tl;dr the presence of exactly the same gene in reproductively isolated species has puzzled scientists for some time. The example cited were two different very cold water fish which both have exactly the same “antifreeze” gene.

This research group identified a type of transposon that infect worms with a virus-like ability to penetrate cells and “infect” hosts. Transposons are “greedy” particles that “transpose” DNA in order to reproduce, often at the expense of their hosts. While doing this, entire genes may be transposed.

The transposon itself likely gained this ability from an encounter with a virus.

Fascinating.