FIGURE 12.1 Body-size distribution of mammals in North America. The black bars illustrate the distribution of species that went extinct in the QME. Note that humans are at the lower end of the distribution for species that went extinct. Illustration modified from Lyons et al. (2004); see that source for similar distributions of fauna from other continents.

as a whole (Fig. 12.1). Previous work has demonstrated that, as human biomass grows, the amount of solar energy and net primary productivity (NPP) available for use by other species shrinks, ultimately shrinking the amount of the world’s biomass accounted for by those non-human species (Vitousek et al., 1986; Maurer, 1996; Vitousek et al., 1997; McDaniel and Borton, 2002). Therefore, growth of human biomass should be inversely related to biomass of other species in general and to other megafauna species in particular, given that large body size itself to a large extent depends on available NPP. Such energetically driven biomass tradeoffs provide a new way to explore the QME and have the potential of extracting general principles relevant to understanding the future. That is the approach I take here, one that necessarily has many caveats (see Methods), but that nevertheless leads to some interesting observations.

Details of the QME and debates about its causes are summarized in recent reviews (Barnosky et al., 2004; Lyons et al., 2004; Koch and Barnosky, 2006; Wroe and Field, 2006). Salient points include the following. It was a time-transgressive extinction, beginning by 50 kyr B.P. in Australia and largely ending there by 32 kyr B.P., possibly concentrated in an interval between 50 and 40 kyr B.P. (Roberts et al., 2001; Trueman et al., 2005; Wroe and Field, 2006). In northern Eurasia and Beringia, extinctions were later and occurred in two pulses, the first between 48 and 23 kyr B.P. and the second mainly between 14 and 10 kyr B.P. (Koch and Barnosky, 2006), although some species lingered later in isolated regions (Irish elk until 7 kyr B.P. in central Siberia and mammoths until 3 kyr B.P. on Wrangel