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‘In Weismann’s Footsteps: The Cyto-rebellion of C.D. Darlington’
Oren Harman
Introduction
“The time in which men believed that science could be advanced by the mere
collection of facts has long passed away.”1 Such was the judgment of the ageing,
increasingly cantankerous August Weismann, Germany’s leading biologist, in 1886.
A short four years after the death of Charles Darwin, Weismann was intent on
describing a cellular theory to match the English naturalist’s theory of evolution by
natural selection. “The investigation of mere details,” he wrote, “had led to a state of
intellectual short-sightedness, interest being shown only for that which was
immediately in view. Immense numbers of detailed facts were thus accumulated,
but… the intellectual bond which should have bound them together was wanting.”2
What biology needed more than anything was a stroke of bold theory-making, and
that’s what Weismann delivered: for sexual organisms to beget offspring, there must
exist a special reduction division, otherwise the genetic material would double in each
successive generation.3 Not that Weismann, who was increasingly growing blind, or
anyone else for that matter, had actually seen this division occur. This leap of faith
was based entirely on unassailable genetic logic, and it gave meiosis – a term coined
in 1905 – to the world. It would also render Weismann a hero to a young English
cytologist struggling to figure our what precisely happens during meiosis, some forty
years into the future. We’ll return to Weismann later, but first, let’s leap ahead in time
to the real subject of our story.
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Cyril Dean Darlington (1903-1981) was born by mistake. “My birth gave rise to a
crisis in the family,” he wrote years later. “My mother claimed that she didn’t know
how it happened. My father on the contrary was quite certain. He applied a rule
without formally declaring it that never again would he cohabit with his wife. It was a
rule that he never broke in his remaining forty years. Whether he regarded me as an
accessory to this mishap or misdemeanor I am still not sure.”4 Here, at the very
beginning, was planted the seed of all that was to come. Darlington’s very existence
was from the outset shrouded in doubt. It was far from clear that he was even wanted.
Darlington would show the world, and, especially, his father, that the ‘mishap’ or
‘misdemeanor’ had not been in vain. Darlington was born a rebel.
Alfred, his lone and older brother, was always his father’s favorite. Away from their
Lancashire, and then Ealing, home, fighting the war against the Germans and winning
medals of honor, Alfred’s very existence seemed to accentuate Cyril’s own
uselessness at home. Invariably, he caught the wrath of his dyspeptic father. Mother
was overprotective, and increasingly depressed. Childhood was a sullen, hollow
affair. When he finally graduated from the South Eastern Agricultural College at
Wye, Darlington put in an application for a scholarship to travel abroad, as far away
as possible- to Trinidad, to become a farmer. A tough and cocky outer veneer had
come to characterize his dealings with people. Already he was anti-authoritarian in
the extreme, writing to his father at eighteen: “…nothing galls me so much as to have
other people’s beliefs forced down my throat.”5 But showing no signs of its author
being either a promising student or a terribly talented agriculturalist, Darlington’s
Caribbean application was rejected by the Empire Cotton Growing Corporation.
Disaffected, arrogant, and at wits end, Darlington was cajoled by a master at Wye to
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try the next (and only) best thing: a volunteer position at the John Innes Horticultural
Institution. After all, the only subject that had captured Darlington’s imagination at
Wye had been the new field people were now calling ‘genetics.’ The Innes was
Britain’s premier horticultural institute, but its Governing Council was able to secure
the famous Mendelian William Bateson as its first director in 1910 only by promising
to allow research on genetics as well. “The rewards from genetics are slight,” the
white-haired Bateson pronounced beneath his moustache as he approached a cocky
but frightened Darlington in his carpet slippers in the Institution’s library in the fall of
1923, “only those who attained unheard of heights of achievement can ever hope to
make a living out of it.”6 Uncertain of his direction, but determined nevertheless to
succeed at all costs, Darlington shook the old man’s hand. “Unheard of heights of
achievement” somehow sounded strangely alluring.
