Human evolution; savannah theory fading (Introduction)

by dhw, Thursday, July 14, 2022, 09:15 (646 days ago) @ David Turell

DAVID: The erectus brain developed in Africa and the erectus wandered all over the Earth handling new environments with ease. You can talk all around that without changing the import of that history. The brain came before all the required uses in subsequent migrations.

dhw: Why have you suddenly skipped millions of years and hominins and homos? The subject is human evolution. Our history reaches back millions of years to small-brained hominins who apparently still lived in forests, although it is possible that their environment was mixed. Lucy’s brain capacity was about 400 cc. What you call the “new big brain” was the result of expansion over millions of years as hominins and homos encountered new conditions and environments. We know the brain RESPONDS to new requirements. When you say: “The brain came before all the required uses”, yes, the little brain was there from the start, and it gradually became bigger as it learned to cope with or exploit new conditions, but Lucy was not born with the “new big brain”! Even erectus wasn’t born with the “new big brain”, since his/her brain appears to have expanded from approx. 850 cc to 1000 + cc. I’d hoped to avoid a repetition of our discussion on brain expansion, but you still seem to be hooked on the notion that every expansion was a divine dabble IN ANTICIPATION of new requirements.

DAVID: I agree the Erectus brain increased over time, but a key thrust of the article is Erectus migration from Africa all over the world, as I stated above and from the article:

I can only comment on the material you present to us. However, the extra material about erectus makes no difference to the argument. He was already “upright”, and “the first expansions of our ancestors beyond Africa have often been associated with periods of climate change that would have resulted in the extension of grassland ‘corridors’ out of Africa.” This clearly suggests that changes in living conditions coincided with changes in behaviour, and you have inadvertently explained the process of brain expansion in your comment:

DAVID: The brain came first and the migration afterward and did enlarge within the same
species as new experiences occurred.

The brain expands when it has to cope with new experiences that exceed its existing capacity. From the time when our earliest ancestors descended from the trees, there was a continuous expansion in response to new experiences. Yes, erectus came long after those earlier times and expansions, so when he migrated, he already had a bigger brain than his own ancestors, and then new experiences resulted in his own brain expansion. Thank you for confirming the sequence of the process: new experiences result in expansion.

DAVID: Note! In contrast to our brain shrinking with new complex advanced uses. Why? I view us as a completed endpoint while Erectus was a work in progress as God designed it.

This is what I wanted to avoid. We have been over it again and again. Why would your God have given us a brain bigger than was needed? A miscalculation? I propose that our brain had reached a point beyond which further expansion might have caused problems in the rest of the anatomy, and so the process of complexification (which had always existed) took over completely, and proved so efficient that some existing cells were no longer necessary. Hence shrinkage.