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Holocene extinction event

The Holocene extinction event is the widespread, ongoing extinction of species occurring in the modern Holocene epoch. The current extinction event may be downplayed by the traditional separation of 'Recent' (Holocene) time from the Pleistocene, or 'Ice Age' extinctions, exemplified in popular imagination by the extinction of the woolly mammoth and the Neanderthal people. Modern climatology suggests that the 'Holocene' epoch we live in is no more than the latest in a series of interglacial intervals between glaciation events, one that will perhaps become artificially extended by global warming.

The rate of extinction today appears to be similar to, or perhaps greater than, the rate during the five "classic" extinction events in deep geological time, such as the Permian extinction that extinguished some 90 percent of the Paleozoic biota, or the dramatic extinction event that eliminated all dinosaurs except birds at the end of the Cretaceous, 65 mya.

The coincidence between the appearance of modern humans and the extermination of large mammalian Ice Age biota ('megafauna') requires explaining. The 'prehistoric overkill' hypothesis of Pleistocene extinctions has been especially clearly formulated by Paul S. Martin, University of Arizona. The culture that has been connected with the wave of extinctions in North America is the paleo-Indian culture associated with the Clovis people (q.v.). Not everywhere is the 'Great Hunt' of the Pleistocene or 'prehistoric overkill' hypothesis confirmed. For instance, the timing of sudden megafaunal extinctions of large Australian marsupials and a giant lizard, events that followed the arrival of human beings in Australia by many thousand years, need examining. It is often noted by biologists that there have not been such sudden extinctions on a comparable scale in Africa either, where the fauna evolved with hominids; post-glacial megafaunal extinctions in Africa have been spaced over a longer interval.

Megafaunal extinctions include

In Europe: (ca 15,000 years Before Present)

In North America: (ca 12,000-9000 years BP), 35 to 40 species of large mammals (and only about half a dozen small mammals, such as mice and rats) disappeared. Previous North American extinction pulses had occurred at the end of glaciations, but not with such an imbalance between large mammals and small ones. The megafaunal extinctions include twelve genera of edible grazers (G), and five large, dangerous carnivores (C). North American extinctions included

The survivors are as significant as the losses: Bison, Moose (recent immigrants through Beringia), Wapiti (Elk), Caribou, Deer, Pronghorn, Muskox, Bighorn Sheep, Mountain Goat. All save the Pronghorns descended from Asian ancestors that had accommodated with human predators. This connection has recently been expanded upon and supported in detail by R. D. E. MacPhee, Extinctions in Neartime, 1999, an outgrowth of an American Museum of Natural History conference on extinctions, 1997.

The chief opposition to the 'prehistoric overkill' hypothesis has been that population of humans such as the Clovis culture were too small to be ecologically significant. Other generalized evocations of climate change fail under detailed scrutiny.

Reference: E. C. Pielou, After the Ice Age: the return of life to glaciated North America, 1991

In South America, which had remained largely unglaciated, except for increased mountain glaciation in the Andes, there was a contemporaneous but smaller wave of extinctions.

In Australia: (ca. 26000-15000 BP) the sudden spate of extinctions came earlier than in the Americas, but lagged well after the first entry of humans. The Australian extinctions included:

Some extinct megafauna, such as the bunyip-like diprotodon, may be the sources of ancient cryptozoological legends.

Such megafaunal extinctions have continued to the present day. Modern extinctions are more directly attributable to human influences. Extinction rates are minimized in the popular imagination by the survival of captive trophy populations of animals that are merely "extinct in the wild," (Père David's Deer, etc) and by marginal survivals of highly-publicized megafauna that is "ecologically extinct" (Giant Panda, Sumatran Rhinoceros, the North American Black-Footed Ferret, etc.). Some notable examples of modern extinctions of "charismatic" mammal and bird fauna:

Most ecologists associate the current high extinction rate with human activities, directly or indirectly. There still is debate as to the extent to which the disappearance of megafauna at the end of the last ice age can also be attributed to human activities, directly by hunting or indirectly, by decimation of prey populations. While climate change is still cited as an important factor, such anthropogenic explanations have become predominant.

Although a scientific consensus has been won, that current extinction rates are above the ordinary averages of 'background extinctions', there is still much journalistic debate about the likely extent of human-caused extinctions. Estimates range from mild to very severe.

In addition, our evidence for all previous extinction events is geological evidence, and the shortest scales of geological time usually are in the order of several hundred thousand to several million years. Even those extinction events that were caused by instantaneous events -- the Chicxulub asteroid impact being currently the demonstrable example -- unfold through the equivalent of many human lifetimes, due to the complex ecological interactions that are unleashed by the event. So even if the current rate of extinction is higher than the rate during a great mass extinction event, the counter argument runs, as long as the current rate does not last more than a few thousand years, the overall effect will be small. There is still hope, argue some, that humanity can eventually slow the rate of extinction through proper ecological management (see sustainable. Current socio-political trends, argue others, indicate that this idea is overly optimistic (cf Sustainable development and search 'Sustainable' for further topics).