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Biology 101: Black squirrels do not exist, except in my backyard
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The lesson started with a single, solitary, nut-hunting, tail-twitching somewhat adorable squirrel. At least I believed him (or her, as the case may be) to be a lone squirrel. I guess it could have been two, or even three (boy or girl) squirrels, as they tend to look alike to the untrained eye - under normal circumstances. For me, normal circumstances - in regard to squirrels - always included one hue. The squirrels frolicking in any neighborhood I've ever lived in have been, decidedly, gray.

Other than occasionally slamming on the brakes in order to avoid hitting one of the road-crossing rodents, I never gave squirrels much thought. Oh, sure, I thought they were cute, with their bushy tails, big dark eyes and the way they held an acorn, just so, with their two front paws. But, other than me throwing them a peanut every now and again, or them scolding me for getting too close to the tree holding their nest, the squirrels went their way, and I went mine.

Until a couple of summers ago, when one squirrel stood out from the local crowd. The creature in question did not possess gray fur or a gray tail. There wasn't a single gray hair on his body. He was, decidedly, black. I regarded his coloration as an anomaly - unexpected, unexplained and not likely to repeat itself.

I was wrong about that last part.

Blackie was the lone black squirrel in my yard two summers ago. Last year a few non-gray family members joined him. Currently, the scope of his presence is visible throughout my neighborhood and town. Seems Blackie (and his offspring) have been fruitfully multiplying.

These observations piqued my curiosity and got me thinking squirrelly thoughts - about fur color, dominant genes, words like heterozygous and other biology topics too numerous to mention. This compelled me to complete a little research on our friend, the black squirrel.

My first discovery was jaw-dropping. There is no such thing as a black squirrel. You read the truth here first. Little Blackie was not a black squirrel at all; he was a gray squirrel - in disguise.

In scientific terms (which I tend to use on a regular basis) black fur on a gray squirrel is brought on by a characteristic known as melanism, which means a darkening of body tissues - including fur and skin. Melanism is the opposite of albinism, where an animal has no pigment and appears white. Melanism is a naturally occurring phenomenon and should not be confused with Photoshopism, which can be duplicated on practically any computer in any kitchen in the country - as long as you've got the software.

I learned, further, black squirrels are rare. Some biologists estimate that in the United States, only one of every 10,000 gray squirrels appears black. Tell that to the scampering rodents living in my backyard - where black is definitely the new gray. (But never, ever shades of it. At least not in this column.)

Rare or not, Internet research made it clear: Black squirrels proliferate because of one main reason - natural selection. It's that simple. If the environment is more conducive to black (over gray) squirrels, they are more likely to survive and reproduce and create baby black squirrels and so on and so on.

One popular and rather logical hypothesis surmised black fur is beneficial in colder climates because it readily absorbs heat, making it easier for squirrels with darker fur to stay warm during a long, cold winter. While this makes sense, I wonder, why now? I've lived in a cold, harsh climate for more decades than I'd like to admit and have yet to hear rumors of global cooling. The weather patterns haven't changed much in my years on this earth, yet the squirrels are just now making the adaptation from gray to black in my neighborhood.

What took them so long?

In my search for answers, the questions - much like the black squirrels in my backyard - kept multiplying. Until I stumbled on the real truth of the matter. Maybe the answer wasn't so much scientific as philosophical.

We can turn to biology for answers. We can dive into research. We can study statistics and try to fit all the pieces of the DNA puzzle together. At the end of the day, though, we are left with a black squirrel that knew nothing about natural selection or the odds of being a melanistic anomaly in a gray-squirrel world. He only knew about the safety of a home in the trees, gathering enough acorns and berries to carry him through the winter and perhaps, if he was lucky, finding a wife to keep him warm during the coldest months. So that's what he did.

Along the way, he was fruitful and multiplied. And he wound up making a difference - on the landscape and to squirrels everywhere (or at least in my backyard). He didn't set out to change his world. He just did.

Best of all, he looked cute while doing it.

- Jill Pertler's column appears every Thursday in the Times. She can be reached at