It's mentioned offhandedly in this NYTimes article about echidnas that their brains are 50% neocortex, which presumably is a lot (human brains are 30% neocortex). They also call them "brainy," and say they're surprisingly intelligent. Wikipedia says "a high neocortex ratio is thought to correlate with a number of social variables such as group size and the complexity of social mating behaviors" (unreferenced). What significance does it have? How unusual is a ratio of 50%? What are the odds that echidnas secretly rule the world?

I thought only mammals were conventionally considered to have a "neocortex." That might not be a homologous structure in echinoderms.

Um, that's echidnas, not echinoderms! They are mammals, albeit bizarre ones.

Um, that's echidnas, not echinoderms! They are mammals, albeit bizarre ones.

 

Ohh. Sorry. I read that rather uncarefully.

 

Well. Maybe neocortex ratios get larger with smaller brain size. I don't really know. Monotremes might not follow the regular mammals rules as well, either.

The short answer is that for each (let's call it a) joule of energy invested in the brain, that much more of it is devoted to higher thinking... stuff like math, abstraction, musculo-skeletal control, perception (vision, scent, touch, etc.), and basic problem solving.

 

Less neocortex tends to mean more of that energy delivered to the brain is ultimately devoted to simple stuff like breathing, heartrate, and baser emotions, which implies poor efficiency.

 

With a higher percentage of neocortex, each unit of energy delivered to the brain is spent more wisely. <snicker>

Part of the problem is assessing species intelligence. What's a fair test across species, one that won't be biased by a particular species' or group's life history, habitat, etc? How well does this fair test reflect "intelligence"?

 

And how much does neocortex matter? Do mammals just "centralize & specialize", while other organisms like birds and reptiles have the relevant neurons spread widely in the brain?

 

It's tantalizing and interesting, but we shouldn't jump to conclusions just yet.