Question

what is the difference between an explosive adaption and a gradual adaption? also what is a mass extinction in realation to a smaller extiction?

We are dependent on the fossil record to tell us how morphological aspects of life have evolved. But the record is far from complete. The fossil record suggests that the history of life is punctuated by mass extinctions followed by adaptive radiations of the survivors. What we find in the fossil record is the sudden appearance of new forms of species (“sudden” meaning over the course of thousands of years), which persist essentially unchanged for their tenure on Earth, and then disappear from the fossil record just as suddenly as they appeared. Evolutionary biologists have coined the term punctuated equilibrium to describe this non-gradual appearance of species in the fossil record. Punctuated equilibrium refers to an evolutionary pattern in which periods of rapid change are separated by longer periods of little or no change. The explosive adaptation that you are referring to is described as punctuated equilibrium in the fossil record. In contrast to punctuated equilibrium mentioned above, Charles Darwin envisioned a more gradual mode of change. Though both theories could be considered to be separate parts of the whole when considering of the process of evolution. It is the sporadic nature of the fossil record that has lead to such contrasting ideas. As for rates of extinction, a single species may become extinct because its habitat has been destroyed or because the environment has changed in a direction unfavorable to that species; this could be considered a “smaller extinction.” Darwin coined the term natural selection to describe the phenomenon of species’ survival--or extinction based on characteristics that allow them to survive in a changing environment, or cause them to die out. Extinction is in fact inevitable in a changing world, and there have been crises in the history of life when global environmental changes have been so rapid and disruptive that a majority of species were swept away (this is called a mass extinction). There have been five episodes of mass extinction since the Cambrian explosion 540 million years ago. Check out these web sites for more information: Punctuated Equilibrium: http://www.xrefer.com/entry/222489 http://tidepool.st.usm.edu/crswr/gradpuncteq.html Mass Extinctions: http://ic.ucsc.edu/~tlay/eart80a/Lectures/lecture9.html http://www.bbc.co.uk/education/darwin/exfiles/ http://www.igc.apc.org/wri/biodiv/b03-koa.html Madalyn Edwards, NASA Astrobiology Institute
August 22, 2002