A classic way of thinking about natural selection is as a landscape of mountain peaks rising out of a plain, each peak representing an ecological niche. The higher up an organism gets, the better its fitness for the niche, and the more fit you are, the more likely to survive to reproduce those adaptive features. In that model, then, once an organism begins to climb a peak, it can go in no direction except up since the environment picks off those less well adapted.
In a stable world, then, we would expect each kind of organism to be
perched on the top of a peak. But the world is not stable, tending to be more like an
ocean, with only a few islands standing above the rising and falling waves. The
specialist, having lost its flexibility, dies when a peak vanishes beneath the waves.
The generalist, surviving after a fashion on wave top and in wave trough, is the one in
it for the long term. The moral? Things change—survival means being able to change with
them!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.