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Desert Diary


Most of us have seen diagrams in biology or geology books showing the skulls and feet of horses grading from those of tiny Eohippus at the bottom to the modern horse at top. Although legitimate, this unfortunately implies to some that that's all there is to equine evolution. If indeed that were all, the now discarded idea of orthogenesis would have a strong bit of evidence.

In the late 1800s and early 1900s, some biologists thought that evolution occurred in a straight line without deviation, as if evolving toward a goal. Thus the idea that early horses were destined to lose toes and develop increasingly complex grinding teeth until Lo!, they became today's horses. Fortunately, orthogenesis was a testable hypothesis--and when tested, failed. We now realize that horse evolution was more like a bush than an arrow. Only one twig made it to the present, but evidence of a wide variety of horses is plain in the fossil record. Look closely at our Chihuahuan Desert fossil beds, and old three-toes is with us nearly to the end.
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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.