Bruce continues to consider what our best theories tell us about knowledge. Is there something special (or even physically different) about the knowledge created by nature through biological evolution and human minds (i.e. the 'two sources hypothesis')? How should we think about knowledge created in human minds that could take us to the moon and beyond or divert an asteroid? Is it physically different from the kind of adapted information created by animals or the immune system? Or does it merely a broader and deeper search for solutions?

Along the way, he delves into machine learning, animal behavior, the immune system, trade secrets, robots, and many other concepts related to David Deutsch’s ideas about knowledge but are outside the 'two sources' and thus not considered 'knowledge' by David Deutsch.