Myths in Biology: Mendel's Pea Flowers

At P.Z. Myers' blog, Pharyngula, he has a post on the subject of "myths" in biology, using the number of cell types in humans as an example. He cites Stephen J. Gould's famous article on fox terriers as an example of such myths and how they get incorporated in the science of biology.

You want myths in biology? Pick up any introductory biology textbook and look up Mendel’s original experiments with garden pea plants. Look at the color illustration of the seven phenotypic characters Mendel supposedly tested. Is purple versus white flower color in the figure? Now, read Mendel’s paper describing the seven different characters in garden peas that he studied (you can find the original paper here, in the original German and in English translation). Is purple versus white flower color in the list of characters tested? Interesting…

Toward the end of the paper, Mendel mentions that in a later set of experiments he tested flower color and found the same ratios that he found with the original seven traits he tested. According to the paper, he tested “violett-rothe und weiss Blüthenfarbe” (i.e. “violet-red and white blossom color”), but this test was NOT in his original set of seven experiments, which are the ones always illustrated in biology textbooks.

So, when did biology textbooks start this particular myth? As far as I can tell it was in the first biology textbook with full color illustrations: William T. Keeton’s Biological Science, 2nd ed. The illustrator thought he could kill two birds with one stone by illustrating the technique used to ensure controlled fertilization (i.e. removing the stamens from the flowers using iris scissors) and purple and white flower color. Except that Mendel didn’t study purple versus white flower color in his original series of seven crosses.

Which pair of traits did Mendel actually study, but were replaced by purple versus white flowers in all introductory biology textbooks? The color of the seed-coat, in which gray-brown is dominant and white is recessive. According to Mendel’s original paper, gray-brown seed coats are associated with (what we would now refer to as linked with) “violet-red blossoms and reddish spots in the leaf axils,” but once again Mendel did NOT explicitly test purple versus white flower color in the experiments for which he is remembered, and for which the science of “Mendelian genetics” is named.

And why is the clearly incorrect list (and colored figure) of the seven traits Mendel supposedly studied included in every introductory biology textbook today? Because Keeton’s textbook was the most widely used textbook in biology for decades, so all of the other publishers simply copied what was in his textbook as a way of gaining market share.

Can this myth be corrected now? How many professors’ sets of lecture notes and PowerPoint slides would have to be changed to correct this mistake, and how many textbooks would need new illustrations that included the correct list of the seven traits, and how many people would complain about these changes, or (even worse) suggest that Mendel really did study purple and white flower color in his original series of seven experiments?

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As always, comments, criticisms, and suggestions are warmly welcomed!

--Allen

The Metaphysical Foundations of Modern Science

I started attending the weekly meetings of the Ithaca Friends Meeting in September, 1969. One of the people who made an immediate and lasting impression on me was an older gentlemen, always impeccably dressed, who sometimes spoke in meeting in a quavery, but very determined voice. His "messages" were always very literate, but not necessarily complicated. I was eventually introduced to him, and learned that his name was "Ned" Burtt, and that he was one of the founders of the Ithaca meeting.

After several years we became good friends, but only in the context of the Friends Meeting. I got to know his wife, Marjory, with whom I had many very engaging conversations. She was a retired psychotherapist with an interest in Eastern philosophy, especially Buddhism. I didn't have as many conversations with Ned, not because he wasn't willing, but because he was almost completely deaf. Indeed, after a few years I noticed that Marjory and some of his older friends took turns sitting next to him in meeting, and when someone rose to speak, would write down what they said on a slip of paper and pass it to Ned.

Year later I was co-teaching a course on the history and philosophy of science, for which the teaching staff had chosen as one of the required readings a "classic" in the history of science, The Metaphysical Foundations of Modern Science, by Professor Edwin Arthur Burtt, the Susan Lynn Sage Professor of Philosophy at Cornell University. Translated into dozens of languages and continuously in print since 1924, Burtt's Metaphysical Foundations was often mentioned as the precursor to Thomas Kuhn's The Structure of Scientific Revolutions, and one of the seminal texts in the history of science.

Imagine my surprise (and chagrin) when I discovered that "Ned" Burtt of the Ithaca Friends Meeting was Prof. Edwin Arthur Burtt himself, author of the Metaphysical Foundations and perhaps the most famous historian of science in the first half of the 20th century. Characteristically, he never mentioned it in any of our conversations (brief and halting as they were), and no one else in meeting seemed to think it important enough to mention either.

Ned died in 1989 at the age of 97, and was memorialized at the Ithaca Meeting in our usual way – a silent meeting, punctuated by a few heart-felt "messages" from his friends. I think of him now as I am re-reading once again his Metaphysical Foundations, and am once again struck by his keen insight and masterful use of language. Here's just one sample:

"The glorious romantic universe of Dante and Milton, that set no bounds to the imagination of man as it played over space and time, had now been swept away. Space was identified with the realm of geometry, time with the continuity of number. The world that people had thought themselves living in – a world rich with colour and sound, redolent with fragrance, filled with gladness, love and beauty, speaking everywhere of purposive harmony and creative ideals – was crowded now into minute corners in the brains of scattered organic beings. The really important world outside was a world hard, cold, colourless, silent, and dead, a world of quantity, a world of mathematically computable motions in mechanical regularity. The word of qualities as immediately perceived by man became just a curious and quaint minor effect of that infinite machine beyond. In Newton the Cartesian metaphysics, ambiguously interpreted and stripped of its distinctive claim for serious philosophical consideration, finally overthrew Aristotelianism and became the predominant world-view of modern times.

*Whew* - talk about a splash of cold water in the face. It is this world-view – the one that forms the basis of all of modern science, including biology – that depresses and terrifies those who cannot live without the "old magic" and motivates those who want to tear down "modern" science and go back to the pre-scientific world-view, what Carl Sagan called "the demon-haunted world." But, just like the magic realm of childhood, there is no going back now, not to the innocent and often terrifying universe of the childhood of our cultures. In the words of Bertrand Russell (one of Ned Burtt's contemporaries):

"That Man is the product of causes which had no prevision of the end they were achieving; that his origin, his growth, his hopes and fears, his loves and beliefs, are the outcome of accidental collections of atoms...that all the labours of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system, and that the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins...only on the firm foundation of unyielding despair can the soul's habitation henceforth be safely built." – A Free Man's Worship [1923]

And so tomorrow (it's Memorial Day once again), I will go walking through the little grave yard out behind the Hector Meeting House where Ned and Marjory are buried, and think once again about the old, deaf gentleman whose messages were so eloquent and whose view of reality so unflinching.

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As always, comments, criticisms, and suggestions are warmly welcomed!

--Allen