Carl Sagan once observed that “Extinction is the rule. Survival is the exception”. Indeed, it is estimated that 99.9% of all plant and animal species that have ever existed are now extinct. It is just a matter of time before the same is true of those species that exist today. Thus, whereas Benjamin Franklin said that “in this world, nothing can be certain, except death and taxes”, he might have added to that list of certainties the “death of taxa”.
While extinction of a species is inevitable, its timing is not. There is thus good reason not to be apathetic about recent reports that humanity has wiped out 60% of (non-human) vertebrate populations since 1970. The phenomenon of anthropogenic extinctions is as old as our species. This is not to deny that there were mass extinctions as result of other causes, long before there were humans. However, humans have been driving extinctions since our emergence, including the extinction of 83% of all mammal species. For example, the number of megafauna species in Africa dropped as humans emerged. The rate of large mammal extinctions was significantly greater as humans migrated to the other continents (and to Madagascar).
Although large animals, such as the woolly mammoth, were at greatest risk of human-induced extinction as a result of their size, vertebrate species of all sizes, terrestrial and aquatic, have been affected, including the dodo, the quagga, the Tecopa pupfish, and the once multitudinous passenger pigeon. One result is that today, of all the mammals on earth, 36% are humans, 60% are our livestock, and only 4% are wild animals. 70% of all birds are chickens or other poultry, and only 30% are wild.
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