I know of no confirmed historical evidence of wheelbarrows being used until around the time of the Peloponnesian War in Greece, and as I understand it they subsequently vanished in the Greco-Roman world for roughly 1600 years until being reintroduced in the Middle Ages. Likewise, wheelbarrows are not evident in Chinese history until the first or second century AD.
So wheelbarrows are an application of wheels, but they're a much later application of the technology, one that did not arise historically for two to four millennia after the invention of the two or four-wheeled animal-drawn cart.
If we use a broader definition of wheelbarrow as "hand cart," we have older evidence stretching back at least to the ancient Indus Valley some time in the second or third millennium BC.
But if we stick only to inventions we have historical evidence of, there's still a gap of thousands of years between the invention of the wheel and the invention of the hand cart throughout Eurasia. The fact that Montezuma's Aztecs made no use of the wheelbarrow, rickshaw, or hand cart is hardly more remarkable than the fact that Charlemagne's Franks didn't, either.
Excellent points, but I think:
The fact that Montezuma's Aztecs made no use of the wheelbarrow, rickshaw, or hand cart is hardly more remarkable than the fact that Charlemagne's Franks didn't, either.
and:
it's quite mysterious that those civilisations invented the wheel, and then didn't bother to use it.
are not inconsistent, and are both true.
We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.
Major types of hints are:
Data for:
Data against:
To me it looks like life, animals with nervous systems, Upper Paleolithic-style Homo, language, and behavioral modernity were all extremely unlikely events (notice how far ago they are - vaguely ~3.5bln, ~600mln, ~3mln, ~200k or ~600k, ~50k years ago) - except perhaps language and behavioral modernity might have been linked with each other, if language was relatively late (Homo sapiens only) and behavioral modernity more gradual (and its apparent suddenness is an artifact). Once we have behavioral modernity, modern civilization seems almost inevitable. Your interpretation might vary of course, but at least now you have a lot of data to argue for your position, in convenient format.