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Theoretical Issues in Plant Biology

Panel Discussion

Q:  Is it possible that we are now experiencing a natural global cycle of extinction?

A:  To answer this question, look at the larger context of the last two million years, which are the glacial ages. We are simply in an inter-glacial period and a sequence of perhaps as many as 28 or 30 cycles in which the earth went back to full glacial/inter-glacial. During that whole sequence of cycles, of the last roughly 2.5 million years, there have not been major patterns of extinction. There has been extinction. We can watch interesting things like beavers the size of this table, and mastodons and other things that would be really interesting to see in zoos, but it's not a mass extinction per se. So as the context of the global variation of climate and environment is occurring, the present extinction speeds up. It is occurring in circumstances that are the same as in these roughly 28-30 previous cycles, in roughly the last 2.5 million years.

So, from a paleontological perspective, I would say no, it is not a natural phenomenon. It is a man made phenomenon, although it's clearly a somatic problem because we are indeed a product of natural selection and evolution, so presumably we are a natural element on this planet. And that's why I came back to my particular statement as what makes us stand out. As far as we know, we are the first element on the planet that is conscious of the history and of what we do.

Q:   Isn't extinction a natural process? Won't surviving species diversify to fill the voids?

A:  One way or another, we are eliminating a variety of species at a pace such that species cannot essentially cope with the pressures exerted on them. The pressures we are bringing to bear on these natural communities are part of the natural biology that produces unnatural effects. Take that one step further. In a sense, I can look back at a loss of variation occurring in the past, and the biotic exchange that has occurred, and I can see from today's presentation that introductions from different continents, exchanges, as simply being something that has occurred in the past, and are not abnormal. What is abnormal, just to underscore Karl's point, is the pace at which it is occurring. In the past, plate tectonic movements measure just millimeters per year. Continental collisions occurred over hundreds of thousands and millions of years and indeed, the biotic organisms had a chance to, over many, many generations accommodate each other, as they met each other and grew as a result of their coming together. Were doing all that in a score of these and were just swamping the potential for genetic variation in successive generations, to cope with it.


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