What Was I Thinking? Remembrances of My Dissertation

In 1987, I submitted my Ph.D. thesis, “Environmental Variability and Phenotypic Flexibility in Plants,” at the University of Illinois. What was I thinking? I was dealing with three variables: plants, the growth flexibility of those plants, and the variability of the environment—in this case, of sunlight intensity. I intended to write about all three of these things in this essay, but it quickly got out of hand, so I will just tell you about how I dealt with the complex problem of measuring environmental variability in three habitats: abandoned agricultural fields, tallgrass prairies, and forest floors.

One of the major problems with measuring environmental variability is construct validity—that is, how valid is a way of measuring something so that it is a believable construct of what you claim to be measuring? I explain this concept in my book Scientifically Thinking. There is no single valid way of measuring environmental variability. What I did instead was to measure it three different ways. If these three ways all gave the same results, then they were probably valid, and I could believe the results.

First, I made instantaneous measurements of light (that is, the colors of light that stimulate photosynthesis) with a “quantum sensor” designed to do exactly this thing. The problem is, this kind of light intensity varies from one moment to the next.

So I used a second method. What I really wanted to know was the spatial patchiness of shade caused by leaves. So I made three-dimensional profiles of leaf area in the three habitat types. To do this, I used nine pieces of wood, a string, and a nail. But neither of these methods could prove that variability of sunlight intensity would actually have an effect on plants.

So I used a third method as well. I used phytometers, that is, actual potted plants. I measured the weight of the plants (plus the soil, or course) in lots of different places in the three habitats in the morning and the afternoon. I measured environmental variability as the differences in how much water the plants transpired.

This was how I tackled the problem of construct validity. I measured what I wanted to know three different ways. I was taking a chance. What if the three ways gave three different answers? But I got lucky. All three methods agreed. Chalk one up for construct validity.

I had expected that weedy fields would be the most variable, the forest floor the least variable, and prairies intermediate between them. And this is what I found. I still marvel that it came out that way.

I announced my results triumphantly: weeds had the most phenotypic flexibility and lived in the most variable environment; forest floor plants had the least flexibility, and lived in the least variable environment; and prairie plants and their environment were intermediate. The results all lined up. Despite all of its limitations, this quixotic quest was successful. I believe the results, largely because I took a risk with construct validity, and it paid off. There is no way I could have gotten these results by sheer luck. Here is the plain English summary of my thesis.

A lot of the scientific method is about validity. You have to measure it, and every time you do, you are taking a risk. But if it works, you are closer to understanding the world.

An Unusually Creative Place

In 1987 I had the privilege of earning my Ph.D. at the University of Illinois in what was at that time called the School of Life Sciences. Having nothing else to which to compare it at the time, I did not realize what a privilege it was.

At that time, the biology faculty at the U of I included some truly creative thinkers, who were not merely competent at advancing knowledge in their fields but also investigated the connections among different fields of intellectual inquiry. That is, these remarkable individuals contributed greatly to what E. O. Wilson calls consilience. I would just like to mention a few of them here.

One of them was my advisor, the late Fakhri A. Bazzaz. He saw plant ecology as a complex and global set of processes that included human effects on the natural world. He was interested in anything and everything that affected plants and anything and everything that plants did in the world. He brought together graduate students and professional collaborators who were interested in ecophysiology, population genetics, conservation, plant reproduction, coevolution, and global climate change. He was not the world leader in any of these fields, but was incomparable in bringing them together. He was always enthusiastic. His booming happy voice was a mainstay of our lab.

Another unusually creative person at Illinois was the late Carl Woese (see my earlier essay about him). He was good at doing the (at the time) tedious work of determining base sequences of microbial genes. But his goal was to understand the evolution of all of life. This is what led him to recognize the Archaea as a separate line of evolution. But he also speculated about the origin of life and how evolution fit in with the basic physical processes of the universe. I took a seminar from him in which we discussed some basic ideas about evolution, including some possible overlaps with eastern religion and philosophy.

Another such person was Mary Willson, who now lives in Alaska. She first showed her creativity by moving her research interest from birds to plants (which she called “sessile green birds”). She was looking for ideas that united evolutionary lineages as unrelated as plants and birds. One of those was sexual selection. She, along with Nancy Burley, was one of the pioneers in the study of sexual selection in plants. Most of us simply learned about double fertilization in flowering plants, in which one sperm nucleus fertilized an egg nucleus, producing an embryo, while the other sperm nucleus fertilized the two polar nuclei, producing a triploid endosperm. That’s just the way it is. Willson wondered why. If the endosperm is simply a source of food, to be eaten by the embryo, why should it be the product of fertilization? And, moreover, why should it be triploid? Did the double dose of genes from the female parent allow it some extra measure of control over the embryo inside the seed? A recent article in the Proceedings of the National Academy of Sciences provided some evidence that a close genetic relationship between embryo and endosperm facilitated altruism. This astonishing idea had its roots in what Mary Willson had written three decades earlier.

A fourth example is May Berenbaum, who is still a remarkably productive member of the U of I faculty and the National Academy of Sciences. Her enthusiasm for understanding the coevolution of plants and the insects that ate them spilled over into a zeal for opening the eyes of the public to an understanding of insects. She has written numerous popular books about insects, and about 1981 started what has become an annual tradition at the U of I: the Insect Fear Film Festival.

Of course, every faculty member I knew at Illinois in the 1980s was remarkably competent in their fields, a tradition that continues today. But these four individuals stood or stand out for their creativity. As a result, I was inspired to think creatively about the big picture, and to ask big questions, rather than to focus exclusively on a narrow range of research. What a remarkable privilege this experience was.