Tuesday, February 23, 2010

Dead as a Dinosaur

Dinosaurs are frequently cited as the ultimate exemplars of failure. “Dead as a dinosaur” has become deeply embedded in our vernacular. Yet death for a species, and even for groups of species, is as inevitable as your death. Somewhere around 99% of all species that have ever existed are now extinct. The 10-50 million species that comprise the modern day biosphere (the uncertainty due mostly to our lack of understanding of microbial diversity) are but the latest players in a four-billion year drama—“The Greatest Show on Earth,” to borrow the title of Richard Dawkins most recent book.

Similarly, the event that decimated the dinosaurs about 65.5 million years ago killed off only those forms like Tyrannosaurus rex and Triceratops horridus alive at the end of the Cretaceous Period (with the exception of some birds, which managed to survive this biologic bottleneck). Dinosaurs had existed for 160 million years prior to that doomsday event, birthing a bewildering array of forms that succumbed to the scythe of extinction long before a giant asteroid slammed into the Gulf of Mexico. By comparison, we humans have been around a mere 200,000 years or so, and our small clan of bipedal primate cousins originated about 6 million years ago. In other words, dinosaurs are a great success story rather than a bunch of prehistoric washouts.

The notion of dinosaurs as failures underscores a pair of conditions that threaten the persistence of humanity: myopia and hubris. Lacking a meaningful sense of deep time, we tend to lump all pre-human life-forms into a single box labeled “extinct.” Virtually blinded by our severe temporal myopia, we ignore the multi-billion-year skein of lifeforms, the dramatic comings and goings of organisms through the geologic ages. Meanwhile, our hubris derives from a worldview that transforms other life forms to objects, and places humans not only outside but superior to (nonhuman) nature. While I confess to a certain personal bias on the matter, it’s simply ridiculous to thumb our noses at dinosaurs and laugh derisively at their present day absence. We might as well speak contemptuously of our great grandparents; after all, they’re no longer with us.

Ecology and evolution are deeply intertwined. Just as the death and decay of organisms provide raw materials for subsequent generations, so too the deaths of species spawn new possibilities for future generations of species. Without extinction, there would be insufficient ecological space for evolution to explore alternative solutions and diversify into new life forms. When initially faced with some change to their native environments, species don’t grimly stay put and evolve into new forms better suited to the transformed conditions. They move, tracking the old habitat. In general, it’s only when the old habitat disappears that species are forced to adapt or die. Mass extinctions—the dying off of multiple, distantly-related lineages over vast areas in a short span of time—occur when external forces alter or wipe out a range of environmental settings, cutting off opportunities for tracking habitats.

Over the past half billion (500 million) years, there have been five major mass extinctions, with the dinosaurs wiped out in the most recent of these. We now face the sixth mass extinction, which threatens to tear apart the fabric of the biosphere and wreak drastic consequences for most life on this planet, including us. In better times, species losses tick along at a barely discernable rate—perhaps one every five years. At present, somewhere between 50 and 150 species disappear every day, never to be seen again. (Once again, uncertainty in the actual value comes mostly from a lack of basic knowledge about how many species exist.)

This time around, a single species—Homo sapiens—has become the external force driving the decimation of millions of other species. Yes, we are the asteroid now colliding with the planet. The list of anthropogenic factors is all too familiar, among them habitat destruction, overhunting, toxic pollution, and climate change. In particular, the duo of global warming and environmental destruction has eradicated habitats at a pace far exceeding the abilities of many species to track or evolve. At the current rate of extinction, about half of all species alive today will be extinguished by the close of the 21st Century, an eco-evolutionary experiment not run since the end of the Cretaceous. Paleontology teaches us that the biosphere takes up to 10 million years to recover from a major mass extinction. So the decisions we make today will have cascading consequences well into the unimaginable future.

Are we (currently) capable of wiping out life on Earth? No. Although this claim is commonly made, life has persisted without hiatus for almost four billion years, and it will be here long after the last human. Life forms at the small to microscopic end of the size spectrum are the most resilient, some of them hunkered down miles below the Earth’s surface. Humanity, on the other hand, is nowhere near immune from the profound changes now taking place. Like it or not, we are inextricably embedded into nonhuman nature and dependent on its flows of energy, food, and water for our very survival, as well as for our physical, mental, and emotional health. So we have every reason to raise our awareness of these issues and act accordingly.

Nevertheless, notwithstanding many years of dire warnings from biologists, the sixth extinction has barely touched the collective consciousness of Western cultures. Global warming currently garners the media spotlight, yet recent polls show a significant drop in the numbers of people concerned about this issue. Despite the bounty of rhetoric, we’re not behaving as if we live on a planet in peril. Consider the recent climate change summit in Copenhagen, where world leaders had a unique opportunity to make history, but failed to reach a meaningful agreement. At this pivotal moment in history, we lack the strength of public opinion necessary to spearhead a WW II-style mobilization to achieve sustainability. Why?

