The buffet and the sushi conveyor

The return of mutationism to mainstream evolutionary biology is evident in the way mainstream articles now describe the role of mutation in evolution, in our reliance on mathematical models that evoke a mutationist view, and in evo-devo research programs that focus on identifying causative major-effect mutations.

This shift has happened in a kind of sub-conscious way, without commentary or reflection.  I’ll comment below on the reasons for that.

My main purpose here is to contrast way that the neo-Darwinian and mutationist views refer implicitly to two different regimes of population genetics evoked in two styles of self-service restaurant: the buffet and the sushi conveyor.

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Why size matters: Saltationism, creativity, and the reign of the DiNOs

Debates on “gradualism” in evolutionary biology address the size distribution of evolutionary changes.  The classical Darwinian position, better described as “infinitesimalism”, holds that evolutionary change is smooth in the sense of being composed of an abundance of infinitesimals (not one infinitesimal at a time, but a blending flow of infinitesimals).   The alternative is that evolution sometimes involves “saltations” or jumps, i.e., distinctive and discrete steps.  The dispute between these two positions has been a subject of acrimony at various times in the 20th century, with several minor skirmishes, and a larger battle with at least one genuine casualty (image).

Walter Frank Rafael Weldon (public domain image from wikipedia). Legend has it that Weldon ignored an advancing illness and worked himself to death trying to disprove the relevance of Mendelism in natural inheritance.

Walter Frank Rafael Weldon (public domain image from wikipedia).  Weldon ignored an advancing illness and worked himself to death (1906) poring over breeding records in an attempt to cast doubt on discrete inheritance.  Along with Pearson and other “biometricians”, Weldon held to Darwin’s non-Mendelian view combining gradual hereditary fluctuations with blending inheritance.

Today, over a decade into the 21st century, we have abundant evidence for saltations, yet the term is virtually unknown, and we still seem to invoke selection under the assumption of gradualism.  Are we saltationists, or not?  I’m going to offer 3 answers below.

But first, we need to review why the issue is important for evolutionary theory.

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Mendelian-Mutationism: the Forgotten Evolutionary Synthesis

What is Mendelian-mutationism?  And why do we argue in a recent paper in that it represents a forgotten evolutionary synthesis (Stoltzfus and Cable, 2014, Mendelian-Mutationism: The Forgotten Evolutionary Synthesis. J Hist Biol. doi:10.1007/s10739-014-9383-2)?

ys01-popsize

Effect of mutation bias in the 1-step adaptation model of Yampolsky & Stoltzfus, 2001. The greater the bias in mutation, the greater the tendency to evolve in the mutationally favored direction.

For me, the story started a long time ago with our theoretical demonstration (graph at right) that bias in the introduction of variation (by mutation-and-altered-development) is a fundamental cause of non-randomness in evolution (Yampolsky & Stoltzfus, 2001).

The novelty of this claim bothered me deeply.  Why?  Here was a basic principle— a causal link between non-randomness in biological inputs (mutational and developmental biases) and non-randomness in evolutionary outputs— as fundamental as the concept of selection or drift.  Yet, this principle was not mentioned in any textbook of evolution or population genetics (indeed, there is even a classical population-genetic argument against a determinative role for mutational biases).  I could not even find this principle in the research literature!  When it comes to contemplating the impact of biases in variation, evolutionary biologists habitually assume that such an impact is impossible, except in the special case of (1) rigid constraints (i.e., the impossibility of generating form B means we’ll get A or C instead), or (2) neutral evolution.   We knew that all of this was incorrect.

This prompted 2 questions.  Why wasn’t a general connection between biases in variation and biases in evolution recognized long ago, e.g., by Wright, Haldane or Fisher?   And, why— after it was discovered and published in 2001— didn’t this inspire a revolution?

bookshelf

The top of my evolution bookshelf, with historic works in roughly chronological order: from Darwin and Mivart to the Mendelians (top shelf), then the core of the Modern Synthesis, up to the early molecular era (next shelf) [1]

I’m still puzzling over the second, admittedly naive, question.  To address the first question, I’ve spent an inordinate amount of time studying the development of evolutionary thought (bookshelf at right).

