PANZOOTICS, PARSIMONY, AND PALEONTOLOGY: CAN DISEASE CAUSE EXTINCTION?

During the late Quaternary, mammalian faunas were affected almost worldwide by an unusual series of extinctions that were highly regionalized and temporally disjunct. Thus, about 11,000 bp in the Americas 130+ species (including mammoths, mastodonts, “ground” sloths, sabertoothed cats, and many others) disappeared very suddenly, perhaps in the space of 400 yr. Similar but smaller losses occurred in Australia/New Guinea ~ 50,000 bp, in the West Indies ~ 5000 bp, and in Madagascar ~ 1000 bp. These extinctions are widely believed to have been anthropogenic in nature, and thus represent the “first” biodiversity crisis forced by our species. But what is the evidence for this conclusion? Overhunting is frequently mentioned as the leading cause, but for several reasons it is highly improbable that primitive peoples could have induced so many species losses in this way. Climate change is even more unlikely. As an alternative, I propose that most features of late Quaternary extinctions can be explained by inferring that the principal agency of loss was infectious diseases introduced into immunologically naive populations by colonizing humans or their commensals/synanthropics. The “hyperdisease hypothesis” potentially (1) explains differential losses in K-selected vs. r-selected taxa (both young and old animals highly susceptible to disease, causing catastrophic depression in rate of natural increase in larger taxa); (2) requires no ad hoc explanations for the absence of mass kill sites in affected areas (mass kill sites absent because losses attributable to human hunting were usually negligible); and (3) accounts for pattern change in the character of anthropogenic extinction after first-contact losses. Recent successes in utilizing “ancient DNA” techniques for recovering evidence of viruses in fossils will be discussed.