Now
we know that present conditions have existed in the Arctic for a good
four millions of years. Prior to that, the lack of enough land made
ice cap development and the sequestering of sea ice difficult.
Present conditions are the geological anomaly.
Our
own conditions which are recent and is known as the Holocene is a
direct result of the Pleistocene Nonconformity which settled us with
a remarkably fortuitous reconfiguration of conditions that eliminated
the Northern Ice Age. It is my contention that it is deliberate or
alternatively so remarkably impossible that it is unnatural. I will
not grind the arguments out today but searching this blog will get it
for you.
This
also implies that the Pleistocene menagerie also emerged around the
same time. It also implies that all such creatures are still closely
related to present species as to allow plausible recovery through DNA
recovery and cloning. This will include the short faced bear, the
dire wolf, the giant beaver, the mega lion, the giant elk and many
others. They are already tackling the mammoth.
How Brown and Polar
Bears Split Up, but Continued Coupling
A new study extends
the origin of polar bears back to 5 million years instead of 600,000.
By JAMES GORMAN
For many years,
scientists who study the history of life on earth had to make do with
fossils.
That worked out well
enough for some species that left bones to be buried in river
sediment, or impressions in mud that turned to stone.
But other creatures,
like polar bears, live in more ephemeral environments. When you spend
your days on floes of Arctic Sea ice, death usually means burial at
sea and skeletons lost to time.
The few polar bear
fossils found on land, where they spend much less time, are
scattered, accidental discoveries.
As a result, a good
look at the history of polar bear evolution has had to wait for
investigations of the DNA of living animals. Comparing the DNA of
different but related species can work as a kind of microscope to
look at events as the species separated — events that are otherwise
lost in deep time.
Recently, with studies
of whole genomes, the magnification on the microscope has been
increasing and greater detail has emerged. On Monday a new
report in Proceedings of the National Academy of Sciences pushed
back the origin of polar bears about four and a half million years.
The last
estimate, published in April in Science, put it at 600,000 years
ago, and the new study has it at five million. It reinforces the
previous conclusion that polar bears are not a recent spinoff of
brown bears, and it paints a more detailed picture of what the bears
have been doing all this time as they evolved into the charismatic
megafauna we now use to sell soft drinks and promote
environmental causes.
It has been a busy
couple of years for studies of polar bear evolution. In 2010, a
mitochondrial DNA study of modern bears suggested that the polar
bears might have been a recent offshoot of brown bears, perhaps only
130,000 years old. But mitochondria are little energy factories
passed down in the mother’s egg, and they tell the story of the
female line only.
The study that pushed
back polar bears’ origin to about 600,000 years ago was based on
snippets of nuclear DNA, which comes from both sexes.
But those snippets
represented only selected bits; the new study, by Webb Miller and
Stephan C. Schuster of Penn State, Charlotte Lindqvist of the
University at Buffalo, and an international team of 23 other
scientists, looked at the full genomes of polar bears, brown bears
and black bears. Dr. Lindqvist, the senior author, said the
full-genome approach enabled the scientists to look at polar bear
history in new depth. She was also the first author of the
mitochondrial DNA study.
The progress of
species formation, at least in this case, is a bit like a long,
ambivalent divorce in which the two parties separate but occasionally
fall back into bed even after the official decree.
Dr. Lindqvist, said
the DNA showed evidence of intermittent interbreeding between brown
and polar bears from the time of the split until the present — most
likely during periods of warming, when brown bears moved north and
polar bears were forced onto land.
In most brown bears
the percentage of genetic material traceable to polar bears is 2
percent. But on the Alexander Archipelago, a 300-mile-long string of
islands off the southeast coast of Alaska, the brown bears have 5 to
10 percent polar bear DNA, suggesting more frequent interbreeding.
The microscope of
whole-genome studies and comparisons also gives glimpses into the
adaptation of polar bears to the Arctic environment, including genes
for high fat content in milk and for blubber accumulation.
The report, of course,
offers new material for arguments about what will happen to the bears
as the planet warms. On the one hand, if they’ve been around so
long and have survived many episodes of warming, you could say they
ought to be used to it by now. On the other hand, you could point out
that all those warming episodes were bottlenecks in evolution that
led to a current species with much less diversity than brown bears,
so the current species is ill prepared for a new shock.
And the current
warming is happening much faster than any previous episodes.
One thing the evidence
does suggest, however, is that there may be more interbreeding ahead.
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