[Almost] Convergent Evolution?

The Monitor Lizards (Varanus) and the large Tegus of South America (Tupinambis) are sometimes cited as being examples of convergent evolution. The beaded lizards aside there are no true monitor lizards in the new world so it is widely believed that the whiptails (small, skink-like lizards) adapted to take over the niche of large-carnivorous lizard.This is particularly important when comparing their respective ecologies: the Nile Monitor is the dominant predator of Nile Crocodile nests while the Common Tegu is the dominant predator of caiman eggs. Both also apparently exhibit exceptional physical endurance for reptiles, although I personally can't testify to that from observation.There seem to be HUGE differences in human interactions however; as in monitors make lousy pets while certain Tegus (Red and Argentinian Black and White) are terrific by most standards. Is there any real explanation as to why some of the Tegu are much more sociable with humans while the monitors are not? I should point out that the Arg B&W Tegu is an omnivore and the Red is an herbivore. Almost all of the monitors (the ones kept as pets anyway) are strictly carnivorous as is the Common Tegu (which is equally as unsociable).I seriously doubt that their diet has any real bearing on their attitude: Iguanas are strict herbivores and they can be just as ill-mannered as the monitors.Obviously these lizards didn't evolve to be sociable with people and they certainly didn't have captivity in mind. However, neither did the monitors outside of Africa or the Iguanas/ Does anyone here have any ideas as to how sociability in these lizards could have first developed or why it was preferential to their survival? And what do you think of the possibility of true, legitimate animal domestication among reptiles?In truth the "False Monitor" (Tejvaranus/Callopistes flavipunctatus) is a far better example of convergent evolution because it actually looks like a monitor as an adult. The actual Tegus, in my opinion, only look like monitors as babies (my avatar). Both the False Monitor and the Tegus are very closely related though, so the point remains.

This topic in of itself doesn't have much to do with an Evolution/Creationism controversy since to really answer the question, one must already assume evolution to be true. This would be something for one of the less relevant sections, like coffee house I guess.