Scientists provide the first quantitative genetic evidence of why replaying Stephen Jay Gould’s “tape of life” would produce different results each time.From the press release:
Scientists have recreated natural selection in real-time in the laboratory and provide the first quantitative evidence for natural selection on so-called standing genetic variation – a process long thought to be operating in natural populations that reproduce sexually but which, until now, had never been demonstrated.
They used the fruit fly, Drosophila melanogaster, derived from an original group of flies, harvested from the wild back in 1975. These ancestral flies were grown in the laboratory, for two decades, under different environmental conditions, (such as starvation and longer life-cycles) so that each population was selected for specific characteristics. Then scientists placed these populations back in the ancestral environment for 50 generations to impose reverse evolution on the flies, and then looked at the genetic changes in certain areas of chromosome 3 of these flies.
Says Henrique, 'In 2001 we showed that evolution is reversible in as far as phenotypes are concerned, but even then, only to a point. Indeed, not all the characteristics evolved back to the ancestral state. Furthermore, some characteristics reverse-evolved rapidly, while others took longer.
Reverse evolution seems to stop when the populations of flies achieve adaptation to the ancestral environment, which may not coincide with the ancestral state. In this study, we have shown that underlying these phenomena is the fact that, at the genetic level, convergence to the ancestral state is on the order of 50%, that is, on average, only half of the gene frequencies revert to the ancestral gene frequencies – evolution is contingent upon history at the genetic level too'.