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roundtable:a modern mass extinction Watch Show 3:
"Extinction!" on PBS
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select a question from below
First, a general question. Are we now in a mass extinction, and if so, why does it matter?
Some Web visitors wrote to say they have heard it said, especially of tropical and marine organisms, that we are losing species before we even know of them. And the question is, if we haven't discovered a species yet, how do we know that we've lost it?
Would Darwin support the Federal Endangered Species Act? Millions of dollars are spent by corporations and government for habitat conservation plans, recovery plans, etc., for species that seem doomed for extinction. Is this a wise use of money? Why or why not?
If extinction and mass extinctions are a natural part of Earth's history, should we really be concerned about our effects on endangered species? Are we trying to fight something that's inevitable anyway and that is much larger than us, as a single species ourselves?
I'm concerned with the loss of genetic diversity because it affects food supply, drug discoveries, and the stability of ecosystems on which we depend. And yet, I'm very skeptical of the theory of evolution as it now stands. How does the theory of evolution -- or we could also say that as evolutionary thought -- explain and predict what's going on with the current cycle of extinction, better than if we had to just rely on what we can observe? In other words, what context and what value does evolutionary thought provide to this discussion that we're having?
Several other questions relate to this: Loss of biodiversity, water and air pollution, and the greenhouse effect are all impacting the biosphere, and if these are indeed combining to produce a mass extinction, do you think our species will survive it? Peter's already said that he thinks yes. How about some other perspectives?
Let's move onto some more specific questions. Why do bigger species go extinct faster than smaller ones?
Do you feel that extinctions of large Ice Age mammals had any human causes?
Another Web user wrote: I know there is a gene databank under construction right now. Could this be used as a modern Noah's Ark for the future?
We'll wrap up with a different kind of question. There was one that came from a younger visitor to the Web site who asked, What can kids do to help save the rain forest and animals?


Q: First, a general question. Are we now in a mass extinction, and if so, why does it matter?
Panelist Responses: < back to intro page
Tundi Agardi
I think it's too early to say whether we're actually in a mass extinction. I think it's very alarming to look at the trends that are appearing before us at this current time, and, of course, only hindsight will be able to tell us whether this is going to be a mass extinction of the proportion that we've seen in geologic time.

However, I think that many, many scientists are worried about not just the alarming rate of species loss, but also, perhaps more importantly, the alarming rate of loss of habitats around the world, the higher level of diversity. So I would say it's probably too early to tell whether this is going to be a mass extinction of geologic time proportion, but I think it's certainly an alarming situation that we're in right now.
Daniel Simberloff
I'm actually certain that we're in the midst of a mass extinction. Geologically, there have been five periods in which upwards of 20 percent of the Earth's species, in one case maybe 90 percent of the Earth's species, went extinct, and there've been about 20 or so others in which anywhere from two to 10 percent of species have gone extinct. And certainly over the last few hundred years there are enough extinctions to qualify us in the second category. There's documentary evidence, in some cases, for this.

And it's an ongoing process. It's not slowing down -- if anything, it appears to be accelerating. So I think it's quite possible that we'll eventually be in a situation that qualifies as one of the great mass extinctions.
Peter Ward
I'd like to echo what Dan has said. I agree entirely. Geologists, I think, see this in terms of time scales that most of us probably don't think of. We think of the next 100 years or the next 300 years as the overall time scale over which much biotic impoverishment may take place. But I've spent my life looking at the past mass extinctions. Certainly the fastest we have on record was the end of the dinosaurs, the so-called K/T extinction, but over the last five years we've looked in great detail at what happened at the end of the Permian and what happened at the end of the Triassic, and neither of these were events that took place in, let's say, a 100-year time scale or a 300-year time scale. I think in the past, if we use the past as a record, 100,000 year intervals of mass extinction are certainly what has taken place.

My view of the current mass extinction is that it has been going on for 15,000 years. The loss of the mega-mammals, to me, was really the opening shot of what's going on, and it is now filtering down to ever-smaller animals. But in North America alone we can lose over 50 species in large mammals. This is far more catastrophic than happened in North America with the loss of all the dinosaurs. More large mammals disappeared in 15,000 years than there were species of dinosaurs recorded from the upper most deposits in North America.
Ariel Lugo
I agree with what Tundi said, and I would just add that I think the major concern is the loss of habitat. But I would also say that in addition to losing habitats, we're also creating new habitats, and so what I think has happened is an incredible rearrangement of the relationship among species by this human factor. Some people say we're homogenizing the planet. I'm not sure we are, but we're certainly stirring up the planet and we are creating conditions by which you get species groupings that are new to the biosphere. And where this will take us, I have no idea.

But I would think that a mass extinction like the one shown in the program, I don't think that that's happening. But Peter Ward puts it in a longer time span, and I think when you take that broad look at it, and look at the effect of humans since the time we started, then I think that we might be on a path that will lead us to a lot of extinctions. But I don't think we have an idea where it's going to take us.
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