The fate of biological diversity for the next 10 million years will almost certainly be determined during the next 50–100 years by the activities of a single species. That species, Homo sapiens, is ≈200,000 years old. It has been fabulously successful by ecological standards: it boasts as-yet-unchecked population growth and a cosmopolitan distribution, and it has vanquished its predators, competitors, and some of its parasites. The fossil record suggests that the typical mammal species persists for approximately one million years (Martin, 1993), which puts Homo sapiens in mid-adolescence. This is a fitting coincidence, because Homo sapiens is now behaving in ways reminiscent of a spoiled teenager. Narcissistic and presupposing our own immortality, we mistreat the ecosystems that produced us and support us, mindless of the consequences.

The state of biodiversity today is a reflection of that abuse, but the reflection is hazy because we know neither the total number of populations or species nor how many have gone extinct. Our best information is on the rate and extent of habitat destruction and degradation. For example, we know from long-term monitoring that coral cover in Jamaican reef ecosystems declined from >50% to <5% between the late 1970s and 1994 (Hughes, 1994). From remote-sensing studies, we know that the rate of selective logging in the Brazilian Amazon ranged from 12,000 to 20,000 km²/year between 1999 and 2002 (Asner et al., 2005) and that the rate of deforestation in the Peruvian Amazon averaged 645 km²/year from 1999 to 2005 (Oliveira et al., 2007). Likewise, we know from global mapping studies that nearly 50% of all temperate grasslands, tropical dry forests, and temperate broadleaf forests have been converted to human-dominated uses worldwide, whereas only 4–10% of those biome types are formally protected (Hoekstra et al., 2005).

Of the total number of species on Earth, we still cannot say much more than that it is likely to be “of the general order of 10⁷” (May, 1988). Estimates of species extinction rates—often based on estimates of habitat loss in conjunction with the species–area relationship—are similarly imprecise (May et al., 1995; Balmford et al., 2003b) and are sensitive to multiple assumptions [e.g., Regan et al. (2001) and Seabloom et al. (2002)]. The number of animal and plant extinctions certified since 1600 is only slightly greater than 1,000 (May et al., 1995), but our pitiful knowledge of biodiversity’s extent and the inherently inconspicuous nature of extinction ensures that this figure is a small fraction of the true number. Although no scientific consensus is forthcoming on the exact rate of extinction for any region or group of organisms, much less for global biodiversity, there is