Mass Extinction

A majority of the nation's biologists are convinced that a "mass extinction" of plants and animals is underway that poses a major threat to humans in the next century, yet most Americans are only dimly aware of the problem, a poll says.

The rapid disappearance of species was ranked as one of the planet's gravest environmental worries, surpassing pollution, global warming and the thinning of the ozone layer, according to the survey of 400 scientists commissioned by New York's American Museum of Natural History.

The idea of individual species becoming extinct is quite familiar; indeed it is a rather sad indictment of our stewardship of the planet that we are all too familiar with extinction. But, in fact, extinction is a rather complex phenomenon. At one end of the continuum we have the notion of a population of organisms evolving into something else. Here, the disappearance of the original phenotype might be accomplished by nothing more than natural turn-over of the generations (anagenesis).

At the opposite end of the spectrum, we have the mass extinctions, where huge proportions of the earth's biota disappear more or less simultaneously, within an interval that is, in some sense, short. At least some of the more sensational explanations for these phenomena require the wholesale killing of individual organisms. Between these two extremes we have a range of possibilities, further complicated by the vagaries of the fossil record and our imperfect interpretation thereof. And always, even in the case of the KT event which cannot be "explained away" in its entirety by meteorite impact, there is the enigma of underlying cause.