According to Darwins theory of evolution....?

I agree with Labsci. According to evolutionary theory, it is meaningless to call any organism more "highly evolved" than another (so they are either *all* "highly evolved", or none are). The "highly evolved" language is very tempting for humans to slip into because we are used to thinking of ourselves as somehow more "highly evolved" than other organisms ... but on a purely biological basis, there is no basis for that conceit.

All that matters is what survives, and this is completely environment dependent. On the Sahara desert a camel is more "highly evolved" than we are, at night in the amazon jungle; a treesnake is more "highly evolved"; in the middle of the ocean, a great white shark is more "highly evolved"; and for 160 million years the dinosaurs were very "highly evolved", until a meteor strike changed that rather quickly, while little rodent-like mammals turned out to be better survivors.

No Darwin argued for the descent of all modern species from a single common ancestor in our planet's distant past. He proposed a more or less correct mechanism and described the system in question accurately enough to allow him to draw some very good inferences from even the limited amount of information that he had. In any event if you thought that Darwin was not arguing for common ancestry you need to read the book again.

Much as I hate to disagree with top contributors, "highly evolved" does not mean well-adapted to its environment. I would define "highly evolved" as specialized --- having diverged the most from its ancestors, That might make something like a hummingbird "highly evolved." By comparison, we humans are quite generalized.

According to evolutionary theory all animals are adapted to their current environment, none is "more highly evolved" than any other. An earthworm is as evolved as a human.

If longevity of a species is a measure of success, we would have to wait a few hundred million years to prove ourselves.

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Darwin was the natural selection guy, so he might have picked an organism that's become even more well-adapted than humans. Maybe one from the primate genus, such as the chimpanzee?

He would probably say Humans