Although he didn’t know it, by the time Darlington had arrived at the Innes the once
pioneering Bateson was an ageing director, already surpassed by Thomas Hunt
Morgan and his ‘Fly Room’ group at Columbia University across the Atlantic in New
York. The chromosomal theory of heredity, which postulated that the genes
responsible for heredity lay physically on the chromosomes in the nucleus of cells,
was the lynchpin upon which the success of Morgan’s genetics lay. But Bateson, a
philosophical aesthete who had little time for materialism, denied the role of the
chromosomes in the hereditary process.7 Stubborn yet realistic, Bateson had
journeyed in the winter of 1921-1922 to the United States to see for himself what the
chromosome theory had to offer genetics after all. Impressed and profoundly humbled
he appointed upon return a cytologist, Frank Newton, less as an omen of a complete
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change of mind and more as a fig leaf to cover what looked to be, in the new world of
chromosomal genetics, an embarrassment.
Newton was skeptical of Bateson, and, when Darlington arrived, took him under his
wing, teaching him how to examine hyacinth chromosomes under the old brass
microscope his boss had begrudgingly supplied him. By 1926 Bateson was dead, and
Newton, just 33, succumbed to cancer less than a year after the Director. Left literally
to his own vices and devices, the young Darlington – outwardly overconfident, but
really disguising a deep sense of awe at a mysterious microscopic world entirely
unknown to him, and seemingly very illusive - set out to make his own sense of the
chromosomes and their role in nature. He was now a rebel with a field if not yet a
cause, no matter how at sea or ill-prepared for the fight. “At the age of 18 most of the
world seemed stupid and annoyed me,” he informed his Diary, “at 24 I know it is
stupid and it ceases to worry me.”8 The outrageous confidence would prove valuable.
Within five short years, and working almost entirely alone, Darlington authored
Recent Advances in Cytology in 1932, a book that was to have a profound impact not
only on his own field of cytology, but on genetics, and evolutionary theory as well,
catapulting Darlington to world fame. It would also fashion him one of the greatest
rebels cytology had ever seen.
Recent Advances in Cytology
So what was the nature of Darlington’s rebellion? And what was he rebelling against?
When Darlington turned as an orphaned scientist to look upon the chromosomes, two
problems continued to dominate the silent world of cytology inhabiting the space
between the ocular lens above and the preparation slide below. First, did the
chromosomes pair side-by-side during reduction division (meiosis), or was it end-to-
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end? This was important, for if the chromosomes paired end-to-end, it would be
unclear how they exchanged genetic material between them. The exchange of genetic
material between homologous chromosomes, called crossing over, was presumed to
happen during meiosis, and seemed to be the explanation for much of the variation
begot by each successive generation in nature, and the true benefit of sexuality. In
1909 the Belgian cytologist and Jesuit priest Frans Alfons Janssens had observed
cross-like figures produced by the tangled homologous chromosomes during meiosis,
and called them chiasmata, meaning cross-like. Morgan assumed that Janssens’
chiasmata evidenced the physical crossing over of genes between maternal and
paternal chromosomes, and turned this assumption (it had yet to be proven) into the
very crux of the mapping procedure he and his group developed to suggest that genes
lay physically on the chromosomes. It’s preoccupations small and technical, the
second problem vexing cytology was whether the chiasmata were the result, or rather
the cause of such crossing-over.
Working almost entirely in isolation, Darlington was able within a few short years
to produce an axiomatic account of chromosome mechanics. In three simple laws he
summed up the entire system: (1) All attraction between chromosomes is always in
pairs, and side-by-side, as opposed to end-to-end; (2) Chiasmata are the condition of
orderly pairing and later segregation during meiosis; (3) Chiasmata are always the
consequence of genetic crossing over between homologous chromosomes.
Why was any of this important?
