Evolution and extinction

Most scholars agree there have been five major extinction events in the history of the planet. The most recent occurred at the end of the Permian period, about 250 million years ago and resulted in the extinction of 96 percent of marine species and 70 percent of land species. This extinction occurred during a period, like today, when carbon dioxide levels in the atmosphere were rising, the climate was changing and the chemistry of the oceans deteriorated to the extent that then existing life forms could no longer survive.
Elizabeth Kolbert, in her recent book “The Sixth Extinction,” makes the case that we are now in the early stages of the next mass extinction from the planet. Species are continuously evolving and going extinct in our land and water regimes. Evolution and extinction present opposite sides of the coin of life. The coin keeps flipping.

Extinction rates are currently accelerating. We are probably most familiar with mammals because we see them every day. There are about 5,000 known mammalian species alive at present. The “normal” span, from origination to extinction, for a species of mammal might be on the order of a million years. One species might be lost about every 200 years. However, by one count, there are 89 know mammalian extinctions in the last 400 years and another 169 species listed as critically endangered.

What is true for mammals is even more critical for other critters; birds, amphibians, fish, invertebrates, and plants. Some estimates place the current extinction rates for all species at 10,000 times the normal (without humans) level.

Unlike the mass extinction events of geological history, the current extinction scenario is one in which a single species, you and I, appears to be almost wholly responsible. The evolution of the human species has brought with it an expansion in knowledge, capacity to do things, and technology at a far faster rate than at any time in the last four and one-half billion years. In the lifetime of a single generation we have seen development of airplanes and space travel, computers and communication systems that reach and connect the entire world, atomic weapons with the capacity to destroy us all, and medical advances not dreamed of a few decades ago.

Where does this lead us? Species extinction is accelerating and we show little inclination to slow it. We are changing the climate at an unprecedented rate. We have weapons at our disposal capable of creating a planetary wasteland.

We have more knowledge, information, and technology than any time in history. Evolution and extinction grind on. Which side of the coin will face up for the human species?

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