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Talk About Teaching And Learning

Teaching and Learning—About Evolution

Paul Sniegowski

Evolution is the unifying theory of biology. With its main themes of common descent and natural selection, evolutionary biology provides our scientifically accepted explanation for the diversity and adaptedness of living things. At a time when over 40% of adults polled in our country reject the evolutionary basis of modern biology, teaching and learning about evolution is both a serious challenge and an opportunity; one hopes that it will make a difference to turn out college graduates who can play an informed role in public dialogue about evolution and about science in general.

It is too easy to conclude that all of the difficulties that people have with accepting evolution are religious. Interactions with Penn students in our introductory and higher-level biology courses have suggested to me that there are some conceptual blocks to understanding evolution that have little direct connection with religious faith and instead are perhaps a consequence of our innate mental makeup or products of early education. It seems to help if discussions of evolution in the classroom start with four general topics: 1) our restricted perception of time; 2) our tendency to think in abstract “types” rather than to perceive variability and diversity; 3) the fundamental utility of assuming that the laws and processes we can observe in action in the present have operated in the past and will operate in the future; and 4) our difficulty in perceiving gradual change.

Most of us, in our lifetimes, interact with no more than a few generations of human beings. If we are lucky, we might remember our great-grandparents and see our great-grandchildren. Our natural conception of time is surely conditioned by this limited horizon. Historians, of course, learn to see farther into the past than the rest of us, but the “deep time” of Earth history is almost inconceivably longer than human history and leaves scope for vast accumulations of cause and effect. To take an example: Geologists tell us that the mountains north and west of Philadelphia have risen to towering heights and eroded away three times in the past 500 million years. This 500 million year period, in turn, is less than 1/7th of the total time that life is thought to have existed on Earth. Clearly, we can’t feel our way intuitively to a perception of the immensity of time over which biological processes have played out. It has to be thought through with some effort.

Anyone who has spent time observing very young children will marvel at the way in which, once they reach a certain age, human beings become extraordinarily adept at idealizing and categorizing things. It seems that our minds are naturally very good at reducing the variety of forms in our environment to abstract, Platonic types. (We are also, unfortunately, good at stereotyping people.) This “typing” tendency carries over into our natural attitude toward living creatures. One of Charles Darwin’s great scholarly achievements was to emphasize and document in voluminous detail the fact that populations of organisms are quite variable. Again—as with the perception of time—grasping this variability requires some effort. I enjoy telling students after our first lecture on evolution to go out and look at the pigeons on campus with a different attitude. They (pigeons and students) are, of course, amazingly variable, as are most living populations. The easily ignored variability of natural populations, which is continually added to and modified by new mutations, is the stuff that natural selection sorts through over vast stretches of time.

When you park your car at the end of the day, it is reasonable for you to expect that it will start  for you when you turn the key the next morning. That is, you implicitly assume that the same natural processes that caused your car to work yesterday will operate today. (Although I suppose many of us have had cars that seem to violate this assumption at one time or another!) Historical sciences such as evolutionary biology, geology, archaeology, and astronomy operate with this assumption that natural causes have worked in the same way throughout time; detectives and forensics experts operate under the same assumption. Processes that we can observe directly today—changes in population averages, minor geological erosion events, the births of new stars in nebulae—were in all likelihood operating in the past and will operate in the future. In other words, the present is not just the present: it offers windows into the past and to some extent the future, if we know how to look through them. Again, this capacity does not necessarily come naturally: Detectives and forensics experts need a lot of training in methods of recovering the past, as do scientists in the more historical disciplines.

We are not very good at perceiving accumulated change, even in our own lifetimes. How many of us in middle age and beyond have asked “Did I really dress like that 20 years ago?” on seeing an old family photo? Where the natural world is concerned, I would hazard a guess that we have a tendency to assume that things are in rough stasis most of the time and major changes are not on the way. Understanding evolution requires that we be educated away from this falsely reassuring perspective and instead learn to perceive and even anticipate change in the natural world. There is real, practical value to such a shift in perspective. To take an obvious example: the evolution of widespread antibiotic resistance in bacterial pathogens in the late 20th century could have been anticipated and perhaps even retarded if evolution had been part of the standard training for physicians during this time. As it is, you are probably more at risk of dying from a drug-resistant bacterial infection now than you would have been 30 years ago.

There is, of course, a long history of religious opposition to evolution in the United States. Its most recent manifestation is “intelligent design”, the re-airing of the pre-Darwinian notion that the complexity of living things requires a designer and cannot emerge from natural causes. The publicity campaign associated with intelligent design asserts that scientists have a responsibility to “teach the controversy” about evolution. In reality, there is no scientific controversy over evolution; there is only public controversy. The supposed points of scientific controversy related to intelligent design were settled in the 19th century, and any good course in evolution spends time covering this in its introduction to the historical evidence for evolution.

Evolutionary biology is a science; it is not a belief system. In my experience, students are often visibly relieved to hear the opinion that acceptance of the conclusions of evolutionary science, while it may challenge some of their beliefs, does not obligate them to be unbelievers. In our 200-level evolution course, we devote a week’s recitation session to readings about evolution and creationism, and we open the discussion to matters of science and faith. It has been inspiring to see the courtesy with which students of diverse beliefs and unbeliefs treat one another in these lively discussions. Such discussions suggest a possible way out of the current public controversies over evolution and religion. Perhaps our innate tendency to stereotype one another can be overcome after all.

Paul Sniegowski, associate professor of biology, is the 2005 recipient of SAS’s Ira H. Abrams Memorial Award for Distinguished Teaching.

This essay continues the series that began in the fall of 1994 as the joint creation of the College of Arts and Sciences and the Lindback Society for Distinguished Teaching.

See www.upenn.edu/almanac/teach/teachall.html for the previous essays.



  Almanac, Vol. 52, No. 14, December 6, 2005


December 6, 2005
Volume 52 Number 14


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