Since the beginning of life on Earth there have been five really big ones -- "mega-extinctions -- die offs in which more than half of the species on Earth disappeared. According to many sources, including the very useful and detailed 2005 Millennium Ecosystem Assessment Ecosystems and Human Well-being: Biodiversity Synthesis by the World Resources Institute, species have been disappearing at a rate that is between 100 and 1,000 times the normal rate over the past few hundred years. The rate of die-off has been particularly fast over the past 50 years. It appears that we are in the midst of the sixth mega-extinction. But if you ask people about the current great mass extinction, most will be bewildered; some will think you are crazy.
I surveyed several leading high school environmental science and biology texts for discussions of mass extinctions. Most of them do explain that extinction is part of evolution and that really big extinctions open ecosystem niches that can be occupied by new species. A couple of the books explain that the last great mass extinction, the one that wiped out the dinosaurs 65 million years ago, was followed by the rapid emergence of mammals. (One could make a good argument that humans have the fifth mega-extinction to thank for their current dominant role on the planet.) The environmental science texts discuss the current loss of biodiversity. One of the books that I looked at actually included the idea that we could be in a sixth major mass extinction. In all cases the discussion covered just a few pages in a text that is 600 to over 1,000 pages long.
There are good reasons for this light coverage of the current mass extinction and for the general lack of awareness about it: it is a difficult subject. Kolbert's New Yorker article is a good place to start in thinking about what makes it so difficult.
Extinction and Humans
We know that extinction happens when humans begin to populate an area. This is not just a recent phenomenon. Kolbert traces the relationship between human settlement and extinction back 50,000 years, to the time when the first humans were arriving in Australia.At that time, Australia was home to a fantastic assortment of enormous animals; these included a wombatlike creature the size of a hippo, a land tortoise nearly as big as a VW Beetle, and the giant short-faced kangaroo, which grew to be ten feet tall. Then all of the continent's largest animals disappeared. Every species of marsupial weighing more than two hundred pounds--there were nineteen of them--vanished, as did three species of giant reptiles and a flightless bird with stumpy legs known as Genyornis newtoni.This pattern of sudden die-off coincident with the arrival of the first people in an area was repeated in New Zealand, South America, North America, the Hawaiian Islands and elsewhere. Hunting appears to be the cause in some cases, but cannot explain everything. For example, 90% of Hawaii's bird species disappeared when people first came to the islands. A clue emerges from some work on the Australian extinction.
A few years ago, researchers analyzed hundreds of bits of emu and Genyornis newtoni eggshell, some dating from long before the first people arrived in Australia and some from after. They found that around forty-five thousand years ago, rather abruptly, emus went from eating all sorts of plants to relying mainly on shrubs. The researchers hypothesized that Australia's early settlers periodically set the countryside on fire--perhaps to flush out prey--a practice that would have reduced the variety of plant life. Those animals which, like emus, could cope with the changed landscape survived, while those which, like Genyronis, could not died out.
Unintended Change
Setting fires over large swaths of countryside is clearly a dramatic--and intentional--impact on the ecosystem. So, from an educational standpoint, the story of Genyornis newtoni might be a useful example of how ecosystems work and of the potential impact of large ecosystem changes--an example of the kind of thing that modern day humans shouldn't do.The problem with the much more recent die offs is that the human impacts, though just as devastating, can be subtler and unintentional. Kolbert traveled to Panama to trace the story of the recent sudden die-off of frogs and other amphibians. She portrays the speed with which these massive changes to ecosystems can take place.
