“imagine yourself on one goal line of a football field. That line represents the first fossil, a microscopic, single-celled organism. Now start marching down the field. You pass the twenty-yard line, the forty-yard line, you pass midfield, and you’re approaching the other goal line. All you’ve seen this entire time are these microscopic, single-celled organisms. “You come to the sixteen-yard line on the far end of the field, and now you see these sponges and maybe some jellyfish and worms. Then — boom! — in the space of a single stride, all these other forms of animals suddenly appear.
