When you get a moment, check out How a Fly Flies, it's a TED talk by Michael Dickinson that talks about how evolved a fly is. Brain size and function has a lot to do with it. It sure does take a lot of energy to run our brains, hopefully we can use them to keep the Chimp insurgence at bay.Surprisingly, even though we have to fuel a massive thinking organ we don’t use more energy than a chimp; whose piddly little brain is only ¼ the size of ours (which will make it more embarrassing when they take over the world).
First of all, I laughed out loud when I read that.
That is a rather interesting talk. When you look at mammal brains they all have a very similar structure. The human brain, for all intents and purposes, is just an enlarged chimp brain. So it's easy to forget that other groups are just plain freaky in the neuron department.
As a general rule brain size relative to body size is a good predictor of intelligence, although other measures can be better in different lineages. For example, primates have a high neuron density thus absolute brain size is a good predictor of intelligence amongst them. This high neuronal density also means that humans - despite not having the biggest brains - appear to have the most neurons of any animal.