The researchers, one team at MIT and one at the University of Utah, examined E. coli bacteria, the kind that live in the human gut. The bacteria lacked a gene that digests lactose-milk sugar-so the researchers put the microbes in a dish containing nothing but. Rather than dying of starvation, the colony of E. coli developed, 100 times more quickly than Darwinian evolution allows, a mutation that enabled them to eat lactose. That much had been reported last year, too. But the latest experiments give skeptics an,explanation of how the bacteria seem to anticipate desirable mutations. It has to do with what passes for sex in the microscopic world: the transfer of a circle of DNA called a plasmid, in this case containing a gene that digests lactose. It happens that the systems controlling bacterial sex rev up when a bug is starving, the researchers report-exactly the situation of bacteria unable to digest lactose. Adaptive mutations probably don’t work this way in higher organisms like giraffes and moths. But if primitive organisms preferentially acquire traits that help them survive, biologists will have to admit that, 136 years after “The Origin of Species,” evolution still holds surprises.
