It is a question that has long befuddled evolutionary biologists. Why do populations of organisms become specialized? Take cave fish, for example. These creatures, which dwell in perpetual darkness, are generally blind, having either greatly reduced eyes or no eyes at all. Yet presumably they evolved from fish with functioning eyes. Granted, vision doesnt help in the cave environment, but why lose the ability to survive in other niches? Researchers have put forth two theories. One holds that unused functions can accumulate destructive mutations without affecting the creature. The other theory posits that unused functions get dropped in order to redirect the energy involved in maintaining them, enhancing useful functions. New research published in the journal Nature supports the latter idea.

In order to address this question, researchers at Michigan State University decided to simulate evolution in the lab. They raised 12 strains of E. coli bacteria on glucose alone to see whether they would lose their ability to process other sugars. Twenty thousand generations later, the team found that indeed they had. Moreover, it seems that the bacteria lost their ability to grow on other sugars because doing so made them more efficient glucose-eatersa mechanism dubbed antagonistic pleiotropy. Natural selection thus appears, at least according to this study, to favor dumping extraneous functions in order to focus on whats useful.