[lithos]

Because of mass, the number of neurons, how many calories we can toss at them, and how many calories a fetus/newborn can be guaranteed.

Even if you have trainable brain, with neurons that can communicate with more percentage of the brain than a primates. You're still on a diet of hundreds of calories instead of thousands.

Looking at smaller animals cognitive abilities is newish. But does look like it will be going interesting places.