"When faced with several possible explanations of an event, select the one that requires the fewest unprovable assumptions." William of Ockham, 1287-1347
"Evolution is how Life commutes its own death sentence." …Anonymous
(7/2016) It was about this time, four or five years ago, that three black squirrels appeared at our bird feeder. They acted like teenagers, so I assumed that they were born that spring and had recently left the nest and gone out into the world to seek their fortunes, as Grandma taught me animals do.
I knew that they were not new mutants; the gene for blackness is recessive, and is known to be scattered among squirrel populations. If two gray individuals who each have one black gene happen to mate, there is one chance in four that they will have a black pup. Consequently, black squirrels show up here and there, now and then, like Harvey, the pooka who appeared to Elwood
P. Dowd in the form of a 6-foot tall rabbit. But so far, no one has found that black squirrels have any evolutionary advantage in nature; they continue to occur, but do not become abundant. So I accepted the new squirrels and they became part of the family. A few of them are still around.
One morning last week I noticed that a new generation of squirrels had been produced in the Great Forest behind our house, and they had discovered the feeder. At first glance they all looked like normal young gray squirrels, cavorting around as all teenagers do, seeing how fast they could go, how far they could jump, and who dared to go out farthest on
the thinnest branches. However, when one of them stopped to look for sunflower seeds on the ground, I noticed that its tail was different; instead of being uniformly colored, it had light and dark rings. My imagination being what it is, the first thought that came to mind was that the squirrel’s mother might have been frightened by a raccoon. I enjoyed thinking about that for
a few minutes; my grandmother actually believed such things happened, and it had all sorts of possibilities as a topic for story-telling. However, rationality soon returned, and I was forced to fall back on the logic of Ockham’s Razor: "when faced with several possible explanations, try the simplest one first." If the ringed tail was caused by a mutation, that raises three
possibilities. First, this squirrel may be eaten by a predator before it ever reproduces; then the gene would be gone forever. Second, the squirrel may live long enough to reproduce, but remain rare, like the black ones. Third, maybe having a ringed tail will be an advantage, and in a few hundred years all squirrels will have ringed tails. Evolution would have happened, right
here in Emmitsburg!
When I entered the first grade in 1939, the word "evolution" was not used in any of my textbooks. Grades 1 – 6 were all in the same room, and Science was not taught until the third grade; so instead of reading the adventures of Dick and Jane in my own class, I listened to the science lessons of the older kids. I was fascinated to hear that fossils
existed. I had a pony, and one of the lessons said that ponies and horses had a fossil ancestor called Eohippus, which lived millions of years ago. Eohippus was "the size of a small dog," and there were other fossils that followed it; but care was taken in the textbook to avoid the term, "evolution." As I proceeded through the first eight grades, phrases like "ancestor of" or
"descended from" occasionally slipped past the textbook editors, but evolution was never specifically mentioned. My High School biology textbook had a chapter on evolution, and I read it and found it interesting; but the course was taught by the football coach, a nice man who never quite got to that chapter. So the seed was planted. And finally, in college I had an excellent
biology professor who taught about evolution in the introductory course and made it the basis for other courses such as anatomy and genetics; and in graduate school I found it was the basis for understanding ecology.
Looking at the young squirrels cavorting around, it was hard to see how a tail with light and dark rings might be an evolutionary advantage… but maybe that was just because I don’t think like a squirrel. If you’d ask my wife, she would say I do; but that raises the question of whether squirrels think at all. Much of their behavior is the result of
instinct. They don’t have to learn to bury acorns in the fall; they just do it, as a result of neural connections in their brains. Those neural connections have been inherited from generations of ancestors whose survival depended on burying acorns (that’s a sneaky way of saying they evolved). It is logical to think squirrels survive better as a result of burying acorns, but
it’s hard to imagine how having a ringed tail would have anything to do with it.
By that time I was getting a bit frustrated, so I resorted to Wozniak’s Theorem: when all else fails, check the Internet. As usual, it told me a lot more than I really wanted to know. I found animals with ringed tails are wide-spread around the world; in addition to raccoons, there are Civet cats and Coati-mundis in the western U. S., lemurs in
Madagascar, Mongooses in India, Genets and Ring-tailed Possums in South America, Ring-tailed Cats in Africa… everything from marsupials to primates. But there was no explanation of how ringed tails might be an advantage, and there was no mention of ring-tailed squirrels. I was getting desperate.
As a last resort, I went out to the garden and started pulling weeds. There was no shortage of them, and I always find that pulling them out of the ground has a wonderfully cleansing effect on my mind. And it worked again. After an hour or so I had sweated all of the irrelevant and impure thoughts out of my brain, and the answer appeared before me in
little balloons above my head, just as they do to Charley Brown or his dog, Snoopy. And it was so simple!
Maybe the young ring-tailed squirrel is the result of a new mutation that has never happened before in the history of the world. Male squirrels are known to attract females by waving their tails back and forth, and maybe all of the local females will find the ringed tail irresistible. Maybe this male will attract more wives than any other male in the
area, and he will produce more offspring than anyone else in the entire squirrel kingdom! And maybe the mutant gene that caused the rings will be dominant, and before long all of the squirrels in Emmitsburg will have ringed tails! Emmitsburg will be famous. Maybe scholars and experts will come from all over the world to study the new species; maybe they will name it Sciurus
meredithi. Maybe tourists will come, and motels and restaurants will have to be built and the whole local economy will boom. And it all started in my yard!
Or, maybe not.