The short answer is this: the notion that mutation has a dispositional role in evolution, influencing its rate and direction, represents a kind of “internal” causation, an internal source of direction in evolution, that Darwin’s followers rejected as illegitimate.  Ever since, it has been a blind spot in evolutionary thinking.

The nature of this rejection is hard to comprehend today, due to a process of amnesia and theory-drift.  Nearly all evolutionary biologists today believe that evolutionary biology has a prevailing theory, and that this theory— called the Modern Synthesis or modern neo-Darwinism— came together in the mid-20th century.   What few realize is how far the common conception of this theory has drifted from its original intentions.  The original Modern Synthesis was held together with Darwinian doctrines that most scientists today do not accept, such as the doctrine of gradualism, the idea that selection is creative, or the rejection of any internal causes of direction.  We can think of these as the “soft parts” of the Modern Synthesis, the muscles and connective tissue that gave it shape and motion.

whale-bones

The soft bits of this whale carcass rotted away, leaving only the bones.

Over time, the Darwinian character of the Modern Synthesis has rotted away, leaving only the more resilient parts.  This is why scientists today think of the Modern Synthesis as a kind of open-ended framework for understanding evolution. They are looking at an open-ended skeleton.

Our study of early geneticists revealed that this skeleton predates the Modern Synthesis.  There was an earlier Mendelian-Mutationist Synthesis that combined mutation, heredity and selection, without Darwinian doctrinal commitments to gradualism, the creativity of selection, and the “randomness” (non-importance) of mutation.  What most scientists today think of as the Modern Synthesis is actually the forgotten Mendelian-Mutationist synthesis. Like scientists today, the early geneticists or “mutationists” welcomed both selection and neutrality, allowed both gradual change and saltations, and welcomed the idea that biases in mutation could be the cause of parallelisms or trends.

The new paper by Stoltzfus and Cable describes what the early geneticists believed about how evolution works, and what they contributed to the foundations of evolutionary thought.  It also explains why they rejected Darwin’s theory (another case in which the popular conception of a theory today does not match what its historical meaning).

But that’s only half of the story.  The other big theme is historiography, the telling of history.  The disconnect between what actually happened and what scientists believe is not just a matter of theory-drift.

“History is written by the victors,” Churchill said.  In this case, the victorious architects of the Modern Synthesis promulgated a view of early geneticists as bumbling fools who saw mutation and selection as opposing principles, and who couldn’t think synthetically.  The period of 1900 to 1920, actually a rich period in which early geneticists laid the foundations of modern evolutionary thought, is described perversely as part of an “eclipse of Darwinism”— a period of darkness when the world was deprived of His light— lasting until Darwinism is re-born in the Modern Synthesis.  This story-telling has been so influential that, when contemporary scientists list historically important figures, all key figures of the Mendelian-Mutationist synthesis are removed, Soviet-style (see figure below).[2]

evotmline_with_box

On this timeline of “notable people who have contributed to evolutionary thought” (source), I have super-imposed a salmon-colored box. This box includes the birth year of anyone 25 to 60 years old— the prime of a scientist’s life—  when genetics was discovered in 1900.  No timelines begin in the box. That is, the figure tells us there were no notable contributions by scientists born in this period, which includes the birth of de Vries (1848-1935), Johannsen (1857-1927), Bateson (1861-1926), Cuénot (1866-1951), Davenport (1866-1944), Morgan (1866-1945), and Punnett (1875-1967). Richard Goldschmidt (1878-1958), born just a few years later and listed as a non-Darwinian (top), was a second-generation mutationist whose 1940 book introduced “hopeful monsters” and provoked Ernst Mayr into writing a book of his own.

