Your brain is built of cells called neurons and glia—hundreds of billions of them. Each one of them is as complex as a city. . . . The cells [neurons] are connected in a network of such staggering complexity that it bankrupts human language and necessitates new strains of mathematics. A typical neuron makes about ten thousand connections to neighboring neurons. Given billions of neurons, this means that there are as many connections in a single cubic centimeter of brain tissue as there are stars in the Milky Way galaxy.

When we are born our brains are preprogrammed with learning accumulated over hundreds of millions of years. For example, researchers at the University of Virginia have shown that while many people have an instinctual fear of snakes, no one has an instinctual fear of flowers. The brains that we were born with had learned that snakes are dangerous and flowers are not. There’s a reason for that.

There is one grand design for the brains of all mammals, fish, birds, amphibians, and reptiles, which was established nearly 300 million years ago and has been evolving ever since. Just as cars have evolved into different versions—sedans, SUVs, sports cars, etc.—that rely on many of the same underlying parts, all vertebrate brains have similar parts that do similar things but that are well adapted to the needs of their own particular species. For example, birds have superior occipital lobes because they need to spot prey (and predators) from great heights. While we humans think of ourselves as superior overall because we overemphasize the importance of our own advantages, other species could justifiably make the same claims on their own behalf—birds for flight, eyesight, and instinctual magnetic navigation; most animals for smell; and several for appearing to have particularly enjoyable sex.