Peering through the lens of a microscope at the tiny world of the chromosomes, it was
the grander questions of an evolutionary nature that Darlington was really after. Only
after the laws of chromosome mechanics were described and understood could their
role in evolution be theorized. In the preface to Recent Advances in Cytology,
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Darlington made clear where all this was leading:
The importance of the chromosome as determining the hereditary
functions has placed them outside the ordinary field of evolutionary
enquiry. They have been considered as the very fount and origin of
adaptive change and therefore not themselves capable of adaptation.
Now they can be shown to be subject to the genetical variation which
they themselves, by changes of their parts, determine.9
In the final chapter, ‘The Evolution of Genetic Systems,’ Darlington outlined these
ideas in full force. Not only did heredity lead to evolution, he argued; heredity itself
was subject to evolution. Morgan and company had shown that genes exist on
chromosomes, like beads on a string, and that they somehow carry the secrets of
heredity. Following this lead, the mathematical population geneticists demonstrated
with little more than pen and pencil that evolution works by nature selecting those
genes that are adaptive and selecting out those genes that are not. Darlington was now
arguing that the chromosomes, far from passive repositories of genes, are themselves
under genetic control, and determine by their movements the relative amount and kind
of recombination of genes occurring in each successive generation. It was this
quantity – the amount and kind of variation produced during meiosis upon which
selection can act – which more than any other variable determined the fate of
organisms and ultimately the origin and propagation of species. Having begun five
years earlier by looking at chromosomes for their own sake, Darlington could now
begin to understand evolution itself largely as a function of their behavior.
Reception
Making cytology relevant to evolution would seem to be a welcome development,
but Darlington’s ideas quickly met unbridled reactions of scorn and indignation.
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Hampton Carson, a young graduate student at the time, remembered the reaction to
Recent Advances of Cytology in his biology department at the University of
Pennsylvania: “The older members of this strongly cytological department received
the Darlington book with stiff attitudes of outrage, anger, and ridicule. The book was
considered to be dangerous, in fact poisonous, for the minds of graduate students…
Those of us who had copies kept them in a drawer rather than on the tops of our
desks.”10 At the Sixth International Congress of Genetics at Ithaca in the winter of
1932, Darlington was given just five minutes to defend his views, and was shouted
down by a storm of critics. On the West Coast, the leading American cytologist, John
Belling, was working zealously on a scathing ‘Critical Review.’ A Canadian
colleague, Charles Leonard Huskins, offered to come across the Atlantic to punch
Darlington’s head off! In the relatively tranquil world of chromosomes, Darlington
had done something to make a lot of people very mad.
So what was all the raucous about?
To be sure, there were factual and experiment claims made by Darlington that fellow
cytologists challenged. In a science notorious for its intrinsic slipperiness - a “strange
and difficult kind of visual chemistry with rules only dimly perceived” as one
practitioner called it -11 little could be legitimately claimed which was not
immediately obvious to the visual sense. Darlington set down sweeping laws for
much that was not visually obvious. Yet almost all the initial reservations to
Darlington’s supporting observations of the behavior of chromosomes (principally the
number and frequency of chiasmata) were taken back one by one, as chromosomal
work in the early thirties tended to support his axiomatic claims. The initial factual
shock his book elicited within cytology ultimately gave way to acceptance, and by
1939 Sturtevant and Beadle, in their standard text An Introduction to Genetics, spoke
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of it as marking “the unification of chromosome cytology.”12
If Darlington’s microscopy was not the issue, than what was? Why was he being so
vigorously resisted?
