Page 301 - Environment: The Science Behind the Stories

If current trends continue, the modern era, known as the
Quaternary period, may see the extinction of more than half
of all species. Although similar in scale to previous mass
extinctions, today’s ongoing mass extinction is different in
two primary respects. First, we are causing it. Second, we will
suffer as a result.

We are setting the sixth mass
extinction in motion

In the past few centuries alone, we have recorded hundreds
of instances of species extinction caused by people. Sailors
documented the extinction of the dodo on the Indian Ocean
island of Mauritius in the 17th century, for example, and today
only a few body parts of this unique bird remain in museums.
Among North American birds in the past two centuries, we
have driven into extinction the Carolina parakeet, great auk,
Figure 11.7 The ivory-billed woodpecker was one of North Labrador duck, passenger pigeon (p. 80), almost certainly the
America’s most majestic birds. It lived in old-growth forests
throughout the southeastern United States. Forest clearing and Bachman’s warbler and Eskimo curlew, and likely the ivory-
timber harvesting eliminated the mature trees it needed for food, billed woodpecker (Figure 11.7). Several more species, includ-
shelter, and nesting, and this symbol of the South appeared to ing the whooping crane, Kirtland’s warbler, and California
go extinct. In recent years, fleeting, controversial observations condor (pp. 315–316), teeter on the brink of extinction.
in Arkansas, Louisiana, and Florida have raised hopes that the However, people may have been hunting species to
species persists, but proof has been elusive. extinction for thousands of years. Archaeological evidence
shows that in case after case, a wave of extinction followed
close on the heels of human arrival on islands and continents
(Figure 11.8). After Polynesians reached Hawaii, half its birds

Eurasia
>30,000 yr ago North America
36% of large mammal genera ~10,000–11,500 yr ago
72% of large mammal genera

?
Pacific Islands
~1000–3000 yr ago Africa
50+% of endemic ~160,000 yr ago
landbird species 18% of large mammal genera

?

South America
Australia ~10,000–15,000 yr ago
~44,000–72,000 yr ago 83% of large mammal genera
88% of large Madagascar
mammal genera ~1500 yr ago
New Zealand lemurs,
~1000 yr ago elephant birds, others
moas, other birds

Figure 11.8 This map shows when humans arrived in each region, and the extent of extinctions that
followed. One extinct animal from each region is illustrated. Larger human hunter icons indicate more evidence
and certainty that hunting (as opposed to climate change or other factors) was a primary cause of extinctions.
Data for South America and Africa are so far too sparse to be conclusive. Adapted from Barnosky, A.D., et al., 2004.
Assessing the causes of late Pleistocene extinctions on the continents. Science 306: 70–75; and Wilson, E.O., 1992. The diversity of
300 life. Cambridge, MA: Belknap Press.

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