Canadian Black Squirrels Take Over Washington D.C.

 
Okay, so "taking over" may be a bit of an exaggeration. But according to the Washington Post black squirrels now make up 5-25% of the squirrel population. They are descended from a small number of Canadian black squirrels released about 100 years ago.

Black squirrels are much more common in Toronto than gray squirrels so there's always been speculation about why that is. So far there's no evidence of a selective advantage so it's probably due to random genetic drift. In fact that's what the result in Washington suggests to me. But that's not what the newspaper article says, ...

Scientists say it's a real-life example of natural selection at work, which has rolled on for a century here without much public notice.

The IDiots have jumped all over this one and for once they may be partly right.


Denyse O'Learly criticizes the article in The Washington Post Thinks It Has Discovered Natural Selection. I agree with Denyse that this is probably not natural selection. It's a clear and wonderful example of evolution—because allele frequencies in the squirrel population are changing—but the mechanism is probably random genetic drift.

I wish people would understand the difference between evolution and natural selection. If you are a pluralist, you recongize several different mechanisms of evolution and natural selection is only one of them. That's why pluralists (i.e. most evolutionary biologists) are not Ultra-Darwinians.

[The photo is borrowed from the definitive website on blackskwerls. Don't go there unless you're prepared to be really, really frightened. The truth about the black squirrel invasion is ....]