Though not particularly quantitative himself, Darlington’s chromosome-centered
genetic system introduced too many dimensions for the mathematical population
geneticist to cope with. The gene was a one-dimensional variable. Whether or not
Wright, Haldane, and Fisher took them to be so, their paper and pencil models were
major oversimplifications. It was impossible for them to cope with all the effects of
selection when the mechanism controlling selection (chromosome behavior during
meiosis) and the unit that is being selected (the gene) are themselves both being
changed by selection. Unlike the gene in the mathematical population geneticist’s
scheme, Darlington’s chromosome-centered genetic system had no single dynamic
focus. It integrated several interacting variables: the shape of the chromosomes, their
number, the life cycles of organisms, their reproductive organisations and their
breeding
behavior
(outbreeding
or
inbreeding,
sexually
differentiated
or
hermaphrodite). All these were related in a system whose parts are mutually adapted
and adaptively connected. Years later the Harvard systematist and ornithologist Ernst
Mayr wrote to Darlington: “Your thinking simply did not fit into the atmosphere of
what I have dubbed ‘beanbag genetics.’”13
To be sure, Fisher realised that the hereditary mechanism itself could evolve
under pressure of selection. In his 1932 address to the Genetics Congress at Ithaca,
Fisher offered: “Others have considered the bearing of the theory of heredity on
evolution. I am going to consider the bearing of evolution on heredity.”14 His paper
“Evolutionary Modification of Genetic Phenomena” reversed the accepted order
manifested in Haldane’s address, entitled “Can Evolution Be Explained In Terms of
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Present Known Genetical Causes?”15 But the level at which Fisher posed the question
- the gene level - was different from Darlington’s - that of the behavior of whole
chromosomes. Fisher was unaware at Ithaca that Darlington had just published an
account arriving at the same principal conclusion of the relevance of evolution to
heredity, but when confronted by the young man with the notion of dynamic genetic
systems he “never appeared to hear.”16
Haldane was personally closer to Darlington, having acted as something of a mentor
during the time he spent at the John Innes as head of genetical research beginning in
the spring of 1927.
Haldane understood that the bell attached to Darlington’s
perspective must ring true in nature: the primary result of chromosome-centered
genetic systems is the generation, preservation and recombination of differences upon
which natural selection acts in furthering evolutionary change.17 Even if theoretical
models could not yet be constructed to describe the full implications of the
chromosome-centered genetic system for evolution in quantified terms, it was clear
that such chromosomal phenomena as inversions, recombination, polyploidy,
balanced lethals and ring-formation collectively play a more important role than
simple point mutations, even if they constitute merely shuffling of already existing
genetic materials instead of creating entirely new ones. Evolutionary-minded
geneticists had put all the focus on genes and mutations. Darlington now made it clear
that chromosome mechanics play an even more important role. Once again, Mayr
summed it up: “…no one made a greater contribution to the understanding of
recombination and its evolutionary importance than Darlington.”18
The conceptual difficulties presented by Darlington’s scheme, much the same as
the initial attempts to challenge his microscopy, fail to explain the harsh reaction
against his ideas. Adjectives like ‘dangerous’ and ‘poisonous’ in science are reserved
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for more than mere unusual theories. They usually rear their ugly head against what
the established community of researchers dub as scientific rebellions, full-on
challenges to orthodox wisdom, meaning daring confrontations that must, at all costs,
be put down, or else! What then can account for the unusual roughness with which
Darlington, the young and brash scientific upstart, was treated? What was he rebelling
against?
Method
In the winter of 1932, John Belling at Berkeley was engaged in preparing a
scathing attack on Recent Advances in Cytology. Belling died of heart disease at the
end of February, and in May of that year, ‘Critical Notes on Darlington’s Recent
Advances in Cytology’ appeared posthumously. “The method of the author,” Belling
wrote,
is to try to establish general propositions, and then to deduce from these.
Unfortunately, to a general proposition there are sometimes enough
exceptions to invalidate it… Darlington’s book contains too many
conjectures.19
Referring to Darlington’s writing as ‘propaganda,’ America’s leading cytologist
suggested that Darlington cut out nine tenths of his conjectures in the second edition.
Propaganda?!
Darlington was unshaken. It seemed apparent to him that the distinction between fact
and theory (especially in cytology) was useless, or only useful so long as it was
remembered that it was arbitrary. In a reply to Belling he offered a forceful
justification of his method:
Belling maintains the morphological point of view, of which he is the ablest
exponent. I maintain the analytical point of view, namely: every student
should be aware of the conjectures that may reasonably be made in regard to
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the causes of the events he is studying. I maintain it partly, perhaps, because
to me the cause is more real than the event itself.20 (emphasis added).
