[contoraria]

> The languages spoken by today's ... are not systematically and fundamentally different ...

That is a meaningless statement, when there is no consensus on the fundamentals of language, and more so because the Languages of the world differ variously.

I'm not sure what you think how complexity of language is measured. Certainly, there are terms and expressions that had to be invented along with the concepts that they describe, which hunter gatherers don't know, and that's not limited to technology. Emotional content would be much more important on a human scale. I think the question would have to be, whether everyone was able to speak. Which term would the analogous to "literate"?

[bloak]

I think we basically agree.

The only way I can think of for measuring the complexity of a language is an inaccurate empirical one: see how hard it is for speakers of unrelated languages to learn it. That approach would probably confirm that Hausa is harder to learn than Bahasa Indonesia, for example, though whether that's what other people mean by "complexity", I can't say.