Bridgeless Gaps

Mark S. Blumberg is a Professor and Starch Faculty Fellow at the University of Iowa.  He currently serves as Editor-in-Chief of the journal Behavioral Neuroscience and as President of the International Society for Developmental Psychobiology.  In his newest book, Freaks of Nature: What Anomalies Tell Us About Development and Evolution, Blumberg takes a subject that is often shunned as discomforting and embarrassing and manages to shed new light on how individuals-and entire species- develop, survive and evolve.  In the original post below commemorates Richard Goldschmidt’s death by celebrating his work.

As we approach the bicentennial of Charles Darwin’s birth, I would like to take a moment to commemorate the anniversary of the death of another great biologist. Richard Goldschmidt, one of the preeminent geneticists of the twentieth century, died fifty years ago at the age of 80. When I was in graduate school, his name had become synonymous with foolishness. Indeed, one did not mention his name without the requisite acknowledgement that his views — especially his notion of the ‘hopeful monster’ — were anathema. I now look back on my eager acceptance of this judgment with a bit of shame. But there is plenty of shame to go around.

Goldschmidt’s seminal volume, The Material Basis of Evolution, was reissued in 1982, 42 years after its original publication. In reconsidering Goldschmidt’s legacy in a review of that reissue, published in Paleobiology, Guy Bush related graduate school experiences that were very similar to my own: when Goldschmidt’s name came up, Bush wrote, “it was inevitably in the context of ‘hopeful monsters’ and to the accompaniment of subdued snickers and knowing nods. It didn’t take long to learn that Richard B. Goldschmidt was not to be taken seriously as an evolutionary biologist…. These early impressions were reinforced by repeated ridicule of Goldschmidt both in print and in conversations with other biologists. I now wonder how many of those who criticized him so authoritatively really read any of his book or papers.”

Bush titled his review “Goldschmidt’s Follies.” Stephen Jay Gould, who penned an introduction to the reissue of the The Material Basis of Evolution, titled his piece “The Uses of Heresy.” Clearly, Goldschmidt had stepped on some toes — and those toes belonged to those individuals who were promoting the so-called Modern Synthesis. Among these promoters were Ernst Mayr and George Gaylord Simpson, two eminent scientists whose graduate class it was where Guy Bush’s early impressions about Goldschmidt were formed.

The Modern Synthesis, which grew rapidly in stature during the 1930 and 1940s, was a critical development in evolutionary thinking as it linked the Darwinian commitment to small, incremental change with the specific details of Mendelian genetics. Goldschmidt’s “heretical” willingness to entertain the possibility of rapid evolutionary change was, therefore, a threat to a key Darwinian tenet. So Goldschmidt had to be crushed; and he was — mercilessly and effectively. To this day, despite his many seminal and undisputed contributions to science, his name and legacy remain banished in limbo.

Among Goldschmidt’s many contributions was his in-depth examination of phenocopies (his term), which are ‘mutant phenotypes’ produced without genetic change through alterations in the developmental environment. These and other critical contributions provide adequate support for the notion that Goldschmidt was hardly the loon that Mayr and others made him out to be. Of course, even Goldschmidt’s fans, including Gould and Bush, recognize his missteps; but scientific perfection has never been a requirement for respect. Darwin’s gemmule hypothesis does not dampen our enthusiasm for his brilliance; and Mayr, rightly revered by the time of his death a few years ago at the age of 100, was not able to escape the occasional doozy — although he did manage to escape the kind of ridicule that he had earlier heaped on Goldschmidt.

Unlike Mayr, who had little appreciation for development, Goldschmidt was particularly attuned to the significance that developmental rate, timing, and patterning mean for the individual and the species. In his words: A “genetic change involving rates of embryonic processes does not affect a single process alone. The physiological balanced system of development is such that in many cases a single upset leads automatically to a whole series of consecutive changes of development in which the ability for embryonic regulation, as well as purely mechanical and topographical moments, come into play; there is in addition the shift in proper timing of integrating processes. If the result is not, as it frequently is, a monstrosity incapable of completing development or surviving, a completely new anatomical construction may emerge in one step from such a change.”

This passage, like so many others, is nuanced, sophisticated, and surprisingly modern. But that single phrase — ‘in one step’ — was heresy to too many. Nonetheless, Goldschmidt saw no other way to account for the “bridgeless gaps” that he believed to separate individual species. Nor was he alone. A half-century earlier, William Bateson had also rejected the exclusive focus of the Darwinians on incremental change. And still others, like Goldschmidt and Bateson, emphasized the need to integrate developmental perspectives into evolutionary thought. Gavin de Beer, Walter Garstang, and Pere Alberch developed similar perspectives. Indeed, it is a curious fact of history that scientists with a background in development and embryology have been less enamored of the Neo-Darwinian commitment to incrementalism and population genetics. Thus, for most of the twentieth century, these evolutionary camps were also separated by a bridgeless gap.

But that gap is shrinking as development creeps steadily back into the evolutionary mainstream. Alas, Goldschmidt may still be too controversial to get any credit. For example, I recently read a scientific paper, published in 2005, that in every way evoked Goldschmidt’s ideas about rapid evolutionary change. However, there was no reference to Goldschmidt at all, but for a curious reference in the final paragraph to “the material basis of evolution,” exactly duplicating the title of Goldschmidt’s infamous book. Assuming that this author knew what he was doing, can it be that he felt comfortable only with a surreptitious acknowledgement of Goldschmidt’s influence? This suggestion hardly seems far-fetched when we consider the visceral responses that Goldschmidt and his ideas still evoke. For example, after Olivia Judson wrote a blog in The New York Times entitled “The monster is back, and it’s hopeful,” Jerry Coyne quickly shot back with a sharp rejoinder. The many comments from readers of these blogs were no less heated.

It is difficult to navigate such disputes, especially when there are so many threads coursing through each argument. As with any such complex issue, agreement and disagreement can flow with each passing sentence. But, in the end, what has become clear to me is that these disputes are too firmly wedded to old facts and fading personalities. If we wish to bridge the gaps between today’s various evolutionary camps, we might want to look to the developing embryo for inspiration. Yes, we have been shaped by past disputes, but that does not mean that each generation is doomed to repeat them without modification.