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>>>For example, the human brain did not suddenly expand 150,000 years ago with the appearance of modern humans, but about 1.5 million years ago, when brain size doubled for the first time and then continued to do so. <<<

I think I read about this happening somewhere else, although the timescale was a bit different.

From the Bible, Genesis 3

2 The woman said to the serpent, "We may eat fruit from the trees in the garden, 3 but God did say, 'You must not eat fruit from the tree that is in the middle of the garden, and you must not touch it, or you will die.' "
4 "You will not surely die," the serpent said to the woman. 5 "For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil."
...
16 To the woman he said,
"I will greatly increase your pains in childbearing;
with pain you will give birth to children.

Why did the brain need to double in size? Maybe to contain the knowledge of evil as well as good. And what is the result of a larger brain size--a larger head, making it harder to give birth.

I know this is all a stretch, but it is interesting nevertheless, and certainly no less of an extrapolative speculation that the original article.