How to Test the Cosmic Zoo Hypothesis

Abstract

At the start of this book we introduced the idea that complex life evolved from simple life in a number of key steps or innovations. Our hypothesis is that all the steps in this progression have happened many times on Earth, and so are likely to occur on other worlds. In Part II of this book, we found that most of those transitions are likely Many Paths events. If the history of the Earth were played out again, the tape rewound, the same key innovations would arise, not necessarily incorporating the same biochemistry or anatomy, but providing the same functionality. So if life arises on a distant exoplanet, it will also traverse the path from simple to complex, unicellular to multicellular, and produce intelligent animals capable of tool use in its forests and kelp beds, providing the planet is habitable for long enough.