That is, the distorted view of history that evolutionary biologists hold today is not just a matter of passive amnesia, but of a highly successful public relations campaign, what evo-devoist Stuart Newman recently called “an unremitting 90-year campaign to identify ‘evolutionary theory’ with ‘Darwinism'”.

The recent paper on Mendelian-Mutationism is actually an off-shoot of a series of “Mutationism myth” blogs written for SandWalk in 2010.  To turn the blogs into a scholarly work worthy of publication in a peer-reviewed historical journal was a major project accomplished over the course of 2 years, by teaming up with a history-of-science graduate student named Kele Cable. Kele recently blogged about our paper on his web site.

Notes

[1] Some of my favorites: Haldane, 1932 (the tattered volume, top, second from right); the 1911 (3rd) edition of Punnett’s Mendelism, the first textbook of genetics (the slimmer of two burgundy volumes, top center); George Williams (1966) Adaptation and Natural Selection (row 2, 9th from right, with the shiny jacket cover); Lewontin, 1974 (row 2, right end, red with gold lettering next to Crow & Kimura 1970).

[2] Other examples could be given.  The Oxford Encyclopedia of Evolution (click for searchable online index) has an entry for Mendel, who made no direct contributions to evolutionary thinking, but lacks an entry for all of the mutationists except for Morgan.  Importantly, the entry for Morgan says nothing of his evolutionary views, only of his contributions to genetics.  Textbooks (e.g., Ridley, 1993, or Freeman & Herron, 1998) and online teaching materials (try a web search on “development” or “history”  of evolutionary thought) frequently jump from Darwin to the Modern Synthesis, with the explanation that Darwin’s theory was right but needed a mechanism, and this was supplied when the architects of the Modern Synthesis combined genetics and selection.  Early geneticists, if they are mentioned at all, are depicted only for their alleged failure to understand selection, accept small changes, or achieve synthesis.

When “Darwinian adaptation” is neither

Getting stuff right

Early in the evolution of the Sequence Ontology, it was noted (by gadflies like myself) that SO asserts the relationship of mRNA to gene to be the “part of” relationship.  This is obviously wrong.  An RNA molecule is not part of a DNA molecule.   Saying that mRNA is part of a gene is like saying that a CD with some audio chapters from a book is part of that book.

Ontologies are supposed to support formal reasoning: errors in representation will lead inevitably to erroneous results.  For instance, if we are reasoning about the chemical composition of a cell using mRNA part_of gene as a constraint, we would conclude falsely that the mass of DNA must always be at least as much as the mass of mRNA, because the mass of a thing is always at least as great as the mass of some specified parts.

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The Mutationism Myth (1): The Monk’s Lost Code and the Great Confusion

This is the first in a series of blogs first published in 2010 on Sandwalk.

The mutationism myth tells the story of how, just over a century ago, the scientific community responded to the discovery of Mendelian genetics by discarding Darwinism, and how Darwinism subsequently was restored.  In this, the first of six parts, we are not going to confront any tough scientific or conceptual issues. Instead, we are just going to review an odd story about our intellectual history.

The Mutationism Story

While “myth” has the connotation of falsehood, the story that a myth tells isn’t necessarily a false one. The mutationism myth, at least, is anchored in historical events.1

The mutationism myth tells the story of how, just over a century ago, the scientific community responded to the discovery of Mendelian genetics by discarding Darwinism, and how Darwinism subsequently was restored. The villains of the story are the influential early geneticists or “Mendelians” who saw genetics as a refutation of Darwinism; the heroes are first, the founders of population genetics, theoreticians who sorted everything out in favor of Darwinism by about 1930, and second, the architects of the Modern Synthesis, activists who popularized and institutionalized what we’re calling “Darwinism 2.0”.

This story has been re-told in secondary sources for nearly 50 years, though I sense that the frequency is decreasing as this episode passes into ancient history. To find examples, try looking up “mutationism” (sometimes “Mendelism” or even “saltationism”) in the index of a book about evolution.

