The occurrence of the same characteristic in different related species is usually the hallmark of a common evolutionary ancestor. However, the same trait can sometimes evolve independently, even in closely related species, a process known as convergent evolution. Understanding convergent evolution at the molecular level may shed light on exactly which genes are the tools for evolutionary change. In the August 21 Nature, two papers provide some illuminating insights into this issue by examining morphological features in different Drosophila species.

In the first paper, Nicolas Gompel and Sean B. Carroll at the University of Wisconsin describe the correlation between the expression of Bric-à -brac2 (Bab2) and abdominal pigmentation and hair pattern. The two bab genes (bab1 and bab2) are known to negatively regulate these traits in Drosophila melanogaster. Males exhibit pigmented stripes and two heavily pigmented abdominal segments (caused by bab2 downregulation), whereas females have...

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