Eekily, Squeakily
M. m. domesticus
Mates with its cousin,
Algerian mouse—

Gains a resistance to
Anticoagulants—
Most of the poisons you’d
Use in your house

If you introduce a selection pressure on a population, you’ll get evolution (unless you get extinction). Via the Beeb, a story on mouse evolution in response to our selection pressure, poison. In particular anticoagulant rodenticides, which cause death through massive internal bleeding (which is why you don’t want your pets getting into the mouse traps). A mouse with a resistance to such poisons would have a decided advantage, in an environment where such poisons are present.

In this case, house mice (Mus musculus domesticus) bred with Algerian mice (M spretus), and as you might expect from inter-species mating, most of their offspring were sterile. As a general rule, mating outside your species is not terribly adaptive. All other things equal, it is not a good reproductive strategy. Ah, but with a selection pressure like anticoagulant poisons in the environment, the few fertile hybrids were at a selective advantage over their purebred peers. Most of the hybrids, sterile, died without reproducing; the few fertile ones survived and reproduced; this is the very engine of natural selection (well, one path).

The fascinating part about this, to me, is the clear demonstration of the effect of specific environment. If not for the pressure of rodenticides, the hybridization strategy would be at a strong disadvantage, given that the majority of the offspring are sterile. But a particular environment can and does make a strategy useful where it otherwise would not be. This happens, of course, in other versions of selection as well, such as operant learning and cultural change.

A behavior that is, on the face of it, self-destructive–like self-injurious behavior–can be used in an institutional setting to avoid doing work, or to manipulate caregivers into giving attention (it is very difficult to ignore someone hitting or biting him/herself). This can be tremendously adaptive, in the right environment.

An evolutionary model reminds us that all situations are not created equal, and that a strategy that has been shown to work in one situation cannot be expected to work in all. Of course, in this model we only find out what works by seeing everything that doesn’t work… well, die. It’s not an efficient or humane strategy. And it sure as hell doesn’t look intelligently designed.

But in its way, isn’t it just beautiful?