Darlington, Cyril Dean

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DARLINGTON, CYRIL DEAN

(b. Chorley, England, 19 December 1903; d. Oxford, England, 26 March 1981)

cytogenetics, evolution.

Life . Darlington spent the first eight years of his life in Lancashire, where his father, William H. R. Darlington, was a schoolmaster. His mother was Ellen Frankland Darlington. On his father’s appointment as secretary to the chief chemist of Crossfields Soap Ltd., the family moved to Ealing in west London. Cyril attended Mercer’s School until the award of a Foundation Scholarship in 1917 led to his enrollment in one of London’s famous public schools, St. Paul’s. Darlington was no academic prodigy, and he hated sports. At home there was little time for fun and relaxation under the powerful influence of his puritanical father.

In 1920, intending to become a farmer in Australia, Darlington entered the South Eastern Agricultural College at Wye in Kent, where he took courses in chemistry, botany, geology, and zoology, as well as in such practical subjects as “seed testing, horsedoctoring, the analysis of milk and soil the construction of farm implements, the study of rents and wages and agricultural law,”1 Although he appreciated the applied subjects, the introduction to the sciences attracted him to research, and in 1923, the year of his graduation, he applied (unsuccessfully) for an Empire Cotton Corporation scholarship.

In 1922, while still at Wye. Darlington read the celebrated textbook of Thomas H. Morgan, Alfred H. Sturtevant Hermann J. Muller, and Calvin B. Birdges, The Mechanism of Mendelian Heredity (1915). Later he recalled how struck he had been “by the contrast between Morgan’s methods and arguments and those I heard discussed in connection with the breeding of crops and livestock.”2 At the suggestion of E. S. Salmon, he applied in 1923 to work under the geneticist William Bateson at the John Innes Horticultural Institution in Merton (referred to throughout this article as the J.I.). Despite a cool reception from the great man. Darlington persuaded Bateson to accept him as an unpaid voluntary worker for three months, extended to six months. In 1924 Bateson hired him. Darlington spent the next thirty years of his life at J.I. After five years on a meager studentship, Darlington was appointed cytologist, succeeding W. C. F. (Frank) Newton (d. 1927), who had been his mentor in cytology. In 1937 the J.I was reorganized on departmental lines, and Darlington became head of the cytology department. Two years later he was appointed director, thus succeeding to the post first held by Bateson.

Darlington was married three times. His first marriage was short-lived and never referred to. His second wife was Margaret Blanche Upcott, a volunteer worker in his laboratory, whom he married in 1939; they had two sons and three daughters. In June 1950 he married Gwendolen Ashead Harvey.

In 1953 Darlington accepted the Sherardian chair of botany at Oxford. By this time the most creative phase of his theoretical development was over. His reputation had been securely established with the reception of the epochal Recent Advances in Cytology, published in 1932. Consequently he was able to build up a research tradition in cytogenetics at the school of botany, where physiological, taxonomic, and ecological botany had hitherto been the chief interests of the staff. In this period he wrote many articles and book reviews on aspects of human genetics, and many historical and biographical studies that followed his text on the history of genetics.3 Despite a serious heart attack in 1964, Darlington’s energy and enthusiasm continued unabated. He initiated the first Oxford Chromosome Conference in 19644 and completed his magnumopus. The Evolation of Man and Society, published in 1969.

Darlington was one of the leading biologists of his time, but honors were not heaped upon him, for he was always a controversial figure—a corrosive skeptic whose attitude was antiestablishment and antiauthoritarian throughout his career. Nevertheless, Darlington’s early achievements were recognized by his election as fellow of the Royal Society in 1941, at the age of thirty-seven; five years later he received the Royal Society’s Royal Medal. He was president of the Genetical Society of Great Britain from 1943 to 1946, and in 1950 became a corresponding member of the Accademia dei Lincei and of the Danish Royal Academy of Sciences. On his retirement from Oxford in 1971, Magdalen College elected him to an honorary fellowship.

