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Desert Diary
Biology/Jury Rigging


Duct tape and bailing wire, chewing gum and string, jury-rigging. Whatever terms you're familiar with, they all mean the same thing—making do with what you have. Why are scientists using such terms? Simple—jury-rigging is a fact of life in evolution. Time and again we see structures that are used for a particular function in one group of animals or plants diverted to a different use in another group. Indeed, this fact helped persuade scientists that organisms really evolved, rather than being designed from scratch.

A simple example from animals in our own desert may clarify things. Look any cow, sheep, pronghorn antelope, or deer in the mouth, and you'll see a graceful arch of eight lower teeth, incisors used for cropping vegetation. But there's something strange. No other placental mammal has more than six lower incisors. Where did the extra two come from? Easy to answer. The fourth incisor on each side is really the canine tooth, transformed from a piercing and ripping tooth to the appearance and function of just another incisor.
pen and ink


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.

deer incisors

Looking down on the lower "incisors" of a deer. The posterior tooth on each side actually is the canine. Photograph by A.H. Harris.