Giant leaps, not small steps

The interplay between genes and the environment results in adaptive evolution. Evolution of biomolecules was thought to occur by single, minor changes in the DNA sequence resulting in a gradual shift in function until a substantive change is selected for, but calculations of the time required for this to occur sometimes resulted in estimates longer than the age of the Earth. Current thinking suggests single changes causing major phenotypic effects to be at the root of adaptive evolution. In the November 13 Nature, H.D. Bradshaw and Douglas Schemske at the University of Washington report the breeding of near-isogenic lines (NILs) of the Mimulus flower by backcrossing two species pollinated by two different means—one by the honeybee and the other by the hummingbird—so that a gene controlling flower color from one species was substituted into the other. Their analysis showed that the effective swapping of the flower color allele...