In the late nineteen-eighties, a herpetologist named Marty Crump went to Costa Rica to study golden toads; she was forced to change her project because, from one year to the next, the toad essentially vanished. ... Probably simultaneously, in central Costa Rica the populations of twenty species of frogs and toads suddenly crashed. In Ecuador, the jambato toad, a familiar visitor to back-yard gardens, disappeared in a matter of years. And in northeastern Australia biologists noticed that more than a dozen amphibian species, including the southern day frog, one of the more common in the region, were experiencing drastic declines.Kolbert follows the story of these die-offs, going on jungle frog collecting expeditions in the dark of the night and talking with a variety of scientists. Habitat destruction and chemical pollution are undoubtedly important factors, but the principal cause appears to be a chytrid fungus. Chytrid fungi are everywhere. In most cases they play a role in the decomposition and recycling of dead plants and animals. But in this case, a pair of pathologists working on dead frogs from the National Zoo discovered a previously unknown chytrid, Batrachochytrium dendrobatidis (or Bd for short), that breaks down keratin in living amphibians.
Bd is not new; subsequent research found it in frog specimens collected in the 1930s. In particular, it seems common in the African clawed frog, Xenopus laevis. The difference is that the African clawed frog and Bd seem to coexist happily. The problems emerge only when other species of frogs who have never before encountered Bd become infected with the fungus.
The next question, of course, was how did Bd move from South Africa to the Americas? This was an easier question to answer. Again, quoting Kolbert's article:
In the early nineteen-thirties, a British zoologist named Lancelot Hogben discovered that female Xenopus laevis, when injected with certain types of human hormones, laid eggs. His discovery became the basis for a new kind of pregnancy test and, starting in the late nineteen-thirties, thousands of African clawed frogs were exported out of Cape Town. In the nineteen-forties and fifties, it was not uncommon for obstetricians to keep tanks full of the frogs in their offices.Discarding unwanted frogs (African clawed frogs have now been introduced to North and South American and Europe) or even just discarding aquarium water would spread the fungus. It appears that the massive frog die off is an unintended consequence of work by doctors a half century ago.
What is it About Humans?
Kolbert's story is a good example of why extinctions are associated with the presence of humans: by our nature, we change ecosystems.A couple of weeks ago I was previewing the new Ken Burns documentary on National Parks. In the opening few minutes there is footage of grizzly bears standing in a waterfall and catching salmon as the fish leap up over the falls. The bears just catch them in their mouths in mid-leap. Spectacular. No doubt about it: they have eye-mouth coordination that goes way beyond anything I could do. But that does not mean that I can't catch salmon; I would just build a trap.
Humans aren't the biggest, fastest, most physically powerful animals. We survive and and excel as a species by making things and changing things. We set fire to the forest. We turn forests and grasslands into fields in which we cultivate crops. We domesticate animals and move them around into different environments.
There is nothing wrong with this. It's not, at its roots, a moral issue: it's what we do to survive. It's our species' great innovation. But it does have the effect of changing the structure of ecosystems more quickly than the rate at which other species can adapt to change. So they die.
Evolution and Rates of Change
Understanding that life evolves is one of the most basic elements of science literacy. It is a significant learning objective for high school biology classes. One of the key components of that understanding--and a challenge in communicating it to students--has to do with rates of change.One of Darwin's great contributions to our understanding of the world was the notion that great, significant changes in the structure of life could result from the aggregation of many small changes given enough time. His work built directly on the work of Charles Lyell, the founder of modern geology, who made the same observation about changes in the physical structure of the earth. Before Lyell came along, it was generally believed that change came in the form of catastrophic events, such as Noah's flood. Lyell was an advocate for a new paradigm, known as "uniformitarianism," which asserted that the world around us is shaped by slow moving forces that are continual and ongoing.
The idea the enormous changes could result from small effects was a difficult concept in the 19th century, and it is still a difficult thing for students to grasp today. How could water running over rock create the Grand Canyon? How could random mutation and natural selection result in humans? However, I think it is fair to say that most students today do accept these explanations, even if they don't have an intuitive feel for the scales of time and change involved. Over the past century and a half, scientists and educators have successfully established uniformitarianism as the way to understand big changes over time. I suppose we could say that it is another part of science literacy.
Perhaps that is part of why understanding and accepting the notion of mass extinctions is so difficult. They don't happen slowly; they violate the core assumptions of the uniformitarian paradigm. As Kolbert points out, Darwin certainly believed in extinction, but also believed that it only happened slowly. It is only over the last twenty-five years or so that there has been growing acceptance in the scientific community that Darwin was partially wrong: Yes, great changes can happen slowly over long periods of time, but they can also happen quickly.
