Paleontologist David Raup noted that
The disturbing reality is that for none of the thousands of well-documented extinctions in the geologic past do we have a solid explanation of why the extinction occurred. We have many proposals in specific cases, of course: … These are all plausible scenarios, but no matter how plausible, they cannot be shown to be true beyond reasonable doubt. Equally plausible alternative scenarios can be invented with ease, and none has predictive power in the sense that it can show a priori that a given species or anatomical type was destined to go extinct. (David M. Raup, Extinction: Bad Genes or Bad Luck? (New York: W.W. Norton, 1991), p. 17.)
Recently, two paleontologists Charles Marshall of UC Berkeley Museum of Paleontology and post-doctoral fellow Tiago Quental have possibly added to the list by offering “failure to evolve” in relation to the environment as a cause. Or, as the Red Queen put it in Through the Looking-Glass, “it takes all the running you can do, to keep in the same place.”:
“Virtually no biologist thinks about the failure to originate as being a major factor in the long term causes of extinction,” said Charles Marshall, director of the UC Berkeley Museum of Paleontology and professor of integrative biology, and co-author of the report. “But we found that a decrease in the origin of new species is just as important as increased extinction rate in driving mammals to extinction.”
The results, published June 20 in the journal Science Express, come from a study of 19 groups of mammals that either are extinct or, in the case of horses, elephants, rhinos and others, are in decline from a past peak in diversity. All are richly represented in the fossil record and had their origins sometime in the last 66 million years, during the Cenozoic Era.
Though the specific cause of declining originations and rising extinctions for these groups is unclear, the researchers concluded that the mammals’ death was not just dumb luck. “Each group has either lost, or is losing, to an increasingly difficult environment,” Marshall said. “These groups’ demise was at least in part due to loss to the Red Queen — that is, a failure to keep pace with a deteriorating environment.”
Deteriorating, that is, for them. What was good for trees wasn’t good for buffalo, and versa vice.
One good thing about these guys’ hypothesis is that it is testable today (not like “What really happened to the dinosaurs?”). We can follow serious declines in populations, where the decline is caused by changing environment rather than human action, and see what actually happens to those members of a species not kept alive in wildlife preserves.