I encourage you to consult whatever sources you have and to share the stories that you find. Note that you won’t always be successful. A quick survey of several dozen contemporary books on my shelf reveals that most don’t address this episode specifically (a notable absence, in some cases 2); some tell the mutationism myth with varying degrees of panache; and a few provide a historical account rather than a myth. The few historical accounts that I found were in Gould’s 2002 The Structure of Evolutionary Theory, Strickberger’s 1990 textbook Evolution, and the Wikipedia entry on “Mutationism”.

Sample stories

Lets look at a few examples of the mutationism story. Readers who want to check out a freely available online source from the scholarly literature may refer to Ayala and Fitch, 1997 (http://www.ncbi.nlm.nih.gov/pubmed/9223250?dopt=Citation). One example that really caught my eye is not from scientific literature, but from the 2005 obituary for Ernst Mayr in The Economist:

It was not that biologists had given up on evolution by the 1940s-quite the contrary. But they had got very confused about its mechanism. . . . The geneticists of the early 20th century did not help. They rediscovered the laws of inheritance first developed 40 years earlier by Gregor Mendel, an unsung Moravian monk. They also discovered the idea of genetic mutation. But instead of linking these things to natural selection, they came up with the idea of “saltation”-in other words, sudden mutational shifts from one well-adapted species to another. Nor, the geneticists complained, had there been enough time for natural selection to do its work, given what they had discovered about the rate at which mutations occur, and the fact that most mutations are deleterious. It was all a bit of a mess. . .Mr Mayr’s advantage over the laboratory-bound biologists who had hijacked and diluted Darwin’s legacy was that, like Darwin, he was a naturalist-and a good one. (anonymous, 2005)

Of course, this is a magazine article, written by anonymous staff writers– typically one doesn’t see such florid language in the scholarly literature. But did the staff writers of the Economist (representing elite opinion) really originate this story, based on their own personal recollections of the 1930’s? Of course not. Mayr himself popularized the image of geneticists as laboratory-bound geeks lacking the organic insight of “naturalists”. This disdain for the geneticists who “hijacked” Darwin’s legacy is readily apparent when evolutionary writers depict geneticists as fools holding “beliefs” that have “obvious inadequacies”, unable to understand or “grasp” their own scientific findings:

“It is hard for us to comprehend but, in the early years of this century when the phenomenon of mutation was first named, it was regarded not as a necessary part of Darwinian theory but as an alternative theory of evolution! There was a school of geneticists called the mutationists, which included such famous names as Hugo de Vries and William Bateson among the early rediscoverers of Mendel’s principles of heredity, Wilhelm Johannsen the inventor of the word gene, and Thomas Hunt Morgan the father of the chromosome theory of heredity. . . Mendelian genetics was thought of, not as the central plank of Darwinism that it is today, but as antithetical to Darwinism. . . It is extremely hard for the modern mind to respond to this idea with anything but mirth” (Dawkins, 1987, p. 305)

“According to mutationism, random changes in the hereditary material are sufficient for adaptation without much, or any, selection at all. Mutations just somehow happen to be adaptive, the right changes simply manage to occur. The inadequacies of this view are obvious” (Cronin, 1991, p. 47).

“Darwin knew nothing of this [i.e., genetics] but as it turned out, his ignorance was sublimely irrelevant to the problem he was really interested in tackling: evolution. This point was not fully grasped by biologists. Many early geneticists at the dawn of the 20th century, thought their discoveries of the fundamental principles of genetics somehow cast doubt [on], or rendered obsolete, the concept of natural selection. It took several decades of experimentation and theoretical (including mathematical) analysis to show not only that there was no conflict inherent between the emerging results of genetics and the older Darwinian notion of natural selection, but that the two operate in different domains.” (Eldredge, 2001, p. 67)

“Mendelian particulate inheritance (today, we call the “particles” genes) was originally identified with De Vries’s “mutation theory”, according to which new variations or species originated in large jumps, or macromutations, and evolution was exclusively explained by mutation pressure. Darwinian naturalists, believing that Mendelism was synonymous with mutation theory, held on to theories of soft inheritance, while they considered selection a weak force at best. They did not know of the new findings in genetics that would have supported Darwinism. (SegerstrŒle, 2002)

Notice how, in every version of the story above, the position taken by early geneticists just doesn’t make sense. This isn’t a story of theory versus theory, its a story of confusion ultimately yielding to reason.

