University of Illinois Professor Charles Whitfield and postdoctoral researcher Amro Zayed analyzed the genes of honey bees in Africa, Europe, Asia and the Americas. The researchers were looking for tiny variations in the sequences of nucleotides that make up all genes.

By comparing the genes in bees from different geographic territories, the researchers determined invading bees weren't randomly acquiring genetic material from their predecessors by interbreeding but certain genes from the previously introduced bees were giving the newcomers an advantage.

When the African honey bees mated with the western European honey bees that had been in South America for centuries, one might expect the hybrid offspring would randomly pick up both the functional and non-functional parts of the genome, Zayed said.

"Those African bees are doing better because there were western European honey bees there for them to mix with," he said. "Now we can say we have a signature for evolution in the genome."

The study appears in the early online edition of the Proceedings of the National Academy of Sciences.