THE GEOLOGICAL CONSEQUENCES OF EVOLUTION

James Hutton, son of the Edinburgh Enlightenment, conceived of our planet as a superorganism sustained by global metabolism, in part biological. Nearly two centuries later, James Lovelock revisited Hutton’s conception, coining the term “geophysiology” for the explicitly biological regulation of the Earth system. Because of evolution, the biota has changed through time. Does it follow, then, that evolution constitutes a principal engine of secular change in Earth surface environments?

Paleontologists generally focus on the evolution of morphology, but in terms of Earth system science, it is physiology that matters. Great physiological innovations have been few, and most occurred during early in Earth history. Despite this, environments have continued to change throughout Earth history. This suggests that while evolution may define the geobiological potential of organisms, major historical changes in the Earth system must reflect physical as well as biological influences. Indeed, evolutionary change is probably modulated by physical processes at least as much as the reverse.

Evolution may not provide a simple explanation for long term environmental change, but as Lovelock recognized, population biology may help us to understand the opposite phenomenon -- how environments maintain homeostasis over long time intervals. Evolutionary theory predicts that populations will evolve to maximize fitness. As understood by biologists, fitness is not global or absolute. It is local and immediate, and is defined relative to other populations with similar metabolic needs and physiological capabilities. By altering their local environment, then, populations may decrease their own fitness. For this reason, stabilizing selection will reflect, at least in part, geophysiological feedbacks that maintain the environmental status quo.

Humans are different. Unlike other organisms, we have not adapted to local conditions, but rather altered environments to suit our physiology. The result is a modulation of the Earth system whose scope we do not yet fully understand. The consequences, however, are likely to alter evolution as well as environments.