As we reach the end of our safari, we come to see that this book was really about ourselves all along, albeit as seen through the prism of our colorful cousins across the animal kingdom. By surveying the spectrum of animals living today we have glimpsed what became of those humble little urbilaterians who roamed the Precambrian seas ~600 million years ago. Their external anatomy has diversified enormously, but their genome has not. It persists as the operating system for most of the animal world. We are only beginning to understand the quirky “apps” that make one species different from another.

The winding path from urbilaterians to our own species has been as multifarious as our tour of the animal kingdom. Over the eons, our ancestors were nudged from one ecological niche to another by forces both large (e.g., tectonic plates shifting and meteors hitting the earth) and small (e.g., food availability and sexual selection). These forces reshaped us from fish to amphibian to reptile and eventually to our present form, occupying the place in morphospace that we affectionately call Homo sapiens. But all of those forces were beyond our control, and none of them was unique to our lineage. The same can be said, essentially, for every other species on earth. If there is one lesson from this book that stands out above the rest, therefore, it is this: Contingency rules destiny.