Most of you have seen pictures of bodybuilders posing, mighty muscles flexed. After a few moments, though, any one of them begins to look pretty much like another, yet you know that underneath those bulging muscles lie real differences. This is a form of convergence, where body form becomes almost indistinguishable under the influence of a similar environment—in this case, hundreds or thousands of hours devoted to lifting weights.
A similar thing happens in the natural world, except it's a genetic
rather than individual response to the environment. Environments shape species in that
individuals most fit for them tend to survive and those less fit to die. Species having
nearly identical ecological niches and living in similar, though geographically
separate, environments thus frequently come to resemble one another. The kangaroo rats
of our Southwestern plains and deserts look very similar to the jerboas of arid Africa
and Eurasia, and even the marsupials of Australia get into the act with such animals as
the Kultarr—like our bodybuilders, looking much the same superficially, but underneath
are vast differences.
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.