In several past entries, I have referred to the ongoing revolt in the archaeological community against the Clovis Horizon – the theory that there were no human beings in the Americas before the Clovis culture of 11,500 BCE (13.5 thousand years ago). Andrew Curry, writing in the May 2, 2012 issue of Nature, reports on some new developments in the campaign against "King Clovis." In Oregon, Dennis Jenkins has dated fossilized human excrement, or coprolites, to sometime between 14,300 and 14,000 years BP (Before Present). In neighboring Washington state, a 14,000-year-old site containing mastodon remains also yielded evidence of human activity, in the form of a probable projectile point made from the bones of another mastodon. In Texas, archaeologists found tools that were 1,000 years older than the earliest Clovis artifacts. Some of these findings were actually made in the 1980s, before scholars began seriously to question the Clovis Horizon, but as is so often the case with a scientific paradigm, archaeologists ignored evidence that didn't fit the model.
Meanwhile, a mitochondrial DNA study by Ripan Malhi of the University of Illinois suggests that the ancestors of the first paleo-Indians might have spent as much as 5,000 years hanging out in Beringia (the now-submerged Bering Strait land bridge) before following the coast or traversing the glaciers southward. If true, this would place the first humans in the Western Hemisphere as early as 21,500 years BP. Brian Kemp, one of the scholars studying On Your Knees Cave Man, counters with DNA mutation-rate data that place a 16,500-year limit on migration to the Americans. Both dates, of course, are considerably older than the Clovis boundary.
Finally, the hypothesis that the earliest Americans included seafarers has been bolstered by a 2008 study identifying several species of seaweed at Tom Dillhay's Monte Verde site in Chile, and by a 2011 article "demonstrat[ing]" human habitation in the Channel Islands of California 12,000 years ago. The Clovis Horizon, in sum, is collapsing under the weight of many humble pieces of data: bone fragments, tool shards, seaweed, and poo.