Is there any explanation why we have two brain hemispheres? Is there any advantage of having two in contrast to having one (or three / four)?
From what I've read so far (not too much; I'm not a biologist) each half can take the job of the other half when it comes to injuries. Is that correct?
Are there animals which have more than two hemispheres?
edit: I have seen What was the evolutionary reason for cross lateralization of the brain?, but that question seems to be about the question why the left hemisphere controls right body parts and the right hemisphere controls left body parts. My question is why there are two hemispheres at all.