Des Collins studies the fossils of the Burgess Shale that represent the Cambrian Explosion of animal life. An animation of this event shows the transition from the simple animals that existed before the explosion to the many complex, weird forms that evolved in a geological blink of the eye.
Rudy Raff presents several theories to explain what caused the explosion. By the end of the explosion, all 35 of the present groups or phyla of animals existed and no new ones have evolved since. Nature had evolved life’s essential designs in a single evolutionary leap. Every new shape of life that has followed has been a variation on one of these themes or phyla.