If de Vries and the other geneticists are playing the role of the pied piper in this story, the “naturalists” are like the children lured away from their Darwinian home. Ultimately the innocents are returned, and order restored, by mathematicians:

“Between 1918 and 1932 Fisher, Haldane, and Wright showed that Mendelian genetics is consistent with natural selection. Only then, more than 60 years after the publication of The Origin of Species, was the genetic objection to natural selection finally removed. Modern molecular and developmental genetics have confirmed in exquisite chemical detail the key aspects of genetics necessary for Darwin’s ideas to work: that the genetic material is DNA, that DNA has a sequence, . . . mutates . . . contains information . . ” (p. 16 of Stearns and Hoekstra, 2005)

One might have thought that the compatibility of genetics and selection was obvious from the start, or that it had been demonstrated by the selection experiments of Johannsen, but apparently biologists of the time had a high demand for mathematical rigor.

Anatomy of a Myth

In a subsequent post, we will look at original sources to see what the “mutationists” actually believed, and why. And eventually we will integrate this into the bigger picture of how evolutionary theory developed. But for now, lets just summarize the pattern that is apparent in the literature.

First, the mutationism story is clearly a story or myth, and not an ordinary scientific truth claim. We can see this because the story-tellers are not using ordinary scientific conventions to convince us that the story is true. If you or I were making an ordinary scientific argument (for instance) for an effect of “translational selection” on codon usage, we would mention a correlation between codon frequencies and the abundance of corresponding tRNAs, citing the classic work of Ikemura (1981), and we might even repeat a figure showing this correlation, to impress this point upon the minds of readers (e.g., just as in Ch. 7 of Freeman & Herron, 1998).

When I see instances of the mutationism story, typically I don’t find quotations illustrating what the mutationists believed, nor facts & figures to refute their views, but only vague attributions and generalized claims. Apropos, the following quotation from Ernst Mayr never fails to make me laugh:

The genetic work of the last four decades has refuted mutationism (saltationism) so thoroughly that it is not necessary to repeat once more all the genetic evidence against it. (Mayr, 1960)

And the puissant Dr. Mayr proceeds on, not boring the reader with any tiresome “genetic evidence”, nor citing sources that might allow the reader to evaluate the truth of his statement. Its a story, after all.

By contrast, the 3 sources that I mentioned above as providing scientific history, rather than myth, all make reference to specific experimental and theoretical results, and reveal knowledge of specific historically important scientific works. For instance, Strickberger’s reference list includes Johannsen, 1903, as well as the 1902 paper by Yule that reconciled Mendelian genetics with quantitative variation (in neo-Darwinian mythology, credit for Yule’s work is given to little Ronny Fisher, who was 11 at the time).

Second, every story has a plot or “action”, and the main action of the mutationism story is a turn of fate in which power is temporarily in the hands of the wrong people or ideas. In archetypal terms, its a story of usurpation and restoration: the throne is usurped, and the kingdom falls into darkness and confusion until the throne is restored to the king’s rightful heirs. The mutationism episode didn’t have to be told that way: it might have been presented as a period of reform (in which old ideas were abandoned) or discovery (when new territory was mapped out). Instead, its presented as a mistake, an interlude of confusion, a collective delusion.

Indeed, another way to look at the mythic action is that the Mendelians are wizards or false prophets who place the kingdom under a spell, leading folks astray and causing them to believe things that they just shouldn’t have believed.

