Experts have differed about where the genus Varanus (monitor lizards) originated. Because most existing species live in Australia, early researchers concluded that Varanus originated in Australia and subsequently island-hopped westward along the Indo-Australian archipelago. Herpetologist Robert Mertens later argued that Varanus probably originated in the archipelago. Chromosomal analysis has since supported Mertens' contention, and in addition, geologic evidence points to a collision between the archipelago and the Australian landmass after Varanus evolved – a fact that could account for the genus's present distribution. A related puzzle for scientists is the present distribution of Varanus' largest surviving species, the Komodo dragon. These carnivores live only on four small islands in the archipelago where, scientists note, the prey base is too small to support mammalian carnivore. But the Komodo dragon has recently been shown to manage body temperature much more efficient than do mammalian carnivores, enabling it to survive on about a tenth of the food energy required by a mammalian carnivore of comparable size.