..... maybe the answer to where the polar bears go when conditions no longer suit their lifestyles, lies in a hybrid between grizzly and polar bears? These hybrids, some times called a pizzly bear or prizzly bear, or grolar bear would have all the DNA and characteristics to quickly evolve back into polar bear types when and if the ice cover ever came back.
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| A Female Hybrid, Male Hybrid, Brown Bear And Polar Bear |
Its just an idle bit of speculation on one of those imponderables we come across in our lives .... I was just diverted by the notion, and now you have been as well.
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