Designing Nature Reserves: past, present and future.
Craighead: Thanks, Tom. This is a great honor for me to be here, especially to talk to a bunch of high school teachers because you and your students are really the key to changing the way we think and live with other species.
The first time I came to Golden Gate Park was the summer of 1968. It was quite a different experience then. My brother and I drove down here from Wyoming and we were kind of nerds in a sea of flower children. But it was really interesting. I felt kind of like a tourist.
Periods of mass extinctions:
I'll pick up where Dr. Roopnarine left off mentioning about the fossil record and that much of what we know about speciation and evolution and past extinctions has been learned from marine invertebrates and I think mainly bivalves. As he mentioned, there were episodes of mass extinctions in the past. Most paleontologists speak of five major episodes that occurred millions of years ago. These were periods of relatively short time (on the order of a few million years), when a large proportion of species in various diverse taxa, and over wide areas of the globe, all went extinct.
Another period of mass extinction, which was not as large or widespread, occurred just about 15-25,000 years ago at the end of the Pleistocene when about 80 percent of the large mammal fauna in North and South America and Australia all went extinct. Some scientists speculate that humans had played a part in this extinction. Today, most biologists will agree that we are in the midst of another period of extinctions. We don't really know how extensive it will be relative to previous events, but it is qualitatively different because it's primarily being caused by human beings.
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