11/15/2010 02:57 pm ET Updated Dec 06, 2017

Snake Gives Virgin Birth to Bizarre Offspring

You might be surprised to learn that virgin births occur in nature, not just in religious tradition and mythology. Some insects and other invertebrates commonly reproduce by parthenogenesis, the cloning process through which a female produces viable eggs without mating with a male. Parthenogenesis, however, is not normally seen in vertebrates. Vertebrates reproduce sexually, with a male contributing genetic material to the female during the mating process, which combines with the female's to form offspring that have a blend of their parents' DNA. At least usually.

Recently a strange new species of butterfly lizard was documented in Vietnam. Scientists discovered, to their surprise, that all of these lizards are female and reproduce by parthenogenesis just like invertebrates. Komodo dragons, hammerhead sharks, the Amazon molly and some other bony fishes have also been proven to reproduce asexually in this manner as well.

But perhaps the most shocking example of virgin birth in a vertebrate is the female boa constrictor that not only gave birth without mating with a male, but whose offspring were a bizarre genetic variant.

The snake was housed with four potential male mates, but when her litter was born (boas have live offspring rather than laying eggs like some other snake species--see video below) scientists knew something strange was going on. The babies all showed a rare recessive coloration that the mother carried but not any of the normal-colored males, which essentially ruled out the possibility that any of those males contributed genetic material. On top of that, all the babies were female. In other documented cases of vertebrate virgin birth, the babies are all male.

It turns out that these baby snakes have a rare genetic makeup that has never been documented in a vertebrate outside of controlled experiments in a lab. To understand why, a refresher in basic reproductive genetics is helpful. In many species, including snakes and humans, male and female parents contribute their genetic material in the form of chromosomes based on their biological gender, the combination of which then determines the gender of each individual offspring, among other things. In snakes, the male contributes the Z chromosome and the female the W. Normal males have the ZZ combination of chromosomes and normal females have the ZW combination. (In humans, males are XY and females are XX.)

The female babies of this particular boa, however, turned out to be all WW, making them half-clones of their mother and the first documented case of a vertebrate giving birth to babies with this genetic makeup.

No one knows why or how this happened. Yet. For me, this is just more proof that despite major advances in technology and the exponential expansion of our collective scientific knowledge in just the last few centuries, we still have a long way to go in understanding the biology of our planet. A future rich with new biological discoveries and understanding, sometimes bizarre, is an exciting prospect indeed.

VIDEO: Watch a boa constrictor give live birth.