University of South Dakota

Vermillion, SD

“Throughout the fossil record we can see that evolution proceeds in stops and starts. It does not and has not proceeded in a straight line.”

Dr. Jerry Cassidy drew a time line on his white board and put five tics on the graph. He knew that half his students were asleep and the rest only cared because they needed a mid-level science elective to graduate.

“The great extinction events have had a major effect on the biological world. Every so often something happens- asteroid impacts, super-volcanoes- there are numerous causative theories, that force a large number of species to go extinct in a relatively short time. In Earth’s history it has happened five times. Just for laughs, let’s look at the Permian extinction.”

“The Permian Extinction occurred around 250 million years ago. It was so severe that it is often called the Great Dying. Seventy percent of terrestrial species and up to ninety-six percent of marine species went extinct almost overnight. 57% of all families and 83% of all genera became extinct. It’s the only known event that caused mass extinctions among insects. Blastoids, trilobites and eurypterpids, all highly evolved families of organisms, vanished in relatively short order after being plentiful for eons.”

“Mass extinction events have been most harsh on highly specialized organisms because when their environments changed, they couldn’t adapt to new conditions. After mass extinction events only the most robust and adaptable organisms remained. Extinctions have acted like the evolutionary reset switch and afterwards everything changes.”

Cassidy looked at his watch and saw that it was just a few minutes to eleven and said, “All right class. Read chapter 12 and be ready to discuss the five major extinction events and their influence in evolutionary terms. Have a nice weekend.”

Amanda Nelson stopped by his desk and said, “Am I the only one that noticed that you wrote this chapter?”

Cassidy smiled and said, “In this class, Miss Nelson.”

The classroom emptied quickly as Cassidy packed his briefcase for his walk back to his office.

He didn’t notice the men in suits waiting for him just outside the lecture hall.