emergence

Evolutionary geneticists reveal that disease genes emerged very early in evolutionary history. They have systematically analyzed the time of emergence for a large number of genes -- genes which can also initiate diseases.

When a young gene known as sphinx is inactivated in the common fruit fly, it leads to increased male-male courtship.

Such behavior is widespread in many fly species, but not in Drosophila melanogaster, which has the sphinx gene.

Other fly species do not. When two D. melanogaster males that lack the sphinx gene are put together, they court each other.