The Worm In Your Brain

One of the most fascinating things about the history of life is the way distantly related species can look alike. In some cases, the similarities are superficial, and in other cases they are signs of a common ancestry. And sometimes--as in the case of our brain and the brains of worms--it's a little of both. The biggest feature of our brains is a massive stack of densely woven neurons called the cerebral cortex. Once our brains take in sensory information, it's the cortex that integrates it, makes sense of it, learns from it, and decides how to respond. If you compare our cortex to those of our close relatives, the apes, they're nearly identical in structure, although our cortex is very big for our body size. If you look further afield, you'll find the same basic architecture of the cortex in all vertebrates, although different parts are different size in different species. Because these similarities are so consistent in so many different ways, and because you can trace the changes to the cortex along different lines of descent, they're strong evidence that the common ancestor of all vertebrates had a cortex.