杏吧原创

CHARLES Darwin can still teach scientists a thing or two. Research on two creatures鈥� mating habits has overturned half a century of dogma by showing that natural selection alone can help create new species, just as Darwin predicted.

Since the 1940s, biologists have believed that a species could split only if a geographical barrier 鈥� such as an ocean or a mountain range 鈥� separated two populations and prevented them from mixing. But Australian and American scientists have found that this isn鈥檛 necessarily so.

They have shown that natural selection can change the way both fish and flies recognise their prospective mates, a process which can lead to two groups rapidly diverging, even when they live together in the same place. This process of reproductive isolation only takes a dozen generations or so, making it faster than anyone thought possible.

The findings raise the intriguing possibility that people could quickly split into different species. Given the right conditions, groups of humans might evolve so fast that they become isolated from each other in as little as 300 years.

鈥淭here鈥檚 no reason why mate recognition in any species couldn鈥檛 evolve so rapidly,鈥� says Megan Higgie of the University of Queensland in Brisbane. 鈥淚 don鈥檛 see why it couldn鈥檛 be possible in humans,鈥� agrees Andrew Hendry of the University of Massachusetts in Amherst, although he points out that our choice of mate is complicated by cultural influences.

Higgie and her colleagues studied the effects of natural selection on Drosophila serrata fruit flies. When Higgie put these flies with a similar species called Drosophila birchii, the D. serrata males wasted half their time trying to mate the females from the wrong species, hence losing valuable opportunities to pass on their genes.

But within just nine generations this selection pressure had forced them to alter their pheromones to only recognise their own kind. 鈥淭he trait under selection, mate recognition, is an important one,鈥� says Higgie. 鈥淢ake a mistake, and you might not contribute to the next generation.鈥�

Meanwhile, Hendry and colleagues at the University of Washington in Seattle studied sockeye salmon in Lake Washington. The fish had been introduced into a river upstream of the lake in 1937, but many had taken to spawning at a beach on the edge of the lake.

Hendry compared fish that spawned at the river with those that spawned at the beach. He found differences in both their appearance and their genes, even though the fish were swimming between the two areas. The genetic differences were not great, but were large enough to show that the populations had somehow become reproductively isolated from each other in fewer than 13 generations. 鈥淚t is speciation in action,鈥� says Hendry. 鈥淭his is the first time it has been shown to happen this quickly in the wild.鈥