TEACHING PUNCTUATED EQUILIBRIUM VS. PHYLETIC GRADUALISM:1972-2012

I taught the main Paleobiology course for junior-level undergraduates each fall at the University of Texas at Austin for 42 years (1971-2012). The course covered a wide variety of topics, including the fossil record, evolution, extinction, classification, plus personal and controversial topics, such as my research as a paleontologist, and new paleontological models that had just been proposed. The students seemed to like controversial topics (were dinosaurs hot-blooded?; did plate tectonics affect fossil ranges?), so I included several of these in the lecture schedule.

In the fall of 1971, I attended the GSA Annual Meeting in Washington, DC, and heard Steve Gould (with coauthor Niles Eldredge) present a talk on Punctuated Equilibrium, a new theory about how speciation occurred in fossils, at a Paleobiology Symposium organized by Tom Schopf. Many of us in the audience thought this was a really interesting and novel idea, but a few other listeners (especially Art Boucot) were not so happy with this new model and argued with Steve.

The actual book chapter by Eldredge and Gould was published in mid 1972, and set off a big argument in paleontology, so I added this topic to my course as a new lecture. I made a detailed outline comparing Phyletic Gradualism with Punctuated Equilibrium for the students to compare before deciding which model they liked the best. I also made 2x2 slides of some of the figures in their chapter, plus charts showing the slow rates at which large populations changed, and how peripheral populations rapidly produced new species and then spread out to occupy new areas. I had a chart showing rates of gradualism (moderate diagonal change), stasis (almost no change near the y-axis), and punctuation (rapid change near the x-axis), and examples of organisms that slowly changed or just oscillated through time. I also pointed out that the book chapter was an unusually strong article that led to hundreds of later papers in Paleobiology, both pro and con, and eventually spread in the early 1980s to additional controversy in Evolutionary Biology. Through the years, I tried to stay relatively neutral in my presentation of this topic, arguing that both types of speciation might occur in different fossil organisms, although my biases favored the Punctuated Equilibrium model.