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IN THIS SECTION: Species-scape | Sixth Extinction | HIPPO

Biologists have identified five different and distinct periods when the Earth went through drastic and sometimes cataclysmic environmental changes that destroyed significant percentages of animal life on the planet. It generally takes over five million years for evolution to restore most of the diversity in the animal kingdom, and a complete recovery can take tens of millions of years!

photo of tigerNow, biologists say that we are currently in the midst of the 6th Extinction. While Nature still plays a role in this process, human activities have accelerated the destruction of species in this 6th Extinction.

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The Tree of Life illustrates the difference between the evolution of a new specie and the growing rate of extinction.


The goal is not to preserve the existence of any one species. All species have a natural rate of extinction as evolution refines and redefines organisms according to environmental and genetic changes. During the first five periods of extinction, the rate of extinction was in balance with the rate of the creation of new species.

However, in the period of the 6th extinction, species are disappearing at a faster than normal rate. Pollution, the introduction of "exotic" species and destruction of habitat all contribute to this accelerated pace of extinction.

Thousands of species of plants and animals are still unidentified by scientists. But many will go extinct before we can understand the role they play in their ecosystems. And we could be destroying plants and animals that may hold the key to undiscovered medicines and chemical products beneficial to humans.

Many pharmaceuticals use substances produced by plants - such as aspirin, which is derived from the meadowsweet plant. Most patients of two of the deadliest cancers - Hodgkins' disease and acute lymphocytic leukemia - can now take drugs derived from rosy periwinkle, a plant found in Madagascar, to treat their deadly illnesses.

Lots of insects communicate and defend themselves chemically - and humans may be able to use these chemicals to treat diseases and make other helpful chemicals. For instance, an anti-coagulant derived from the saliva of leeches is used to treat rheumatism, hemorrhoids and other conditions. And if leech spit proves beneficial, who know what other miraculous cures the animal world will yield.

nextLearn about the factors that
contribute to the
destruction of biodiversity.


An estimated 27,000 species go extinct in the rainforests alone every year. This translates to an average of 74 species disappearing every day -- that's three species disappearing forever every hour!



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updated September 11, 2000

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