What delusional spell did the Mendelians cast? In the story by Eldredge, or by Stearns & Hoekstra above, the spell is that Mendelian genetics is inconsistent with “the concept of natural selection” (Eldredge). In the story told by SegerstrŒle, Cronin, Mayr and The Economist, the delusional spell is a bit different: the principle of selection is irrelevant because mutational jumps alone explain evolution.

Third, the key to restoring Darwin’s kingdom was to add the missing piece of genetics. Ultimately, after the period of darkness ended, the discovery of genetics “provided the missing link in Darwin’s theory” (SegerstrŒle, 2002), or “The missing link in Darwin’s argument was provided by Mendelian genetics” (Ayala & Fitch, 1997). Darwinism was restored, not by taking away the power of genetics, but by redirecting it to support Darwinism. Clearly, genetics is the key to ruling the kingdom, like the One Ring that Rules them All in Tolkien’s world. The ones who have the ring have the power.

The story is made more fascinating by the fact that the key to power is literally a code of rules developed by a monk that remained lost for nearly half a century. The usurpers who discover The Monk’s Code misinterpret it, and use it to overthrow the true king, establishing a reign of error. But when The Founders decipher the true meaning of the Monk’s Code, The Architects campaign throughout the kingdom, spreading the news: the Monk’s Code proves that Darwin is the true king. Darwin’s rule is re-established, all opposition ceases, and the kingdom is unified.

Homework

If you would like to contribute a mutationism story, I would be happy to start a collection if you make it easy for me by providing a complete and well formed text item. Be sure to provide a quoted passage with a source, citing exact page numbers. If we get enough stories, lets try to recruit a sociologist or historian to study this further.

Summary

To summarize, the mutationism story is a myth that is retold in secondary sources. The basic story is simple: the discoverers of genetics misinterpreted their discovery, thinking it incompatible with Darwinism; Darwinism went into disfavor; population geneticists came along and showed that genetics was the missing key to Darwinism; Darwinism was restored and once again reigned supreme.

Next time on the The Curious Disconnect, we’ll start pulling on some of the loose threads of this story.

For now, note how the writers quoted above are genuinely baffled by our scientific history. It just doesn’t make sense to them. A century ago, most of an entire generation of scientists thought of genetics as a contradiction of Darwinism. This is a historical fact, and presumably it has an explanation that rational folks can understand by examining what scientists of the time wrote. But this historical fact mystifies Dawkins, Eldredge, Cronin, and others.

References

Anonymous. 2005. Ernst Mayr, evolutionary biologist, died on February 3rd, aged 100. The Economist, February.

Ayala, F. J., and W. M. Fitch. 1997. Genetics and the origin of species: an introduction. Proc Natl Acad Sci U S A 94:7691-7697.

Cronin, H. 1991. The Ant and the Peacock. Cambridge University Presss, Cambridge.Dawkins, R. 1987. The Blind Watchmaker. W.W. Norton and Company, New York.

Eldredge, N. 2001. The Triumph of Evolution and the Failure of Creationism. W H Freeman & Co.

Freeman, S., and J. C. Herron. 1998. Evolutionary Analysis. Prentice-Hall, Upper Saddle River, New Jersey.

Gould, S. J. 2002. The Structure of Evolutionary Theory. Harvard University Press, Cambridge, Massachusetts.

Ikemura, T. 1981. Correlation between the abundance of Escherichia coli transfer RNAs and the occurrence of the respective codons in its protein genes: a proposal for a synonymous codon choice that is optimal for the E. coli translational system. J Mol Biol 151:389-409.

Mayr, E. 1960. The Emergence of Evolutionary Novelties. Pp. 349-380 in S. Tax, and C. Callender, eds. Evolution After Darwin: The University of Chicago Centennial. University of Chicago Press, Chicago.

SegerstrŒle, U. 2002. Neo-Darwinism. Pp. 807-810 inM. Pagel, ed. Encyclopedia of Evolution. Oxford University Press, New York.

Stearns, S. C., and R. F. Hoekstra. 2005. Evolution: an introduction. Oxford University Press, New York.

