The reason that people have brains is that they are worms. This is not a value judgment but a biological observation. Some animals, such as jellyfish and sea urchins, are radially symmetrical. Others are bilaterally symmetrical, which means they are long, thin and have heads. Headless animals have no need for brains. But in those with a head the nerve cells responsible for it-and thus for sensing and feeding-tend to boss the others around. That still happens even when a long, thin animal evolves limbs and a skeleton. Bilateralism equals braininess.
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