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Tuesday, March 29, 2005

The Amateur Organismal Biologist

Why do reptiles have smaller brains for their body size than mammals ?
This is a clear pattern. I'm sure all reasonable explanations have been considered.
I thought of one. A key problem for cold blooded animals is that they're nerves work slowly in the cold. They become sluggish. This is very costly especially if they are cometing with warm blooded animals at night or in the early morning

This could make it very important for reptiles to have short reflex arcs (did I use the term correctly well anyway I explain). Consider sensory stimulus goes in and behavior comes out. In the simplest case only two nerves need to be involved sensory in motor out. In this case (me blogging) many neurons are involved. Now imagine how long it would take me if each synapse worked slowly because I was cold blooded and cold.

A large brain might be a disadvantage for a coold reptile. It would still be slowly slowly figuring out how to respond long after it was in the stomach of a mammal.

Now consider relatively large reptile brains. They are found in large reptiles which are found in areas with very even temperature. Also large reptiles tend to be alligators and crocodiles who are generally found in the water (evens out temperature swings). Now their brain sure isn't huge, but there is nothing more sluggish than an alligator in an ice box (except maybe me).

Also comodo dragons live on evenly warm islands and Galapogos turtles live on islands almost exactly on the equator (also there are huge land iguanas on the Galapogos).

In contrast small lizards and snakes manage to be pretty alert even in fairly early spring in temperate zones.

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