What Are Different Brains Made Of?

The brain is the most complex organ that ever evolved. The brain controls important functions in the body like keeping your heartbeat and your breathing normal. It controls the movement of your eyes across the page as you read this, it makes sense of the ink on the page to form words, and it links these words with concepts in your memory and makes new concepts as you learn. And the brain was also the part of your body that made the decision to read this article in the first place. In different animals, brains are very different. There are large and small brains, smooth and wrinkled brains, brains with some parts larger than others. How are these brains built? How did they come to be so different from each other—and why does that matter?