Introducing the brain: why so big? Part two (Introduction)

by dhw, Friday, July 12, 2024, 12:50 (132 days ago) @ David Turell

Evolution of the brain

QUOTE: “The planarian is thus not only the first animal to possess a brain, but may be the ancestor of the vertebrate brain.”

DAVID: No organized brains in Ediacaran's found so far. They don't have heads. The gap is in the sudden organization into brains of substance.

dhw: So although the planarian is the first animal to possess a brain and may be the ancestor of the vertebrate brain, you know that it did not have a brain and cannot be the ancestor of the vertebrate brain. I get it. Is this your Jekyll or your Hyde speaking?

Not answered.

Why is our brain so big?

DAVID: […] Our brain is much too big and complicated for the single purpose of survival. Darwin's emphasis on adaptions for survival driving evolution does not fit this example. In short, human beings cannot be explained by Darwin's theory of evolution.

dhw: Of course our brain has evolved beyond the single purpose of survival! […] The question [Darwin] tackles is how species originate. […]

DAVID: Yes, we evolved from apes, who are still here, not needing any of our advances. […] Adler used Darwin's evolution theory [...] to show humans should not have appeared as no need was ever demonstrated for survival. You champion Darwin's 'survivability' as a driver of evolution. Explain how the sapiens brain improved that ability, especially since our close cousins, the apes do just fine without it. Then add all the skeletal issues that allow us to do what apes cannot.

The theory is that SOME of our ancestors encountered conditions that threatened their survival, and so they changed their environment. And this new way of life required the physical changes that led to bipedalism and new uses of the brain. Other apes survived perfectly well in their original surroundings. What’s the problem?

DAVID: Let's look at 'de novo'. Do you remember the story I presented in which the scientists had carefully dissected a small area of our brain and found how amazingly complex it was. Jumping from Erectus to sapiens brain is a major de novo design change.

No one is denying the complexity. All phases in the brain’s evolution entail “jumps” as new conditions require new complexifications or additional cells. Complications and additions do not mean that each brain is designed “de novo”(See below.)

The brain: why so big?
QUOTE: H. erectus first appeared in the fossil record about 2 million years ago, its brain volume was as little as 550 cubic centimetres. By the time the last H. erectus were walking Earth, some 108,000 years ago, that volume had doubled. (dhw: See below)

QUOTE: “Evolution doesn’t just invent new brain structures and suddenly you can speak or whatever. It’s the other way round. You start speaking and then this creates a new cultural environment under which there are new selective pressures that favour new brain structures.”

The other way round means that speaking is what changes brain structures, and we know for a fact that new activities cause such changes (the illiterate Indian women, the London taxi-drivers etc.). The author has omitted this crucial stage. But new abilities also engender new requirements – hence the continued increase in size, even within the same species (H. erectus), until size becomes limited and complexification takes over. Nothing “de novo”. Each brain adds to or complexifies existing brains.

QUOTE: "...size clearly matters at least to some extent, which raises questions about a curious event in our recent evolutionary history when brains shrank, going from 1500 cubic centimetres to just 1350 cubic centimetres..."

No surprise. It makes perfect sense that if the brain had reached maximum size for the body to support, complexification had to take over. And complexification proved so efficient that certain cells were no longer needed.

DAVID: [...] The size discussion ignores the complexity issue…

Spot on!

DAVID: ...in which a smaller brain can be more highly complex and produce unexpectedly advanced products (artifacts).

I would suggest that the artefacts produced by our ancestors were at least partly the cause of expansion: the smaller brain conceived the idea, but the implementation of the idea caused the expansion. New requirements produce changes. As above, these changes may produce more new requirements and so the process continues.

DAVID: Our bigger brain event to smaller brain by 150 cc average is right on point.

See my explanation above.

DAVID: Throughout the article no explanation appears that ever answers the question: Viewed as a natural event how do our brain get big? Adler's supernatural answer: God.

Even your God must have had some means of doing it: you suggest a 3.8-billion-year-old programme for every single species, mutation, strategy, lifestyle, natural wonder in life's history, or a personal dabble (e.g. he operated on a group of sleeping Moroccans, if I remember rightly.) If God exists, I would propose that he created a mechanism whereby existing cells had the ability to produce additional cells (expansion) and additional connections (complexification) when needed. That would explain why the vast majority of our brain structures can be found in our fellow mammals – we simply added to these. Sapiens brain was not designed “de novo”.