(Related: "'Virgin Birth' Record Broken by Hotel Shark.")

Among vertebrate animals that normally reproduce sexually, virlgin birth, or parthenogenesis, had been observed in only captive female snakes, Komodo dragons, birds, and sharks.

Until now it's been considered an evolutionary novelty, albeit one that made a sort of sense—a way for a bloodline to continue in the absence of suitable fathers.

For the study behind the find, published in this week's issue of the journal Biology Letters, a team led by biologist Warren Booth of the University of Tulsa in Oklahoma captured pregnant copperhead and cottonmouth (see picture) females from fields where males were present. When the snakes gave birth, the researchers documented the physical and genetic