Um, where do you keep your gizzard stones then?

Because the brain physically, anatomically, has these "old strata". Lizard brains are pretty much just a basal ganglia. Humans have a basal ganglia, and then extra stuff on top. Mammals, and only mammals, have a neocortex "strata" to their brain as well.

I am not qualified to argue for or against the Triune brain, but it seems easy to see why the brain is different from the stomach in this regard.

In addition to this... Sure, evolution modifies existing structures, but if you compare a cat's heart and stomach to a pig heart and stomach, the difference is not that big, even though the nearest evolutionary ancestor was tens (hundreds?) of millions of years ago. Once a structure is in place and works well, you can certainly tweak it, but it's easier to mostly just keep it.

Humans have a neocortex, but if you play with a cat or dog, you can recognize and understand the emotions they are feeling. Fear, anger, joy, anxiety, relaxation, etc. That suggests the structures responsible for those things in us are probably not that different from them.

> Humans have a neocortex, but if you play with a cat or dog, you can recognize and understand the emotions they are feeling. Fear, anger, joy, anxiety, relaxation, etc. That suggests the structures responsible for those things in us are probably not that different from them.

And yet birds don't have a neocortex, and yet they share all the same behaviors that mammals share (at least in some species). I don't know if there is some creature with a neocortex that doesn't share all of these behaviors, but at least we can see that the neocortex may be sufficient but is not required for a species to have them.

> Because the brain physically, anatomically, has these "old strata". [...] Humans have a basal ganglia, and then extra stuff on top.

IMO the key is distinguishing between these two ideas:

1. There is a gross anatomical structure that can be linked to ancient ancestors with certain characteristics.

2. Those structures in living creatures are somehow "not really modern" or are unusually tied to the needs or limitations of those ancient ancestors.

Consider your fingers: They originate from fin-bones ~380 million years ago, yet (unlike "lizard brain") nobody talks about possessing "fish fingers" except as a fried food product. We also don't create narratives explaining our finger operations or design in terms of what ancient fish required or were capable of.

The Pterodactylus flying lizards are named literally for their "winged fingers". I suspect that we talk about this stuff when discussing evolutionary biology just fine, it's just that the "lizard brain" is a popsci term that the great-unwashed have latched onto.

Agreed. Mammals don’t even have the same metabolic strategy as reptiles - we’re endothermic while reptiles can’t even self regulate body temperature. Other systems fundamental to life like our reproductive strategies are also completely different.

The idea that major organs are strictly conserved over 250 million years while something as fundamental as homeostasis drastically diverges is frankly a bit wackadoo.