Environmental Engineering Reference
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They used genetic proi ling of coprolites from Oregon to demonstrate a human
presence in North America at least 1,000 years before the Clovis complex, a dating
that would extend the blitzkrieg period to more than 2,000 years. The latest, and
a very convincing, demonstration of pre-Clovis hunting comes from a projectile
point made of mastodon bone and embedded in a rib of a disarticulated mastodon
found in Washington state: Waters et al. (2011) dated the point to 13,800 years ago,
proving that hunters were killing proboscidean megafauna at least two millennia
before Clovis. Even before these latest i ndings, Grayson and Meltzer (2003) offered
their requiem for North American overkill—but Fiedel and Haynes (2004) called
their conclusions “a premature burial.”
Arguments often hinge on the accuracy of stratigraphic interpretation, geochem-
istry, and radiocarbon dating. Australia's megafaunal extinctions are a perfect illus-
tration of these disagreements. Miller et al. (2005) analyzed isotopic tracers of diet
preserved in eggshell and teeth to conclude that the megafaunal habitat, a mosaic
of drought-adapted trees, shrubs, and grasslands, was converted by i res set by
humans to today's i re-adapted desert scrub shortly after the continent's human
colonization, some 50,000 years ago. This blitzkrieg story was questioned by
Trueman et al. (2005), whose dating of Cuddie Springs deposits demonstrated a
prolonged coexistence (for a minimum of 15,000 years) of humans and the now
extinct megafauna. But Gillespie (2008) claimed that the latest dating shows that
the Australian evidence i ts the overkill pattern, and Grün et al. (2009) explained
that Trueman et al. (2005) were misled by a l awed geochemical argument and that
a correct redating of the Cuddie Springs fossils puts their age at 51,000-40,000
years before the present, or within the interval that matches the last megafaunal
survivals in other parts of Australia.
On the other hand, closer examinations of some of the seemingly convincing
overkill explanations show that they often err by generalizing on the basis of limited
(or questionable) evidence or by relying too much on theoretical models based on
questionable assumptions. Barnosky (2008) identii ed “megafauna biomass trad-
eoff” (including humans as a megafauna species) as a driver of Pleistocene (and
future) extinctions, and even quantii ed the process for the past 100,000 years. His
conclusion: until about 12,000 years ago, the loss of animal megafauna largely
matched the growth of human biomass, and after the megafaunal crash the global
system gradually recovered to its precrash level, but with the megafaunal biomass
concentrated in a single species, Homo sapiens .
Given our poor understanding of both zoomass densities and hominin numbers
during the past 100,000 or even 10,000 years such an exercise is merely a
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