In order to linkurl:evolve; novel traits, organisms may depend upon smaller, less dramatic mutations that they amass through their evolutionary history rather than suddenly acquiring a single mutation that gives them drastically different phenotypes, according to a study published online today (Jun 2) in __PNAS__. Whether an organism arrives at major evolutionary innovations through a single key mutation or a history of many accumulated mutations has been hotly debated by evolutionary biologists. The findings are "perhaps the most rigorous, clear-cut demonstration of the role of historical contingency," in evolution, said linkurl:Richard Lenski; of Michigan State University, the study's main author. Examining linkurl:__E. coli__; cultures that his lab has maintained since 1988, Lenski found that one population of the bacterium had evolved the ability to metabolize citrate -- an unprecedented trait -- after more than 30,000 generations, or approximately 15 years. So Lenski and his colleagues consulted their "frozen fossil record,"...

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