As longtime readers of this blog may remember, I’ve quoted from Richard Leakey and Roger Lewin’s 1996 book, The Sixth Extinction; Patterns of Life and the Future of Mankind. Now there’s another book titled The Sixth Extinction (subtitled An Unnatural Order) by Elizabeth Kolbert (sorry, no relation to Steven Colbert…).
Are humans the reason that this wonderful Earth and her inhabitants are all here? Are Homo sapiens the pinnacle of evolution? That and other questions of our evolution are discussed in the chapter “Human Impacts of the Past” in Leakey’s book. Here is a series of excerpts from that original book:
…“For instance, Alfred Russel Wallace, the co-inventor of the theory of natural selection, believed that evolution had been working ‘for untold millions of years…slowly developing forms of life and beauty to culminate in man.’
“Until about a decade ago, most biologists did not feel uncomfortable with speaking of an increase in complexity as an outcome of evolution and using the term progress interchangeably with complexity. Recently, however, a certain nervousness has crept in, so it is now acceptable to talk about complexity, but not about progress. Progress, is it’s argued, implies some kind of mysterious innate tendency for improvement, and that is considered too mystical. …
“Gould was one of the most outspoken in denying progress, asserting that it is ‘a noxious, culturally imbedded, untestable, nonoperational idea that must be replaced if we wish to understand the patterns of history.’
“The ability of the human species to inflict devastation on the natural world at the level of significant extinctions was for a long time thought to be a relatively recent phenomenon in human history. In Wallace’s time, biologists recognized that the swaths of European colonizations of the globe from the seventeenth century onward had left a trail of havoc in nature’s perceived harmony. Many held earlier colonizers, such as the Polynesians throughout the Pacific, to be blameless in this respect, and to have been part of that harmony. (Western sentiments toward technologically primitive societies had in fact swung dramatically, from their being crude and barbaric beasts to being Rousseauean noble savages.) But as Jared Diamond, a biologist at the University of California at Los Angeles, had pointed out, many pre-European societies felt the same about their own forbearers.
“Homo sapiens has become the most dominant species on Earth. Unfortunately, our impact is devastating, and if we continue to destroy the environment as we do today, half the world’s species will become extinct early in the next century.
[Again, this was written at the end of the twentieth century.]
“Even though Homo sapiens is destined for extinction, just like other species in history, we have an ethical imperative to protect nature’s diversity, not destroy it.
“Many people find it impossible to contemplate a time when Home sapiens would no longer exist, so they like to assume that we will break the biological rule and continue forever, or at least until our planet ceases to exist, billions of years from now, when its atmosphere is burned off by an expanding sun.
“The sixth extinction is similar to previous biological catastrophes in many ways. For instance, the most vulnerable species are those whose geographical distribution is limited, those in and near the tropics, and those with large body size. It is unusual in several ways, too, most particularly in that large numbers of plant species are being wiped out, which is unprecedented compared with past crises. But in the end, with passage of five, ten, or twenty million years, despite this and other distortions of the biota that will remain, rebound will occur. ‘On geologic scales, our planet will take care of itself and let time clear the impact of any human malfeasance,’ as Gould has put it. Why, then, if it matters not at all in the long run what we do while we are here, should we concern ourselves with the survival of species that, like us, will eventually be no more?
“We should be concerned because, special though we are in many ways, we are merely an accident of history. We did not arrive on Earth as if from outer space, set down amid a wondrous diversity of life, blessed with a right to do with it what we please. We, like every species with which we share the world, are products of many chance events, leading back to that amazing explosion of life forms half a billion years ago, and beyond that to the origin of life itself. When we understand this intimate connection with the rest of nature in terms of our origins, an ethical imperative follows: it is our duty to protect, not harm them. It is our duty, not because we are the one sentient creature on Earth, which bestows some kind of benevolent superiority on us, but because in a fundamental sense Homo sapiens is on an equal footing with each and every other species here on Earth. And when we understand the Earth’s biota in holistic terms—that is, operating in an interactive whole that produces a healthy and stable living world—we come to see ourselves as part of that whole, not as a privileged species that can exploit with impunity. The recognition that we are rooted in life itself and its well-being demands that we respect other species, not trample them in a blind pursuit of our own ends. And, by the same ethical principle, the fact that one day Homo sapiens will have disappeared from the face of the Earth does not give us license to do whatever we choose while we are here.”
And in Elizabeth Kolbert’s Sixth Extinction, from the prologue:
[Human expansion] “…continues, in fits and starts, for thousands of years, until the species, no longer new, has spread to practically every corner of the globe. At this point, several things happen more or less at once that allow Homo sapiens, as it has come to call itself, to reproduce at an unprecedented rate. In a single century the population doubles; then it doubles again, and then again. Vast forests are razed. Humans do this deliberately, in order to feed themselves. Less deliberately, they shift organisms from one continent to another, reassembling the biosphere.
“Meanwhile, an even stranger and more radical transformation is underway. Having discovered subterranean reserves of energy, humans begin to change the composition of the atmosphere. This in turn, alters the climate and chemistry of the oceans… Some plants and animals adjust by moving. They climb mountains and migrate toward the poles. But a great many—at first hundreds, then thousands, and finally perhaps millions—find themselves marooned. Extinction rates soar, and the texture of life changes.
“No creature has ever altered the life on the planet in this way before, and yet other, comparable events have occurred. Very, very occasionally in the distant past, the planet has undergone change so wrenching that the diversity of life has plummeted. Five of these ancient events were catastrophic enough that they’re put in their own category: the so-called Big Five. In what seems like a fantastic coincidence, but is probably no coincidence at all, the history of these events is recovered just as people come to realize that they are causing another one…”
And speaking of oceans, an article in today’s Washington Post, “What the ‘sixth extinction’ will look like in the oceans: The largest species die off first,” cites a new study of the current mass extinction event and how it is currently affecting marine life.
Atlantic bluefin tuna are corralled by fishing nets during the opening of the season in 2011 for tuna fishing off the coast of Barbate, Cadiz province, southern Spain. (AP Photo/Emilio Morenatti)