One can't have a science article, it seems, without the "obligatory" propaganda about global warming.
So we've a sudden appereance of a type followed by such tiny amounts of change that it is impossible for the scientits to tell whether modern voles are a new species, or just a subtype of the voles of 1 million years ago.
This rate of change is woefully inadequate to explain the fossil record. There have probably been over one million new FAMILIES of creatures appear since the first wave of animals arrived in the Cambrian Explosion. That is one new FAMILY every 435 years. This article is another example of my contention that evolution, to the extent it happens, does not happen fast enough or cause change enough to explain the fossil record.
Please note that this species, as well as 99.9% of other extinct species, disappeared without any influence of the National Rifle Association, urbanization, pollution, etc.
It is natural for species to die out and our attempts to prolong this process through environmental impact reports and other such nonsense only serves to breed a larger and more well-funded set of bureaucrats (evolution in action) who impose increasingly onerous regulation on the rest of the population.
However, a major climate alteration about 800,000 years ago dramatically shifted the population balance toward the evolving vole and away from the original vole population.
The original vole population still took about 800,000 years to die out, because it lived as recently as 9,500 years ago. Sediments of that age in a Nevada cave still contain the animals' fossilized teeth. In the last 10,000 years, however, the original vole has disappeared entirely, leaving the new variant that continues to evolve away from the original.
This science writer doesn't seem to have a very good idea of how evolution works. The two populations of voles will evolve at roughly the same rate; it's not true that one population will evolve while the other remains the same. At any given moment, the two populations will be (approximately) genetically equidistant from their last common ancestor.
What they mean is that one population specialized in such a way that their teeth became mophologically different from the parent stock, while the other population's teeth looked about the same as those of the parent stock.
Stylistic complaint: why "however?"
I have some problems with the scenario that the packrats kept returning to this cave, which was only "periodically open" during that period.