"Brain size doubled from afarensis (Lucy types 3.5 mya) to erectus, and jumped by 50-100% to us in a matter of a few tens of thousands of years or less."
The "jump" you refer to from ergaster (slightly less than 1000cc) to heidelberg (not erectus) at a slowly increasing capacity, to archaic sapiens with around the current average of 1300cc, is over a period of more than 500,000 years...not "a few tens of thousands of years or less".
The "jump" you refer to from ergaster (slightly less than 1000cc) to heidelberg (not erectus) at a slowly increasing capacity, to archaic sapiens with around the current average of 1300cc, is over a period of more than 500,000 years...not "a few tens of thousands of years or less".
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