Obsidian is extremely sharp but also extremely fragile, so it was much more often used as a tool than as a weapon. I think that a lot of the discovered obsidian weapons were more about prestige than practicality -- obsidian was a valuable and limited resource.Obsidian cuts better than iron (or steel), but iron is cheaper and lighter--and when the goal is to lacerate your opponent into bleeding to death, the precision cuts of obsidian aren't a significant advantage. (There are investigations into making scalpels out of obsidian, though--an application where precision cuts are highly desirable.)
And they don't use obsidian as a scalpel for this very reason -- the last thing you need is shards of glass breaking off in the patient, and while you can easily sterilize steel with high temperature steam, this same method will destroy glass.
Civilization (the game) is at its core about city-building, and that really only became widespread around the 4th Millennium BC. Recent iterations of the game have delved more into cultures that really don't fit the description of city-builders, but they're still modeled as city-builders. Modeling the earliest known human technologies is well beyond the scope of the game... human technology stretches back millions of years to pre-Homo sapiens ancestors. As much as I like the idea of playing a game about prehistoric hunter-gatherers, I don't think Civilization is that game.This confirms that Civ game begins should be earlier than 4th Millenium BC.
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