This book is really important. The study of how micro-evolution happens from one year to the next to the next in the Galapagos gave me a lot of insight into how the environment shapes species. Traits are constantly changing, yet the graph jitters back and forth around some more-or-less average value. It's really not average, though, because climate, rainfall, etc. are all fundamentally chaotic systems. Organisms tend to track generation by generation the conditions as they fall out. Over geologic time that can either result in vast changes or effective stasis, depending on the situation. It's cool to picture how macro-evolution happens as a result of thousands of years of micro-evolution.