***
Darlington was now in America, a twenty nine year old Rockefeller Fellow for the
1932-1933 academic year, hopping between labs on the East and West coasts. On a
visit to Woods Hole (where he met Morgan and E.B. Wilson among others), a young
lady approached him after a talk and offered that they marry. Darlington knew that
such impetuousness would gravely hurt his parents, and seemed to revel in the
thought. “Promiscuity only flourished under condemnation,” he noted blithely in his
Diary. To his socially conservative parents, who wrote frantic letters in an attempt to
dissuade their rebellious son from tying the knot (“have you lost all your moral sense?
My dear boy, think a good deal of what you are doing before it is too late!… Father
has no respect left for you, and I am made to feel it. Your loving and affectionate
mother…”), Darlington chose to drive the taunt even further: “…We bathed in the son
entirely in the nude and got a little sunburned,” he wrote, no doubt relishing the
moment. Finally, miffed, he barked: “I wonder whether you will ever learn not to
expect your son to behave the same way as your next door neighbor’s sons!”.21 The
marriage (surprise, surprise!) lasted only a few months, but Darlington had already set
himself on his course. He was self-consciously fashioning himself a rebel on all
fronts. “Those who obey a general moral code,” he told his Diary, “will always resent
those who adopt an independent and changeable one… Vox populi is always vox
diaboli.”22
What was true for the bedroom, was true for the preparation slide. When Belling
attacked Darlington, he was representing an entire school of inductive, cautious
cytology now under threat from a young, gun-slinging deductive upstart. Self-taught
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and arrogant, Darlington took pleasure in bucking the old-schoolers. He found they’re
patience tiring, their focus on technical problems barren, and their caution sterile. “I
always want to preach what I practice,” Darlington now wrote in his Diary, “a
dangerous course for a rebel.”
But if the icon of careful induction had been Darlington’s target, why, still, was the
reaction against him so strong? What was it about that disciplinary landscape of
biology that rendered Darlington’s methodological rebellion ‘poisonous’ to young
minds?
The Disciplinary Landscape
The history of cytology falls rather naturally into quarter-centuries, beginning with
Oscar Hertwig’s discovery of fertilisation in 1875. From then until 1900, the mitotic
apparatus, the chromosomes, gamete formation, and early embryology were all
defined and recognised. It was an exciting period, the atmosphere charged with the
conviction that science was on the verge of uncovering the secrets of the life
processes and perhaps life itself. It was clear that cytology represented an independent
field of research at the forefront of progress in biology.
When Mendel’s laws were re-discovered at the turn of the century, cytology and
genetics stood on almost equal footing as far as the new study of heredity was
concerned. The Sutton-Boveri hypothesis of 1902 showed that chromosomes in the
nucleus of cells and traits expressed in the bodies of organisms were two sides of the
same coin, and cytology and genetics were the two handmaidens leading biology
towards the unlocking of the secrets of heredity. Before long, a close co-operation
between cytologists and geneticists gave birth to the chromosomal theory of heredity.
And yet Janssens’ chiasmatype theory of 1909 marked the beginning of a trend that
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was to re-define the role of cytology for the generation ahead. For when Morgan took
up the notion that the observed chiasmata were in fact the locus of genetic crossing
over, the statistically based breeding and mapping work of the geneticists suddenly
became emancipated. As a divide between describers and experimenters increasingly
bifurcated biology, willy-nilly cytology came to play the secondary role of supporter.
Soon, cytologists’ virtue came to lay in their utter reliability. Proceeding with extreme
caution, they would no longer make claims unless they could be verified by
increasingly stricter standards of empirical proof. This environment quickly
engendered theoretical sterility fostered by an acceptance of Bateson’s exhortation to
‘treasure your exceptions,’ and these soon amounted to hundreds of papers littered
about the cytological literature.
A comparison of E. B. Wilson’s First and Third editions of The Cell proves the point.
