Herpetologists used to believe that like most vertebrates, Komodo dragons always reproduced through sex. However, in recent years, a couple of zoological institutions who had only female dragons on site were very surprised to learn that the girls were able to produce viable young through parthenogenesis (i.e. laying fertile, but non-fertilized, eggs). For genetic reasons too boring to describe, the offspring are always male (on the other hand, if you really want to know the details about the sex chromosomes and all that stuff, just read this article from Scientific American).
Once a female dragon is put back in an environment where males are available, she will revert to normal sexual behavior and breeding.
In a normal egg, half of the chromosomes are provided by the mother and half by the father. At some point in the formation of the parthenogenetic egg, the set of chromosomes provided by the mother double, ultimately yielding the baby with a full set.
Sexual reproduction is normally highly favored evolutionary-wise because it reduces the chance of producing individuals with full pairs of recessive genes and the resulting genetic illnesses. In addition, if a population is highly similar genetically, an infectious or environmental disease is more likely to wipe out all of the individuals and not just some.
In the case of the dragons, the above policy considerations are sometimes suspended due to the fact that female Komodos are at risk of washing ashore on one of the many thousands of small islands in Indonesia without having a male to keep them satisfied (what the male dragons do in a similar situation is probably something on which we should not speculate). By using parthenogenesis, the female is able to produce males who, when they mature, will be able to satisfy their Oedipal fantasies by having sex with their mother and establish a breeding colony.
Although the Komodo dragons' sexless reproduction was not known at the time Michael Crichton wrote Jurassic Park, he nonetheless had the prescience to have the dinosaurs in his story, which were all female, reproduce parthenogenetically. This possibility is one reason why Tyrannosaurs, if actually cloned one day, would probably not make good house pets. The litter box detail is another.
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