(Vanity) Chiefly on Squirrels, or, Darwin meets The Michelin Man

While driving into work recently, I had a near encounter with a squirrel. I'm sure most of you have had one too. What generally seems to happen is this. The squirrel goes to the edge of the road, and looks around. Then, just when your car gets within range, the squirrel darts in front of you, seemingly trying to see how close it can get to being squished, without actually dying. As an added bonus, sometimes, just as you break, or swerve the other way, it will change course. If you are really lucky, sometimes the critter will zigzag three or four times before careening across the other lane, or returning from whence it came.

Sometimes, if the squirrel is un-lucky, it won't make it. We have another subject for the Calvin and Hobbes "Be Careful, or Be Roadkill" poster.

Now, the thing which annoyed me -- aside from the "poor little thing" factor, or the inconvenience of swerving -- is the question, "Why can't the little buggers make up their minds?" And the answer struck me -- this is an instinctive, reflexive behaviour -- a small animal running away from a predator will probably get away more often, if it zigzags unpredictably. Each time it zigs, the hunter has to notice, adapt, and change course to match. And since the squirrel is smaller and more nimble, each time it reverses course, it probably gains ground. So this is a workable survival tactic -- as long as you are really being chased by a predator, instead of menaced by steel-belted radials backed by thousands of pounds of steel, which continues more or less in a straight line. In fact, a lot of people would call this an evolutionary adaptation.

Now, I'm not here to start a flame war, but just to ask a couple of interesting questions which this raises. First of all, if this zig-zag evasion is an evolutionary advantage, since those squirrels who don't zig tend to be lunch, and so don't breed as well as the ones who get away, why haven't we seen an evolutionary adaptation? After all, running like blazes in a straight line is more likely to get you across the road safely than doubling back in front of a Toyota. Even if it is an "eco-friendly" model like the Prius. However, this may be over-simplifying things, so let's examine this a little closer.

Exactly how long does it take for natural selection to work its magic? Cars have been on the scene for what, a century or so? In biologic time, that's nothing. And yet, according to the predictions of "punctuated equilibrum", once a sufficiently advantageous change *does* occur, it spreads through the population like wildfire. Then again, some people might object that the opportunities for natural selection in this situation or a bit overstated. What is the relative percentage of squirrels who die from "close encounters of the worst kind" with the Michelin Man ? Remember that adaptations and selection pressure are statistical phenomena. And if the number of squirrels eaten for failing to zig, greatly outnumber those squished by zagging too much, then you're not going to see any change in squirrel behaviour soon. Maybe a 0.1% increase in the chance of survival just isn't enough to select one gene over another?

But all this talk of zigging and zagging brings up another possibility. After all, while a lot of the country is urbanized, and squirrels *do* live in the city, there are large parts of the country which are undeveloped, where there are relatively few roads. Wouldn't it be reasonable to expect two separate subgroups of squirrels? One of which lives in the country, and is adapted to carnivores, and another group that lives in the city, and is adapted to cars?

And that brings up one final question. Suppose, just for kicks,that there are two subsets of squirrels around. Let's call them the zigzags (country) and the skid marks (city). How far away from the city do you have to get before the evasion behaviour of the squirrels change? Let's say a couple of squirrels on the boundary of the city -- one a zigzag, one a skidmark -- fall in love and have a nest of young squirrels. By natural selection, of course, those of their young who zig or skid incorrectly will be eliminated from the breeding stock, and the others will survive. The question is, how long does it take for the powers of natural selection to choose one of these genes over the other? (Does one become dominant and one become recessive?) Or, if you really do have two different populations, how many more of this sort of change have to occur before the ziggers split off from the skidders, and you really have two different species?

Tune in next week, when we discuss what cats used to do before there were humans to get them down from trees.

After 50 years of driving, I've only struck one critter, and that was a large rabbit at night. It stopped on the "double yellow" and couldn't have picked a worse time to leap in front of my left tire. Fortunately, no odor ever wafted out from under my truck.

I think there will be a slow, but inexorable, survival benefit to those who adapt their ways to our approaching four-wheeled machines. They still have to master the efforts of their chief predators, however.

The use of a horn "toot" sends nearly every critter (including birds) from the roadside, and I highly recommend it.

My contribution here is derived from a friendly association I have made here with chipmunks. Once I've sighted them, I have trained them to immediately race towards me for a sunflower seed reward. It's funny to see them whirl from their intended path to directly respond to my whistle!

(The horn toot has no conditioned-reward intended).

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.