Wilson’s 1896 book was a highly speculative, and bold account of cytological
knowledge on the eve of Mendel’s re-discovery. Twenty-nine years later, however,
any sign of speculation had vanished without a trace, and the initial 371-page
deductive treatise had been replaced by a 1,232 page inductive collection of
disintegrated observation. Wilson’s Third Edition, replete with its hedging and
prevarications on the laws of pairing and crossing over, was precisely what Weismann
had been speaking of forty years earlier when he described the immense number of
detailed facts accumulated, for which “the intellectual bond which should have bound
them together was wanting.” From a pioneer, the cytologist had become a doubting
Thomas, and, in contrast to the budding geneticist, seemed to be doing little to help
the cause along.
Arriving on the scene just shortly after the appearance of Wilson’s book in 1925
Darlington immediately recognised his own situation reflected in that of his hero
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Weismann. Remembering Darwin’s own exhortation – “I can have no doubt that
speculative men, with a curb on make far the best observers”23 -Darlington, like
Weismann before him, felt that in an age of empiricism it was important that someone
have the courage to speculate. Darlington’s disposition, like Weismann’s, was
theoretical, despite working in a highly detailed, descriptive field. Like Weismann,
Darlington was not afraid to advance conjectures unsupported by observation, but
rather deduced from genetic assumptions. Finally, like him, Darlington was really
using cytology as a tool with which to probe the problems of greatest interest to him those of evolution. The referrentiality was intentional: Almost every Darlington paper
after 1931 quoted Weismann’s great speculation of reduction division made in 1887,
implicitly drawing the connection to his own (Darlington’s) bold speculations. When
Darlington grasped that cytology needed to be emancipated and made relevant once
more, he turned from a mere rebel with a field to a rebel with a cause; Recent
Advances in Cytology was his manifesto. Haldane gave expression to this rebellious
revolution, calling his young colleague’s research “the beginning of a new epoch, the
transition from an essentially descriptive to a largely deductive science.”24
Old school cytologists like Belling were not nearly as pleased. To them, Darlington’s
new type of bold, deductive, and often conjectural hypothesis-making represented a
threat to their scientific autonomy and credentials. Cytology after all, had come to be
defined by its cautious, meticulous, ‘show-me’ style. Anything else was plain and
simple not cytology, it wasn’t even science! If caution were thrown to the wind, and
faltered, what honor would remain in the profession? How would cytologists ever
again be trusted?
By breaking the hold of the old inductive method, Darlington shifted cytology in the
biological landscape of his day in relation to genetics and evolutionary theory.
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Cytologists could once again ask big questions about the origin of species and the
evolution of taxonomical lines, rather then slinking deeper and deeper into the
increasingly technical and unintelligible language of ‘karyokinesis’, ‘heterotypic’, and
the ins and outs of ‘Acidic-Lacmoid Squash’ methods. And where cytology could
once again dare, as in the days of Weismann, biology was sure to gain.
Nowhere was this more apparent than in what became known as ‘the evolutionary
synthesis.’ The great catalyst of this enterprise was the Russian-born American
geneticist Theodosius Dobzhansky’s 1937 book Genetics and the Origin of Species,
the first coherent work to link the ‘dry’ theories of the mathematical geneticists to
natural populations in the wild. In a series of experiments charting seasonal and yearly
morphological and genetic changes in the chromosomes of natural populations of
Drosophila (inversions, recombinations), Dobzhansky had shown how cytological
changes could be selected and influence the evolution of a population. Dobzhansky
relied heavily on Darlington’s work, citing him more than any other researcher beside
Sturtevant and Sewall Wright. Never mind that Darlington would be afforded little
credit for his role in the synthesis.25 What counted was that Dobzhansky’s book was
immensely successful in placing the chromosome at the heart of evolution.26 This had
been Darlington’s aim all along, but he was a cytologist. What business did he have
tackling evolution?! Only after Dobzhansky made it legitimate to consider
chromosome behavior in relation to evolution could Darlington’s original ideas be
slowly understood and incorporated into the mainstream. Cytogenetics, the science
Darlington in no small measure helped resurrect in the 1930s, had ultimately become,
through Dobzhansky, an important catalyst of the evolutionary synthesis, arguably the
greatest intellectual achievement in biology since Darwin. By blazing a new and
boldly deductive methodological path, Darlington succeeded in breaking down long-
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preserved boundaries between the different disciplines of the life sciences. Weismann
would have been proud.
