We have examined the more than 3 billion year history of life on earth, and the great diversity that has come about as a consequence of that history. Tens of millions of species share the planet earth, all different, yet all apparently arising from a single common ancestor, and all easily categorized into just a few dozen common evolutionary themes. We learned that each species is dependent on the functioning of the ecosystems in which it lives, and especially on the environment to which it has become adapted, and that each species can influence the fate of many other species in its ecological community. Finally, we have examined the impact of human actions on the intricate fabric of life on earth, and how this single species is radically altering the biosphere. Simple forms of life arose under conditions very different from the present day, ultimately reshaping the physical environment.
Natural selection operating on genetic variation leads to adaptation and diversification.
The ultimate source of variation is random mutation. Speciation results from the evolution of any differences that keep groups of populations reprodu ctively isolated from one another. Models of these systems can often be used to help understand and predict how the interactions between components will influence outcomes. Perturbation experiments are useful tools to test our understanding. They often result from treating natural resources as a commons, they are exacerbated by rapid population growth, new technological advances, and rampant consumption of resources.