Extra bit 2: Metalworking technology in the new world went in a very different direction than the old world. Possibly because it was invented after social stratification had fully developed, instead of before/at the same time: for whatever reason, Mesoamerican and Incan smiths were focused on making decorative objects, and the utility of metal for making tools was a secondary consideration. A lot of effort went into making different colours of bronze, making it look like gold or silver, etc, rather than finding optimum ways of making it a superior substitute for stone. Again, inventions are embedded in the context of their culture and the rest of the society's technological base at the time they are discovered. Rewind history and run it again, and the people of Ur might not have developed bronze until thousands of years later, or might have only used it to adorn temples and never for tools.