[JohnAaronNelson]

No one thinks the older structures are static. No one is arguing that. It's a simplified model about the origin.

This argument is akin to saying we're not "newer" apes ala

> The refutation is of the idea that it’s a strictly chronological ordering of species, with the old species still inside and intact. The correct view is that while homosapiens are indeed mostly "newer", the “older” apes were also modified throughout evolution

Obviously.

[theptip]

I mean… the quote from TFA that they are arguing against is

> As Paul MacLean (1964), originator of the triune-brain theory, stated,

>> man, it appears, has inherited essentially three brains. Frugal Nature in developing her paragon threw nothing away. The oldest of his brains is basically reptilian; the second has been inherited from lower mammals; and the third and newest brain is a late mammalian development which reaches a pinnacle in man and gives him his unique power of symbolic language.

And they quote other textbooks that are making claims along these lines too; this is right at the beginning of TFA. So I think you are wrong that “no one thinks that”.

Of course they don’t think the old brains are 100% static but there are claims that they are largely conserved.

[tigen]

MacLean doesn't say the brain is an onion with a tiny reptile inside!

[jacquesm]

> there are claims that they are largely conserved.

That they're not static doesn't necessarily mean that they aren't largely conserved.

[Retric]

It’s an incorrect and misleading model about the origin. Bat wings and bird wings share many traits but the common answer didn’t fly it’s simply convergent evolution. The brain structures of that same common ancestor is only vaguely related to modern structures in mammals and reptiles.

Modern reptiles, birds, and humans have experienced the same amount of evolution. There’s similar traits, but we don’t call whale flippers hands because that’s what the structures was in some of their ancestors or even what it is in related species. Similarly we don’t call human hands flippers because that’s what the structure started out as even further back and it’s still preforming that function in modern fish.

The human visual cortex is larger than most creatures entire brain, it’s a wildly different structure than you find on a frog which plays a wider role in cognition than just decoding vision.

[evv555]

Putting this particular theory aside the generalization that evolution is a nested hierarchy of structures is pretty obvious on the macroscopic level. Traits like breathing oxygen, having symmetrical bodies, backbones, limbs. These are all examples of structures building on top of one another sequentially and conserved across species. Sure each of these subcomponents continues to specialize but the core functionality remains largely the same.

Going back to your analogy saying visual cortex of frog is wildly different from a human visual cortex. That's similar to saying a frog backbone is wildly different from a human backbone. Sure that's true but there's also a shared common core functionality largely conserved across time

[Retric]

Again the issue is the theory is misleading. Those traits are conserved through evolution largely because they’re useful, but if you look at say owl skulls you find wild asymmetries because that’s more useful even our lungs are very different from each other. Hagfish lost backbones and snakes lost limbs because nothing is sacred to evolution.

So yes frogs and humans both have a visual cortex, because we both have eyes. It really doesn’t explain anything beyond that point. The human visual cortex doesn’t even map to the same structures as it expanded into nearby ones.

[evv555]

>It really doesn’t explain anything beyond that point.

I think taking a macroscopic view like this points at interesting types of analysis. Evolution is analogous to a hill climbing algorithm navigating towards local optima in a probability field. Macroscopic evolutionary trends give a low resolution peek into the underlying probability distributions.

[Retric]

That’s not what this theory is suggesting.

Frogs, birds, etc have very distinct spherical visual cortexes. Humans and squirrels don’t have that kind of spherical structure. So, other than naming where vision is processed the same thing the overlap isn’t particularly strong even at the most basic structural level.

It’s perfectly reasonable to extrapolate from studied organisms to species that share recent common ancestors. But reptiles don’t represent the probability distribution, they represent different results from that distribution under different evolutionary pressures. Extrapolation backwards and our common ancestor was very different from all decedents.

[aeternum]

But you could say that whale flippers are 'basically' their hands.

Every scientific model and analogy is flawed in some way, but many are still useful.

[Retric]

How exactly is this theory useful? Yes, frogs and humans process visual information because they both have eyes. That’s about all those structures have in common.

[aeternum]

For nearly all of human history everyone thought that those frog vs. human eyes were completely separate and designed by some magical being living up in the cloud.

By noticing that while they have significant differences, those structures also have significant similarities, we were able to correctly answer one of the greatest questions of all time: where did humans come from?

Of all models, this one is particularly useful.

[Retric]

To be useful models must accurately represent some aspect of reality, Reptiles don’t represent the brain of our common assessor particularly well. So this model is just wildly wrong without any predictive power.

Compare the giant spheres used by snakes, bird, frog etc to process visual information and try and map that to a rodent, bat, or human. Hint you’re not going to be able to locate an obvious sphere because the fundamental morphology is just different. You can say we both have areas of the brain devoted to processing vision but so do fruit flies.

[cma]

Eyes are a good example of conservation and path dependence, development is initiated by a fairly highly conserved gene:

https://en.wikipedia.org/wiki/PAX6#Species_distribution

[Retric]

Being reasonably conserved has minimal predictive power. Yes, knocking it or a closely related gene out out harms eye formation in a wide range of species but it says little about what specific structure ends up being formed.

[liquidpele]

> No one thinks the older structures are static.

It would seem enough people did to warrant this person to write about the topic.