Epilogue
Applying chromosome mechanics to evolutionary theory, Darlington had made bold
and grand speculation the very totem of his science. Method, first and foremost, was
the stuff of his rebellion. Many of Darlington’s bold speculations on chromosome
mechanics would eventually have to be revisited, even overturned.27 And while
rebellions of any kind invariably exact a price, truth, as Francis Bacon intoned, really
does sometimes emerge more readily from error than from confusion. Thus, the
general perspective on the importance of chromosome mechanics in evolution would
remain, even if it’s complex details have yet to be worked out even today.28
Darlington’s iconoclasm is important for the history of biology because it happened
just as the legacies of the two greatest biologists of the 19th century – Darwin and
Mendel – were finally being wed to each other, setting the scene for a picture of life
that has remained with us, notwithstanding a poke here and there, until this very day.
Studying Darlington’s life, one gets the feeling that nothing but unhindered
iconoclasm would satisfy this Lancashire lad’s need to justify his own existence.
When following his revolution cytology slowly returned to a more inductive, cautious
style, towards the mid forties Darlington turned to cytoplasmic inheritance, once
again exciting ire and controversy. In the fifties and sixties he turned to man, applying
the determinism he had witnessed in the dance of chromosomes under the microscope
to human history and culture, sparking even greater controversy still. “The most
important knowledge of any time is the knowledge whose truth is disputed,” he shared
with his trusted Diary. “No subject keeps my interest when I find my own view of it
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agrees with the accepted or majority view.”29 Spoken like a true rebel!
Darlington was a biologist of great intuition, but often of less than responsible
practice. He sometimes made daring claims based on little empirical evidence, even if
rooted in solid theoretical ground. Like Weismann before him, he practiced and took
pleasure in the art of the considered guess. What can we learn from his experience?
Perhaps the most important lesson is this: Science always needs both Promethean
theoretical leaps, and ant-like, blow-whistle, painstaking drudgery. At certain times,
an emphasis on the one may come at the expense of the other, but this is not always a
bad thing. In the end, the success of Darlington’s rebellion in cytology meant that a
stultified field could once again be made to thrive. That his empirics were reigned in
by the next generation of cytologists simply goes to show what Darlington himself
always believed to be true about his trade. “Science advances as though by the pulling
out of a drawer which gives on one side only to jam on the other… There is nothing to
be gained except by pulling on the other side.”30 The blind August Weismann, one of
the greatest cabinet-makers biology has ever known, would no doubt wink to that.
1
Weismann, Die Bedeutung der sexuellen Fortpflanzung für die Selektionstheorie (Jena: Gustav
Fisher, 1886), p. 295.
2
Weismann, Studies in the Theory of descent, R. Mendola trans. And ed., (New York: AMS Press,
1975), p. xv.
3
Weismann, August. 1887. “On the Significance of the Polar Globules,” Nature 36: 607-9.
4
Autobiographical notes, 14 November 1977, the Darlington Papers (DP):C.1:A.3
5
Darlington letter to his father, DP:C.5:A.169 (1922).
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6
Taped Darlington interview with Brian Harrison (25 July 19759), John Innes Horticultural Collection,
The John Innes Institute, Norwich; DP:C.88:f.82.
7
Coleman, 1970.
8
Diary, 1927, DP:g.32:A.65.
9
Darlington, 1932, p. viii.
10
Carson, in Mayr and Provine, 1998, p. 91.
11
Carson, in Mayr and Provine, p. 89.
12
Sturtevant, A.H. and Beadle, G.W., An Introduction to Genetics (Philadelphia: W.B. Saunders,
1939), p. 364.
