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.

What Do You Do with an Old Thesis?

I defended my Ph.D. thesis in Plant Biology at the University of Illinois in 1986 and graduated in 1987. This was back in the microfilm days. Can anyone find my thesis online? I can’t. I still have a paper copy (made back in the days of hand-drawn figures).

One thing you can do with an old thesis is post it online yourself. If you have a website, stick it there as a link. Maybe then a search engine can find it directly, without having to go into the tissues and organs of a university website.

But when I looked at my thesis, I realized it was almost unreadable. It seems inconceivable that this thesis was written by the guy who later produced books that general readers loved, especially Encyclopedia of Evolution and Green Planet. The only thing that made this possible was my subsequent career of teaching, and my continual practice at writing. I had a mission to make science understandable and interesting to students and the general public—and eventually, I learned how.

So I took a couple of days this summer (yes, it was only a couple of days) to rewrite my thesis in plain English. Actually, if I had taken longer, I probably would have gotten bogged down in it and produced a summary less useful to readers. And here’s what I was able to do that I could not in the original:

·         I used plain English, rather than scientific jargonese.

·         I explained the background ideas, which would have been obvious to other experts in the field but which can be presupposed in the general reader.

·         I included photos and stories about the work, showing science to not be some dispassionate truth but to be a very human process, both fun and challenging.

Any of you out there with old theses that nobody looks at—perhaps even you—consider doing what I did. You can read my rewritten thesis on my website.