Mendel in the Hot Seat, 1902

Raphael Weldon’s critiques of Mendelian principles were 100 years ahead of his time.

By | February 1, 2016

LIKE PEAS IN A POD: This photographic plate from Raphael Weldon’s 1902 article displays the spectrum of pea color variation as a critique of Gregor Mendel’s binary categorization of yellow and green. Images 1–6 display the color range of pea seeds of the variety Telephone as sorted by Weldon after removing their seed coats. Images 7–12 display a color scale from the pea variety Stratagem with coats removed. Images 13–18 show color variations in the two cotyledons of the same pea (Telephone variety). Images 19–24 display peas in their seed coats, which mask any color differences between cotyledons (19–20 are of the Telephone variety; 21, Telegraph; 22, Stratagem; 23, Pride of the Market; and 24, Early Morn).
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At the turn of the 20th century, Gregor Mendel’s seminal 1866 paper on pea plants and the principles of inheritance resurfaced in the scientific community, thanks to a few intrepid botanists who had arrived at similar conclusions in their own research. Examining the findings reported in Mendel’s long-buried paper, Walter Frank Raphael Weldon, an Oxford University zoologist at the time, found himself embroiled in controversy.

Weldon had excelled at statistically analyzing variations in wild populations of crabs, shrimps, and snails, and was well-equipped to take a measured look at the Mendel mania occurring among his contemporaries. “[Mendel’s work] was very exciting—even potentially holding the key to a new quantitative science of inheritance,” says Gregory Radick, a science historian and philosopher at the University of Leeds. “But the closer Weldon looked at it, the more skeptical he grew.”

Weldon wrote to commercial pea-plant breeders asking to see samples of their crops for comparison with Mendel’s descriptions. Mendel had focused on traits he designated as binary—seed color was either yellow or green, coats either round or wrinkled. Weldon, however, found much more variety. “Unless you were already con­vinced by Mendel, there was no reason at all to categorize the visible traits in just those two kinds of categories,” says Radick, who detailed Weldon’s work in Science last fall (350:159-60, 2015).

Weldon also took a hard statistical look at Mendel’s data, and the analysis only added to his suspicion. Even if Weldon assumed Mendel’s predictions were accurate, the data were just too good to be true—the equivalent of flipping a coin 100 times and getting exactly 50 heads and 50 tails.

In 1902, Weldon published his critiques in Biometrika, a journal he had cofounded the previous year. According to Radick, Weldon considered Mendel’s data symptomatic of the wider problem with binary categories, which construct a misleading concept of genetic dominance. “Weldon’s confirmed view was that biological science was just on the verge of breaking through to the next level because it was taking variation so seriously,” says Radick. “But it all depended on researchers who were not satisfied with a fictional idealization of complex data—which is, in his mind, what you’re dealing with when you’re dealing with ‘yellow.’ ”

For Weldon, Mendel’s patterns represented special cases where humans had artificially bred out variation in domestic plants and animals. But his paper was met with harsh criticism from a colleague, William Bateson. Former schoolmates, Weldon and Bateson suffered a falling out in the mid-1890s after a series of scientific disagreements. Their rivalry continued through the early 1900s, when Weldon started to write a book detailing his thoughts on Mendel—but Weldon died unexpectedly in 1906 at the age of 46. Bateson continued to champion Mendelian principles and garnered widespread acceptance of rules still taught today in the opening chapters of genetics textbooks.

“Weldon gets remembered, if at all, as the one who misguidedly obstructed the path to Mendelism,” says Radick. “The winners write the history.” But Weldon’s ideas and his unfinished book, stored in the archives at University College London, suggest an alternative path that the early study of genetics might have taken—one that would have more closely approached a modern understanding of DNA’s complexity, embracing variation and unexpected results as crucial to the system rather than exceptions. 

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Avatar of: mightythor


Posts: 80

February 22, 2016

Mendel is the poster child for simplicity in scientific explanation.  His insight led to an understanding of the mechanism of inheritance.  It is doubtful if Weldon's more nuanced parsing of the data would have done so.  Mendel is the Kepler of genetics.  Weldon is its Ptolemy.

Avatar of: bensabio


Posts: 10

February 22, 2016

Color photographs from 1902?  That needs as much explaining as Mendel's data!

Avatar of: JonRichfield


Posts: 132

February 23, 2016

Without the slightest intention of criticising Weldon's acuity, insight or competence,  I am sceptical that early adoption of  his views would have caused a rapid advance in genetic insights; it possibly even might have delayed advances.

For one thing, even early twentieth-century mainline geneticists were already making conceptual advances into polygenic inheritance. For another, the adoption of formal probabilistic and statistical disciplines unavailable to Mendel, were almost immediately applied in genetical work as one of the major fields of biometry; this meant that biological interpretations of genetic effects soon became fairly hard-nosed. Even before WWII, the likes of Fisher had laid the foundations of neoDarwinism. 

Granted, like any other statistics, genetic biometry is a GIGO discipline, and preconceptions did cause a good deal of nonsensical research, but a huge amount of constructive biological discovery and agricultural breeding proceeded apace, aided by microscopical cytology and studies of model organisms such as suitable fungi and  Drosophila, and by field work.

Preconceptions are always with us, and it took the genius of  the likes of McClintock to break some of our conceptual log-jams, and advances in molecular biology to open new fields of insight. (And look how long those took!) We still are finding our feet with many of them, both practical and conceptual. But how Weldon's opinions in his day would have hastened progress is hard to imagine. By complicating our naive views of the day, he might well have delayed or diverted our progress in understanding genetic mechanisms instead of hastening it.

Sometimes it is better to start with simplistic ideas if an idea needs to spread and become established, rather than starting with a thousand ifs ands and buts. I am sorry for Weldon in his day, but am uncertain how bad his effective silencing was for the field.


Avatar of: bensabio


Posts: 10

February 25, 2016

Seriously, if the subtle color differences in those photographs were essential to Weldon's argument, can anyone explain how the plates were produced in 1902?  Were they hand-painted and then reproduced by a color printing method of some kind?  Perhaps the author of this article, or someone else, can respond to this interesting question.  Thanks.

Avatar of: xtsam


Posts: 8

February 26, 2016

Lucky Mendel, otherwise Pubpeer and Retraction Watch would have been all over the place.

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