We love origin stories. When we see successful groups of animals and plants, we wonder where they came from, and how they rose to power. How did the tetrapods—the group of four-legged animals that we belong to—start walking on land? What made the insects the most diverse group of animals on the planet? Why did flowering plants suddenly start diversifying during the Cretaceous period, filling the world with blossoms?

These enduring questions are so fundamental to biology that we sometimes forget how strongly they’re influenced by the limits of our senses. We can see the creatures they concern with our naked eyes. We can observe changes in their bodies, and we can tell that they must have gone through transformations from