In large part because we’re crippled by an outdated worldview. As a species, we need new glasses capable of curing our temporal myopia and inserting us back into the evolutionary epic--the Great Story. We need a mindset that moves beyond our human-centered hubris and inserts us back into the natural world. Learning the scientific truth of the matter is part of the solution, but connecting with the nonhuman world through direct experience is equally important. Those of us raised in urban settings may find it tough to establish meaningful connections of this sort, but we can make key steps in the right direction. We can also encourage our children move beyond our limited perspective—to see the world in new, healthier ways that are truer to our nature and critical for a sustainable future.

"But hold on a minute Sampson," I can hear you saying. "If all species eventually go extinct anyway, why should I lose sleep over the current hemorrhaging of life forms?" The answer to this question comes down to ethics, morals, and values. Do we have the right to kill off other species? Do we have the right to rob future human generations of the opportunity to see a whale, a tiger, or an elephant in the wild? More to the point for most of us, is it reasonable that we knowingly bring about the downfall of civilization while alternative paths lie before us, untaken? Your call.

(Image credit: Tyrannosaurus and Triceratops, by Michael Skrepnick)


  1. Good article. I may use it for my high school biology class!

    A quick question, I have seen this quote over and over but can never find out its actual source
    "Somewhere around 99.9% of all species that have existed are now extinct"
    The best I could track the quote down was to Stephen J. Gould who used it in one of his popular science books (don't remember which one right now) with no reference to a legitimate journal article.
    Any ideas where this number was established?

  2. Kyle,

    I am not aware of any rigorous study that this number is based upon, though I have seen it in various publications (including, I believe, E. O. Wilson's book "The Creation"). Nevertheless, it is safe to say that this estimate is at best an educated guess, given our ignorance of the present diversity of life on Earth, let alone diversities during past geologic time periods. Having said that, with the rampant turnover of species through billions of years of deep time, it seems reasonable to conclude that the extant representatives are but a fraction of 1% of the total number of varieties that have existed on this planet.

    Best, Scott

  3. Thanks Scott,
    I see how that makes sense, I just wondered if someone had actually published it and if so how did they calculate past species diversity (especially given that the best we can estimate is anywhere from 5 million to 100 million species currently alive today).

    I am just ending teaching my unit on ecology and moving into evolution and we are starting with an exercise about dinosaurs (based on the PBS evolution web site) and this article will make a great transition.

    Thanks again

  4. Kyle: Interesting post. I'm curious about the source of your statement, "At present, somewhere between 50 and 150 species disappear every day,..." Thanks, don

  5. Have to say Scott, I always find these posts very inspiring. I'm currently finishing off the last semester (before transferring elsewhere) of a two year community college, and it's based in an incredibly conservative area of Wyoming. When the majority of people one runs into think that global warming is nothing but a conspiracy run by rich people 'somewhere else', it's harder to remember that there are people who actively speak out about these issues and are well aware of their importance.


  6. Regarding the statistics about species losses, the numbers have a considerabel range but are invariably high, and frightening. One key reference is:

    Norman Myers and Andrew H. Knoll "How Will the Sixth Extinction Affect the Evolution of Species?" American Institute of Biological Sciences, May 2001.

    A website devoted to the Sixth Extinction can be found at:


    In particular I recommend a 1993 article listed there by E. O. Wilson, "Is Humanity Suicidal," in which he summarizes the process of how we calculate species losses. Unfortunately, things have become even more dire since Wilson wrote this powerful piece.


  7. With regards to the "99.9% of all species are extinct" statement, I have been trying to track down the actual citation for several months now. The closest I have come is:

    Raup, D.M. 1981. Extinction: bad genes or bad luck? Acta Geologica Hispanica 16(1-2):25-33.

    In this paper, Raup states (on pg 25) "Virtually all species that have ever lived are now extinct." Later, he goes on to say "With nearly 600 hundred million years of high diversity in the Phanerozoic record, it is clear that species turnover is relatively rapid. Because the number of living species is large, the net rate of species formation must have exceeded the net extinction rate but when speciation and extinction rates are expressed on a per lineage per million years basis, the two rates are, to a first approximation, the same."

    I presume that this is where the 99.9% extinction rate throughout time comes from. If anyone can suggest a better citation, I'd love to see it.

    BTW, Scott - Darren and I are looking forward to seeing you at the APS conference in a couple of weeks. I'll be in line awaiting an autograph in "Dinosaur Odyssey". : )

  8. It occurs to me that I may have left an identical comment on an earlier post... apologies for repeating myself if so. ;-)

  9. Thank you.

    We need more science communicators. I hope the next generation of communicators, a cohort of which I consider you a member, fill the empty shoes left behind by Sagan and Gould. It particularly saddens me to think of the aging of Richard. I hope you consider publishing children's literature in the near future (I just purchased your one book).

    The world needs a little help.

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