Let me get this straight. You think the SAH is a plausible hypothesis for the sudden growth in brain size, but you agree that it fails to explain or provide a mechanism for favouring genes for larger brain size?
Plausible is too weak a word, and "failing to explain or provide a mechanism" is too damning and dismissive.
I'm saying we may never know the real story, in that no single theory might ever accumulate enough backing evidence to be proven correct, by virtue of the processes being examined. SAH operates in a space where we may only find utility in thought experiments.
I can see one or two points of evidence emerging, that could simply blow SAH to bits and put the nail in the coffin of debate. But just as easily, I could see a fossil jump out of the ground, and upend our thinking overnight. The evolutionary tale of human prehistory is that brittle, based on what we have in front of us right now.
The only ways I see SAH being proven, are forward looking replication of results, or longshot statistical truths, found in subtle clues which are very hard to measure, all in one place. Meanwhile, literally any other theory could burst onto the scene with a stronger, more convincing and reasonable narrative, and bury SAH so deep in its own wild and extraordinary whimsy that we never think about it again. But neither has happened yet, so we can still navel gaze on this one.
But, take anything you want. Any externality, leveraging selective pressure, but leaving scant traces of ever even having happened, and you've got a good competing hypothesis with legs under it. Instead of psychoactive substances, why not body lice, for example, as a selective externality? Although less charismatic than SAH, just as reasonable of a story, but just as tough to tease out a smoking gun.
How would body lice influence circumstances favoring for genetic brain size? We might easily hypothesize an illness spread by one kind of louse, whereby the head lice versus the body lice is the deciding factor to produce the selective brain outcome in the same time span. But why the bigger brain on the other side of it? Same as with SAH, the brain size could be an incidental trait. That's the way bottlenecks, invasive species explosions and fitness arms races work in evolution. Some outcomes are non-deterministic, so we never get satisfying proof.
If you are able to keep things precise, please could you tell me how the ingestion of psychedelics might cause larger brain sizes to be favoured? For example, would it mean that individuals with larger brains are more likely to mate or to survive?
I'm saying we may never know the real story, in that no single theory might ever accumulate enough backing evidence to be proven correct, by virtue of the processes being examined. SAH operates in a space where we may only find utility in thought experiments.
I can see one or two points of evidence emerging, that could simply blow SAH to bits and put the nail in the coffin of debate. But just as easily, I could see a fossil jump out of the ground, and upend our thinking overnight. The evolutionary tale of human prehistory is that brittle, based on what we have in front of us right now.
The only ways I see SAH being proven, are forward looking replication of results, or longshot statistical truths, found in subtle clues which are very hard to measure, all in one place. Meanwhile, literally any other theory could burst onto the scene with a stronger, more convincing and reasonable narrative, and bury SAH so deep in its own wild and extraordinary whimsy that we never think about it again. But neither has happened yet, so we can still navel gaze on this one.
But, take anything you want. Any externality, leveraging selective pressure, but leaving scant traces of ever even having happened, and you've got a good competing hypothesis with legs under it. Instead of psychoactive substances, why not body lice, for example, as a selective externality? Although less charismatic than SAH, just as reasonable of a story, but just as tough to tease out a smoking gun.
How would body lice influence circumstances favoring for genetic brain size? We might easily hypothesize an illness spread by one kind of louse, whereby the head lice versus the body lice is the deciding factor to produce the selective brain outcome in the same time span. But why the bigger brain on the other side of it? Same as with SAH, the brain size could be an incidental trait. That's the way bottlenecks, invasive species explosions and fitness arms races work in evolution. Some outcomes are non-deterministic, so we never get satisfying proof.