13
Mayr letter to Darlington (13.5.1974), DP:C.104:H.160.
14
Apparently, Fisher’s aphoristic style was an improvement on what appears in print. This quote is
from Darlington, in Mayr and Provine, 1998, p. 74.
15
See Proceedings of the Sixth International Congress in Genetics, 1932 (Menasha:WI: Brooklyn
Botanic Garden, 1932), pp. 165-172, and 185-189.
16
Darlington, in Mayr and Provine, p. 79.
17
See Haldane’s preface to Darlington, 1932, p. vi.
18
Mayr and Provine, p. 23.
19
Belling, J., “Critical Notes on Darlington’s Recent Advances in Cytology,” University of Californai
Publications in Botany, 17, no. 3 (1933), quote on p. 76.
20
“Reply by C.D. Darlington,” in Belling, op. cit., p. 110.
21
Darlington letters to parents, August 1932, DP:C.6:A.184-190; Diary, DP:A.70:f.11.
22
Diary, 1930’s. not all dated, DP:g.33:A:66-70.
23
Charles Darwin letter to Charles Henry Lardner Woodd, 24 February, 1950, in F. Burkhardt and S.
Smith eds., The Correspondence of Charles Darwin, vol.4 (Cambridge: Cambridge University Press,
1985-91), pp. 317
24
Darlington, 1932, p. v.
25
Darlington was cited 14 times in Dobzhansky’s 1937 book. Moreover, Chapter 4, ‘Chromosomal
Changes,’ was 50 pages long and the centerpiece of the work. Nevertheless, Darlington is almost never
mentioned as an important player in the evolutionary synthesis literature. The exception is Mayr and
Provine, and even here Provine states in the epilogue: “The role of cytologists is especially difficult to
18
19
assess. They seem to have played no major role in the synthesis.” (1998,. p. 408). This is significant,
for elsewhere he calls Darlington’s Evolution of Genetic Systems “enormously influential” (p. 70),
meaning that his contribution is not understood as coming from cytology.
26
An immediate effect was the birth of a major branch of Drosophila work dealing with cytogenetics,
evolution, and natural populations, pioneered at Texas.
27
The universal law of pairing two-by-two ceased to be thought of as universal. Chromosomes do often
pair in threes and in fours, and evolution has found ways to safeguard orderly segregation nonetheless.
Indeed, although not yet entirely understood or explained, it became apparent that other mechanisms
besides chiasmata were playing important roles in keeping chromosomes paired in meiosis, and hence
in their orderly segregation for gamete formation.
28
While technical advances are pushing cytogenetics to greater heights (see Michael R. Speicher and
Nigel P. Carter, “The New Cytogenetics: blurring the boundaries with molecular biology,” Nature
Reviews Genetics, vol. 6, no. 10, 2005, pp. 782-792), fundamental problems such as achiasmatypy in
the male fly, the mechanism by which homologous chromosomes find each other for pairing, and a
thorough understanding of the effects of all chromosome changes on the evolution of natural
populations, remain elusive.
29
Diary entries, 1930s, not all dated, DP:g.33:A:66-70; DP:e.11:A.82 (1962)
30
Darlington, The Conflict of Science and Society (London: Watts and Co., 1949), p. 6.
Bibliography:
Coleman, William, “Bateson and the Chromosomes: Conservative Thought in
Science,” Centaurus, 15 (1970), pp. 228-314.
Darlington, Cyril Dean, Recent Advances in Cytology (London: Churchill, 1932)
Darlington, Cyril Dean, The Evolution of Genetic Systems (Cambridge: Cambridge
University Press, 1939)
Harman, Oren Solomon, The Man Who Invented the Chromosome: A Life of Cyril
Darlington (Cambridge, Mass: Harvard University Press, 2004)
Hughes, Arthur, A History of Cytology (London, Abelard-Schuman, 1959)
Mayr, Ernst and Provine, William B., eds., The Evolutionary Synthesis: Perspectives
on the Unification of Biology (Cambridge, Mass: Harvard University Press, 1998).
19