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.
Solutions require global cooperation and sacrifice, and the development of an environmental ethic.