One misconception about evolution is that it is all about a drive for more complexity.
Of course, when you start from extremely simple, as life at its beginning necessarily
was, almost any change in an organism can be seen as producing greater complexity.
Nevertheless, once a given degree of complexity is reached, we often see a tradeoff
between areas of complexification and simplification.
An example of this is the lower jaw of vertebrates. By the time fish
had evolved, the lower jaw consisted of a number of bones on each side. In various
lines of evolution, but especially in the line of reptiles leading to mammals, some of
these bones were lost. In mammals, and only in mammals among living creatures, a single
bone is present on each side. But mammals also have, in a sense, more complex ear
regions than other vertebrates—thanks to three of the bones on each side being co-opted
by the ear region. It's undoubtedly happenstance, but "to jaw" means to
talk long-windedly, and what better audience than the auditory offspring of the jaw
itself?
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
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.
Left lower jaw (dentary bone) of a Coyote (Canis latrans) with teeth labeled. Note that the entire structure is a single bone. "C" = canine. Laboratory for Environmental Biology specimen.