That notion--that great change can happen quickly as well as slowly--is another candidate idea for inclusion in basic science literacy. That seems particularly true in an era such as the one we are entering. Without that idea, students have no way of getting their hands around the idea that we are in the midst of a sixth great extinction.
Environmental Science Literacy - and Why This One's Difficult
At this point, this is another one of those articles that I need to turn over to the reader. What follows is a quick summary of where we are at.
- Humans are now causing massive extinctions. We know from studies such as the Millennium Ecosystem Assessment that humans have increased the rate of extinction by about 1,000 times over background rates typical of the Earth's history.
- Understanding extinction is fundamental to understanding evolution. Evolution is a basic component of science literacy and a core part of high school science education. The fact that die-offs happen quickly as well as slowly is basic information that people need in order to understand the makeup of the world around them.
- The fact that humans cause extinctions appears to be a fundamental fact of life. Our species' great innovation is the ability to create large scale changes to the environment around us--changes that require language, the ability to plan, and other capabilities that are hallmarks of the species. Large scale, rapid environmental change inevitably kills off some species that depended on the old structure of the ecosystem.
In that article I listed a number of skills and understandings that need to be in place to support comprehension of the concept of rapid mass extinction. Students need some first-hand experience with biodiversity: They need to be able to identify different species themselves, so that they can see the diversity. They need to spend time outdoors so that they have a personal way of valuing richness and diversity. They need practice in working with different time scales and spatial scales. (This kind of practice needs to be the subject of the kinds of "exemplary problems" that support internalization of a scientific paradigm.)
The learning progressions required to support understanding of mass extinction take time and substantial effort. But I think that the biggest barrier to accepting the notion of anthropogenic mass extinction is less conceptual than it is emotional. Thomashow captured the problem with a quotation from a book by Scott Russell Sanders titled Hunting for Hope. The quotation is from Sanders' son:
You make me feel the planet’s dying and people are to blame and nothing can be done about it. There’s no room for hope. Maybe you can get by without hope, but I can’t. I’ve got a lot of living still to do. I have to believe there’s a way we can get out of this mess. Otherwise what’s the point? Why study, why work — why do anything at all if it’s going to hell?How do we respond to such questions? Clearly, there does need to be a focus on hope. But hope for what? That everything will stay the same? That we can avoid mass die-offs? That would be false hope. That the human species can find a way through the current extinction and find a way to live in a changed, but still resilient world? That seems like necessary hope. (See the article "Beyond Naturalness" for more thinking about changed systems and resilience.)
I also wonder whether it might help to move away from some of the moral opprobrium associated with concepts such as mass extinction. It seems that we send the message that extinction is a tragedy and that humans' role in creating biodiversity loss is wrong and should be stopped. That's not possible.
What if, instead, we delivered a message more like, "Yes, humans do cause other species to die off. That's a fact. It happens anytime you introduce big changes in a complex ecosystem. Get over it. What we need to focus on is how to manage and conserve systems so that they are as resilient as they can be. Failure to do that could kill us. Managing ourselves to sustain resilient systems may be the biggest challenge to confront the species. It is an exciting time to be alive." Or something like that -- how would students respond to that message?
Those of you who are teachers -- middle school, high school, or college -- do you introduce students to the concept of mass extinctions? If so, do you make students aware that we are in the midst of another big one? How do you approach that? What problems and insights have you encountered?
Those of you who are students, scientists, resource managers, or simply people concerned about the environment -- what do you think about the idea of making it easier to discuss mass extinction by reducing the emphasis on morality ("Thou shalt not ..."), recognizing that extinction has been and probably will continue to be a consequence of human activity, and focusing on the question of how to manage and minimize extinction? Is this a way to put discussion of extinction and resilience (the countermeasure) back on the table? Or is it starting down a slippery slope?
Let's discuss this.