Strickberger, M.W. 1990. Evolution (1st edition).

Notes

1 The defining characteristic of a myth is not that it isn’t literally true, but that it isn’t told for reason of being literally true, but for reason of being meaningful or poignant: a myth is a story with a cultural value, not necessarily a literal-truth value. The connection between myths and untruths, then, has to do with discoverability: when we find a pattern P = { X people are repeating story Y }, where X is a large number, this pattern by itself does not prove that Y is a myth because X people might have all discovered or verified Y independently; but if Y has diverse elements that are untrue (or unverifiable), then we can conclude that its repetition does not signify independent verification, suggesting that its a myth.

2The Oxford Encyclopedia of Evolution does not have an article on mutationism; the article on Morgan says nothing of his views on evolution; there is no article on Bateson; mutationism is only addressed peripherally in Hull’s article on the history of evolutionary theory; it is mainly addressed in SegerstrŒle’s article on neo-Darwinism.

Re-reading Provine (1971), part 1

William Provine‘s seminal work of history, The Origins of Theoretical Population Genetics (1971), recounts how the foundations of modern neo-Darwinism were established in the first 2 decades of the 20th century.  Superficially, Provine’s book aligns with the standard triumphalist narrative in which the architects of the Modern Synthesis combine selection and genetics to yield a workable theory that refutes the mutation-driven view of early geneticists.

However, it also has another story to tell.  If we read the book with a critical eye, we’ll find a completely different story that expains why Provine himself, in a 2001 reprinting, said that the synthesis “came unraveled” for him in the period after 1980.

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The Mutationism Myth (6): Back to the Future

This post wraps up a 6-part series on the Mutationism Myth (a more scholarly version of this material ended being published in J. Hist. Biol. by Stoltzfus and Cable, 2014), and sets the stage for the future by locating the primary weakness of the 20th century neo-Darwinian consensus in its theory of variation. (more…)

Mutationism Myth (5): The Restoration

This is the 5th in a series of 2010 blogs entitled “The Mutationism Myth” (a more scholarly version of this material ended being published in J. Hist. Biol. by Stoltzfus and Cable, 2014)

The Mutationism Myth, part 5. The Restoration

In the Mutationism Myth (see part 1), the Modern Synthesis (MS) rescues evolutionary biology from the Mendelian heresy, by showing that genetics is consistent with selection. In reality, the Mendelians had already synthesized genetics and selection (part 3), but rejected Darwin’s errant views of heredity (part 2) and rejected, to varying degrees, the Darwinian doctrines that subordinated the role of variation so as to render selection the ruling principle in evolution. How, then, did the Modern Synthesis restore Darwinism?

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The Mutationism Myth (4): Mendelian Heterodoxies

This is the 4th in a series of 2010 blogs entitled “The Mutationism Myth” (a more scholarly version of this material ended being published in J. Hist. Biol. by Stoltzfus and Cable, 2014)

In this oft-told story (see part 1), the discovery of genetics in 1900 leads to rejection of Darwin’s theory and the rise of “mutationism”, a laughable theory that imagines evolution by mutation alone, without selection. “Mutationism” prevails for a generation, until Fisher, Haldane and Wright show that genetics is the missing key to Darwinism. In the conclusion to the story, the world is set right again when the “Modern Synthesis”, combining selection with Mendelian genetics, shoulders aside the mutationist heresy, which ends up in the dustbin of history with the other “doomed rivals” of Darwin’s great theory.  As we found out in part 2, the Mendelians rejected Darwin’s errant principles of heredity, not his principle of selection. In part 3, we considered aspects of the Mendelian view that became the foundations of mainstream 20th-century thinking.

But this begs another question: if the Mendelians invented the 20th-century consensus, and just left it to others to work out the math, why aren’t they lauded as “founders” of modern neo-Darwinism, instead of being derided as fools? We’ll find out in part 4 (below), and part 5. (more…)