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roundtable:a modern mass extinction Watch Show 3:
"Extinction!" on PBS
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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: 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?
Panelist Responses: < back to intro page
Daniel Simberloff
It provides quite a bit of a context. With respect to Ariel's contention, for example -- that we're shortchanging species' abilities to adapt evolutionary to changing circumstances -- we have quite a good understanding of how quickly species can adapt to changed circumstances, and I think that that knowledge suggests that they're not very good at it. Not at doing it very rapidly, anyway.

Also, I'm not completely sure what the listener meant by evolutionary thought, but certainly a lot of what we call evolutionary thought entails knowledge of the geological past and evolution in the past, and that context is very important. It makes it possible to ask what might be the consequences of a loss of 10 percent of species, 20 percent of species, because we have some knowledge of that, from having studied the geological past. The past extinctions, particularly the mass extinctions, greatly affected the subsequent course of evolution, because the survivors were not a random representative small set of the existing biota at the time of the extinction, but they had certain features, and those determine the starting point of the next group of species.
Peter Ward
Quite often people look at the past mass extinctions and they see that subsequent to them there's a recovery of fauna, and then quite often a new suite of organisms. And quite often I'm given this sense that people say, Well, look, mass extinctions therefore aren't really bad things at all. They're good things, because if we had not had the disappearance of the dinosaurs we would not have had [the diversity of] mammals, therefore no humans. Therefore, how can you say that a mass extinction is a bad thing? And, as devil's advocate, you can pose the question, perhaps that this current mass extinction we're in will lead to an even more interesting biota.

And I would respond to that -- and this, again, is coming from Norman Myers, who has published a number of very interesting articles about the future of evolution -- with the fact that most mass extinctions occur when some [cause of] environmental degradation puts a finger on an extinction trigger and kind of fires away, and then, sooner or later, that finger on the trigger goes away, and the conditions that led to extinction stop, and you get this recovery fauna.

But, since humans are the finger on the trigger, because we are the causative agent of the mass extinction, through habitat destruction and habitat perturbation, until humans go extinct the conditions that are creating this extinction will continue. And it is my own point of view that humans, essentially, may never go extinct. I see us as so adaptable, so able to change our circumstances, that I think we are the least endangered species on the planet.

And this is where I'm not at all sanguine about some wonderful new age occurring after this. I think we have made conditions such that we cannot produce, through speciation, new mega-mammals. It's clear that you need gigantic areas for mammal species, [you need] to have lots of open habitat to allow speciation processes to take place, and that will never happen on this planet until roads and fences go away.

So I suspect we are going into a period of very reduced biodiversity, and that as long as we're around, it will be around.
Ariel Lugo
There's three things I would like to say. First, if we relied only on what we observe, we would not be expecting much to happen, because observations cover such a small fraction of the Earth's biota and the Earth phenomena. So that's why you need to rely on theory such as the evolutionary theory, that gives you a framework to explain things and anticipate the long-term dynamics of populations and species.

But, on the subject of humans, I think where we need to be careful is that we don't ascribe value to us being around, whether it's good or bad. I think that's a mistake. Humans are creating change, and we're creating new conditions that probably are going to select for a new mix of species. Now, I don't know what that mix is going to be, but I don't think that just because we prevail for a long period of time we are going to take everybody to extinction. We're just selecting for new kinds of species, new life history characteristics, new combinations, new types of ecosystems. And there's a question coming up about the size of organisms. I think it's pretty obvious that the certain types of organisms don't match well with a human organism, but that there are others that do.

And so what the ultimate balance is going to be, again, I have no idea, but I think that I can see the humans as just another force of change. And if evolution tells us something, it's that the biota readjusts. There has been constant change in the kinds and the diversity of species, over time, in response to environmental change. But interestingly enough, the functions of the biota, they haven't changed. You still have your production, and you have your nutrient cycling, and you have your respiration, and so forth.

So the functions continue, but the actors change. And the challenge is for us to begin to look more closely at what are the environments that humans are creating, and what are the characteristics of those environments, and what is the biology of those environments. And we might be surprised, I think.
Peter Ward
I've just finished [writing] a book called Future Evolution, and we thought, my colleagues and I, for a couple of years about what the next evolutionary fauna might look like, based on human habitats. And our conclusion is that we're really looking at an age of the rat, since we have agricultural fields, where rodents do really well, and cities, where rodents do really well, and that our bet is that, in terms of increased biodiversity, it's going to be among the rodents and the insects.
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