Well, I tend to think of the repititions in two ways, each with its own context. One is allele frequency, such that gaps of funtional utility are created with ineffective codons, to create timing effects and distance oriented partitioning of productive segments as enzymes crawl the unzipped, live genome.
The other is more about radiation hardening, and those are full, bulk duplicates of chromosome sets, like the hexaploid grain genome that was recently being discussed last week.
But I wonder when that sort of radiation hardening aspect was selected for? Millions of years ago? Billions of years ago? Or was it all just an accident, never selected for or even put to use? If we, as humans, only have a set from each parent, I’d estimate that bulk duplication doesn’t seem to offer real benefits in the radiation hardened sense, or everything would have more copies for billions of years.
Sometimes food is prepared for flavor, based on a consensus of what tastes the best.
If more people affirm that a given recipe is the most desirable, it would be completely ridiculous to impose a lesser recipe upon the menu, if it sells poorly.
I can easily prepare low sodium pretzels, and try to sell them at the county fair, but what good would that do, if every passer by takes one look at my pretzels and asks, “Where’s the salt?”
Then I’m selling maybe 90% fewer pretzels, but wow! Look at the complements I get from those one or two people who appreciate the effort, but still don’t necessarily buy anything.
If three or four people out of one hundred are apt to complain about a detail like sodium, that the rest happily ignore, then keep the preferred recipe, and offer a separate low-sodium menu, optionally.
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.
So this is the part of evolutionary theory that can never really give up the ghost. There are non-deterministic/non-linear forces at work, which may or may not divulge direct evidence of sequential events.
Why did some primates emerge with brains twice the size of their ancestors, over many thousands of generations, during the course of several million years?
This hypothesis can only fit inside the huge knowledge gap. Many times, accelerated evolutionary changes signify arms races and bottle necks. An arms race like the Cambrian explosion has lots of things happening at the same time, a form of evolutionary tit-for-tat game. A bottle neck is something like the dinosaurs disappearing. The invasive species concept is, many times, kind of in between.
Since we can't access or develop a perfect map of primate migration patterns from an ideal fossil record of all historic skull sizes over time, demonstrating how the expanding brain case trend took shape, the details for the specific drivers of these changes are unclear.
We have a grand canyon sized void of information, and all we can really do is consider bridge designs that utilize natural forces to connect the empty space separating both sides. Figure, maybe, the stoned ape concept is like some epic beaver dam between us and our predecessors.
Since the human brain is an unprecedented organ, we have few avenues for corollaries. Like the big bang theory, we'll get stuck with whatever idea connects the most dots, fits inside the knowledge gap, whether it ousts other ideas or not.
Even if incorrect, the big bang fits what we see, but can never tell us why time started at all, if material existence truly began as a singularity, or whether something existed prior to moment zero. It may be that the big bang is an event that can only be obscuring prior information, due to some unknowable cosmological process that destroyed any such information predating this mysterious expansion event. Perhaps some crunch or freeze, reduced the sampleable scope of the universe we inhabit and currently observe into a pin-prick singularity we are forced to guess only broad, basic details about. How would we inform ourselves of what exists beyond the observable universe, or learn of events prior to a moment that destroyed all preceding facts or information?
As a hypothetical idea, the stoned ape hypothesis will always deal in uncertainty, at least until we discover the next ground-breaking evidence that changes the current picture. Same with the big bang: we can't really know if it's correct, so much as we can only deal in observable facts evident to our perspective, and that can be unsatisfying.
If multiple stories fit inside an evidence-starved narrative (brains doubling in size), these competing stories will sit deadlocked until a tie-breaker appears, usually with the most easily reasoned hypothesis carrying preference until rendered untenable. Science and institutional academia often shuns juicy excitement, which is where this theory's incredible story is found wanting of incredible evidence.
I think the Stoned Ape Hypothesis (sah) is reasonable within the context of a social lawlessness found in the state of nature. The chaos of the animal kingdom would permit the transgression of norms among primates, with little consequence, and it wouldn't matter as much for animals to be indulging in mind altering substances, if other needs were all essentially met by the surrounding environment.
Evolutionary theory is founded mostly on untouchable mechanics that operate at nearly geologic time scales, so we look, and we see slight incremental changes, and say to ourselves, yeah that holds up the rest.
But at it's core, the fundamental question is: Why did the human brain explode onto the scene? Why wasn't that change gradual? Why did it only happen once? Was there an accelerant in the mix?
To say that it happened fast is to speak in relative terms. It still would have happened across multiple generations, in movements of 10 and 20 years, according to sexual maturation. But to jump the rails, the change would have had to represent an ignition of sorts, to kick off a chain reaction that spreads outward from primary events, and is easily replicable crossing regional boundaries, once a successful game changer is cemented as viable.
The human brain isn't totally unique in it's structure, if you look at elephants and dolphins. But the relative brain size to body size ratio, as an emergent evolutionary trait, seems to be pretty unique.
Diet sounds like a plausible point of origin, when considering that the brain is a nutrition-greedy organ. So, the Stoned Ape Hypothesis is reasonable, in the sense that it layers nutritional augmentation on top of evolutionary theory. On the one hand, you still have evolutionary mechanics as the operating framework, but the dietary augmentation produces behavioral effects that change mating strategies.
So then, selection processes take over, and the successful live, and the others die. The successful produce alike offspring, and combinations of traits group together. But all clustered around this drug induced behavioral mess, where you find these apes getting into catnip and going nuts.
The idea is not without precedent. Consider the Greek Oracle, as a temple ventilated with toxic volcanic gases, acting as the mind altering substance. People willfully producing an altered state, by effectively huffing volatile, oxygen depriving vapors not unlike spray paint fumes, to gain insight and augment decision making.
Which brings us around to the crux of the idea. It should be possible to replicate the process, even at a small scale, by modeling the scenario with other animals. Usually mice have a short enough lifespan to push their genes around with careful engineering. So, what about talking mice that modify their environment? Could drugs and rampant sex make that happen in a time frame comparable to the fossile record for humans?
But geeze, talking mice that invent and implement conceptual ideas? What would we do with them, once they're here? What if they escape the lab? Would their population explode as an invasive species? Capable of direct lilliputian competition with humans?
Once the invasive species status is realized, all the rest fits into place. We wouldn't want to let the mice escape into the wild. So the only missing piece, regarding the mechanics of the idea, is the bridge in between dumb mice and smart mice.
The other is more about radiation hardening, and those are full, bulk duplicates of chromosome sets, like the hexaploid grain genome that was recently being discussed last week.
But I wonder when that sort of radiation hardening aspect was selected for? Millions of years ago? Billions of years ago? Or was it all just an accident, never selected for or even put to use? If we, as humans, only have a set from each parent, I’d estimate that bulk duplication doesn’t seem to offer real benefits in the radiation hardened sense, or everything would have more copies for billions of years.