Today's interesting fact is a continuing note on Komodo Dragons.

There is speculation that the Komodo Dragons are the last remnants or descendants of a species that once lived in Australia and Indonesia, which were connected 900,000 of years ago. The large lizards in most of Indonesia and Australia disappeared around the same time that humans arrived. It isn't known of course, if these large lizards died out because of the climate change that was then occurring or if humans had something to do with their demise.

Komodo Dragons are one of the few lizards where the female of the species do not require a male to reproduce, or at least to produce male progeny. Komodo Dragons, like birds, and unlike crocodiles and many other lizards, have genes that determine the sex of their offspring. Instead of XY, Birds and Komodo Dragons have an ZW sex pair. Many lizards have their sex determined by the heat the eggs receive during development.

Female Komodo Dragons have the ZW combination whereas Males are ZZ. This is the opposite of Humans. When Female Komodo Dragons don't have males to fertilise their eggs, they effectively self fertilise, by somehow doubling the the chromosomes in the egg. Eggs that have a WW combination, the eggs are infertile and do not develop. If they have ZZ they are male. All young from parthenogenesis in Komodo Dragons have been male, which makes sense, as the female's eggs would either have W or Z, the second sex chromosome would normally be supplied in the male's sperm, as a W.