Introduction

Diversity and evolutionary innovation are the hallmarks of life. Life appears to defy the laws of physics and chemistry and it does so with the help of energy. Life succeeds by finding ways to overcome natural and physical hindrances. Life spread over the face of the globe and filled almost every crevice and habitat. Of course there are limits to what evolution can do. Everything is not possible. For example, there must be a limit to how tall California redwoods can grow just as there must have been a limit to the size of dinosaurs. Although life's success appears almost boundless and has had continued success for more than four billion years, there are no general laws describing the limits of evolution. This is in contrast to physical and chemical laws that define constraining limits. The grandest experiment of nature, the evolution of life, has no theory equivalent to E = mc2.

The basic forces of evolution, both intrinsic (mutation, migration, sexuality, selection, and random genetic drift) and extrinsic (historical contingency and major catastrophe), generate not a single outcome but a range of possibilities.