Native Plants, Habitat Restoration, and Other Science Snippets from Athens, Georgia

Friday: 23 September 2005

Musings on Deduction, Hypothesis, and the Thrill of Prediction  -  @ 05:26:34
Arthur Conan Doyle's Sherlock Holmes was a whiz at deduction, as probably everyone knows. He had an uncanny knack of noticing the smallest details and coming up with a deduction that explained them, and as we all know, he was always right. Poor Sherlock, he never enjoyed the thrill of the last part of the process - making a prediction and then testing it and finding it wrong - he was always right!

This is what scientists do, of course, and really it's what we all do when we solve some kind of problem, whether we realize it or not. A scientist engaged in his or her own specialty involving some unexplained phenomenon will read everything available, do some puttering around in the lab seeing what happens, and then come up with a statement that summarizes her explanation for what she's seeing. If it's worded carefully, it will be possible for her to test a prediction that follows from her hypothesis, and if she's very brave she'll come up with an experiment that is capable of disproving her explanation. If she can't disprove the statement and it still stands, it's well on the way to becoming a valid explanation.

All good scientists, and many normal people, : - )  do exactly this sort of thing, and if you're attentive to the process then it is truly a thrill when a prediction addresses the issue. It's almost unfair to pick out three people and describe in more detail the process they went through, but these three people came up with explanations that not just rocked the scientific world but provided an inspiration to all people who love to think and test out their predictions.

Of course tons have been written about all these people and I can't add substantively to it, but I'm going to muse a little bit on the matter of thinking.

Mention Charles Darwin and you'll get a whole host of responses: "survival of the fittest" or "discovered evolution" being among the most common. Darwin did not exactly discover evolution; by the mid-1850s, he explained one way by which it occurred and in that way greatly refined the understanding of it. Natural selection was the mechanism that he proposed as likely to be the major motivator behind evolution; he admitted and discussed the possibility of others. Common descent was his deduction, and natural selection was the mechanism he hypothesized to drive it.

What is particularly interesting is a prediction that arose from Darwin's explanation: all organisms on Earth - humans, bacteria, cats, sunflowers, sponges, mushrooms - we're all related. *SHINE* For those who can get beyond the ickies, it's a marvelous feeling to know that everything living around us is a relative. I myself find it an absolutely potent thought, among the most ethic of thoughts. For those who can't, well, I'm truly sorry. You have an empathetic disorder.

It took more than a century to confirm his prediction directly, but the analysis of DNA sequences, the commonality of the genetic code, and the universal presence of certain basic types of molecules all show that the prediction that arose from Darwin's hypothesis was, way beyond any reasonable doubt, correct.

Gregor Mendel, who lived about the same time as Darwin, is often called "The Father of Genetics", but he just squeaked by. If his work hadn't been re-discovered half a century later, the Dutch botanist Hugo De Vries would have been The Father. Mendel spent years setting up lines of pea plants that had certain characteristics, and then did crosses between lines and observed what happened. He deduced that there must be two factors in each of his pea plants that controlled a given characteristic - his "First Law." Without any knowledge of DNA, no electron microscope, no knowledge of meiosis, and no modern techniques, he predicted what we today call genes, and further hypothesized that there were two of them for each trait, something we recognize when we view ourselves as diploids. *SHINE*

As far as I know, Mendel didn't write about any observations that invalidated his second great observation and hypothesis: that two traits were inherited independently of each other - his "Second Law". There's been a considerable amount of discussion on the likelihood that Mendel "fudged" his data, but at least with regard to this he seems to have only presented the results that supported his hypothesis. Pea (Pisum sativum) has seven unique chromosomes in its haploid set (14 total, of course, it's a diploid, just like us!), and it turned out that each of the traits that Mendel focused on were controlled by a pair of genes essentially each on a different chromosome. What is the probability of this happening randomly? Why, 1 out of 7!, that is, 1 out of 5040. Had he pursued the less tractable data that probability shows he must have observed, he would have also predicted the presence of chromosomes, the process of recombination much later explained by Thomas Hunt Morgan, and done it without a microscope. Ars longa, vita brevis.

(Parenthetically it should be emphasized that this is not "fudging" of data, as in changing numbers. This was selection of the clean set of data, a lesser offense and one engaged in by many, if not most, if not all, scientists.)

The third individual is Barbara McClintock. Class, raise your hands if you know who Barbara McClintock was. No? Well, ok, I'll tell you - she is one of my heroes. She was a "small scientist", like many of us, who, in the mid 1900s, pursued a passion for years to its ultimate conclusion. She didn't receive huge funding, she wasn't pursued by big money, she didn't have and probably never could have gotten huge numbers of grad students (unless of course the fickle little bastards could have known in advance that she would become a Nobel Laureate), she worked essentially alone, and she never become a "helicopter scientist". Far as I can tell she was an extremely modest person who never flagged.

McClintock was a plant geneticist who for decades doggedly pursued an explanation for the observation of unstable genetic traits in corn. Among other things she isolated lines of corn that had well defined but unstable traits - among these were the colors and spotting patterns in the kernels of corn. Some of these lines were always unstable. Some appeared stable unless she crossed them, and then they became unstable. With the aid of electron microscopy as a way to validate her hypotheses she predicted the presence of transposable elements, or jumping genes. The instability, she said, was due to a piece of DNA that became removed from one place and inserted itself into another. When it did this it sometimes interrupted genes that made color in the kernels, and the instability occurred. Moreover she showed that a second gene was necessary - a gene to allow the jumping gene to be removed. This explained her observation that two apparently stable lines of corn could be crossed to produce unstable kids. The instability was there only when both necessary genes, the transposon that moved, and the transposase enzyme that allowed it to be moved.

I've been told that McClintock's writeups of her work were very dense and very difficult to read; perhaps this is true. Whatever the explanation, no one noticed her work particularly until many years later when transposons were discovered in bacteria. As in the case of Mendel, the importance of her years of work was only recognized by the larger genetics community at that later date. She went on to receive for her work the National Medal of Science in 1970, and the Nobel Prize in Physiology or Medicine in 1983, the first woman to receive an unshared Nobel. *SHINE*

I actually had the pleasure of hearing her speak at the 1985 Savannah Georgia Meetings, the First International Plant Molecular Biology Symposium. She was a tiny, elderly woman, and she had difficulty with her microphone - even then she was rather frail. She was probably as obscure in her talk as she was in her earlier writings. She was wonderful. The audience of around fifteen hundred listeners was utterly charmed.

(And obceleb: a very young Joshua Bell performed in an evening entertainment (was it the Mendelsohn Violin Concerto? I believe it was.) - he became very pissy when some of the more nekultura members of the international audience clapped in-between movements. Oh well, I suppose he's more grown up now, 30 years later.)

Has this turned into a tribute to one small person from another? Yes, I guess it has.

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