Darwin’s Necessary Misfit and the Sloshing Bucket: The Evolutionary Biology of Emerging Infectious Diseases

Abstract

Evolutionary studies suggest that the potential for rapid emergence of novel host–parasite associations is a “built-in feature” of the complex phenomenon that is Darwinian evolution. The current Emerging Infectious Disease (EID) crisis is thus a new manifestation of an old and repeating phenomenon. There is evidence that previous episodes of global climate change and ecological perturba- tion, broadly defined, throughout earth history have been associated with environmental disruptions that produce episodic bursts of new host–parasite associations, each of which would have been called an EID at the time of its first appearance. This perspective implies that there are many evolutionary accidents waiting to happen, requiring only the catalyst of climate change, species introductions, and the intrusion of humans into areas they have never inhabited before.