Scientific Method . Darlington was a theoretician with a deep interest in the fundamental questions of evolution, but at the same time he had a great love of garden plants and an absorbing curiosity concerning their origins. The modern chromosome theory, of which he was perhaps the chief architect, was important for him in both these contexts, and he was able to promote both fundamental and applied research in cytogenetics during his thirty years at the J. I. As a theoretician, however, he scorned pure empiricism. Unaware of the writings of his contemporary Karl R. Popper, Darlington stressed his view that hypotheses should be put forward in order to attempt to refute them.5 Long before the work of Thomas S. Kuhn, he argued for the theory-laden nature of facts in science. The distinction between fact and hypothesis, he explained, “becomes too naive when applied to the data of a new study. Every” fact “implies a hypothesis.”6 Quoting from Byron’s Don Juan—“Nothing more true than not to trust your senses and yet what are your other evidences?”—Darlington went on to attack the simplistic view that what we observe under the microscope can be characterized as either an artifact or not, “No appearance of treated material is definitely free from artifact, nor is any appearance” pure “artifact,” he declared.7 From this it followed that one could not impute “a morphological value to almost anything seen under the microscope.” Instead, the data of observation had to be compared against other such data and shown to be in harmony with the findings of genetics, so that “if we accept the chromosome theory, genetics and cytology have become one system.” Provocatively he declared:

… I attach greater importance to an inference from the comparison of a number of observations than to the direct evidence of a single observation. I prefer the hypothesis to the “fact”. An observation of fixed material I regard, not as an inescapable fact of life, but as an experiment with life from which one may draw various conclusions depending on its agreement with other similar experiments.8

The reason for Darlington’s concern with methodology is not difficult to determine. Cytology was riven with controversy; interpretations of the same material differed, but the ensuing conflict did not depend, he explained, “merely on details of observations or individual prejudices,” but on different habits of thought. The “older habit” that he castigated was taken from histology and placed the same confidence in the interpretation of microscopic structures as it placed in macroscopic structures: “Facts are facts and have to be accepted, however improbable.” Its unity rested on “a learned terminology, such as “matrix.”chromonema’….Behind this verbal screen a body of esoteric literature has developed, so well protected from understanding that the most critical observers on the outside have often been fain to dismiss the whole study as an imaginative imposture.” But this was no longer necessary. A new system of chromosome study could now be built if we discard the old myth terminology and apply working hypotheses’ founded on data derived from even available method of study…’9

Meiosis . Although the gross features of the process by which a nucleus divides into two daughter nuclei (mitosis) had been established in the nineteenth century, controversy continued over the “individuality of the chromosomes.” Theodor Boveri championed the persistence of the chromosomes as distinct structures throughout that mysterious “resting stage” between cell divisions when the nucleus takes on the appearance of a tangled skein of threads. John Bretland Farmer, the author of the term “meiosis,” and many others held that the chromosomes lost their individuality in the resting stage as a result of joining up end to end to form the “continuous spireme.” At the onset of nuclear division this thread was segmented to yield the chromosomes anew. It was agreed, however, that the doubling of the number of chromosomes to provide an equal set for each daughter cell was achieved by the longitudinal splitting of the chromosomes or of the spireme from which they were subsequently formed.

No such consensus existed over the procedure by which the chromosome number in the nuclei of the germ cells was halved. This special form of cell division (meiosis) had been called a “reduction division” by August Weismann in 1887 because, he

claimed, its function was to reduce the amount of hereditary material in each germ cell both qualitatively and quantitatively. Just how the chromosome number was halved, whether a qualitative reduction did occur, and by what means were questions that long continued in dispute. Added to these was the discovery from genetics that hereditary characters belonging to one linkage group are capable of being transferred to another. Assuming that each linkage group represents the hereditary units attached to a single chromosome, a cytological mechanism was needed whereby such block transfers could occur.

In 1909 Frans Alfons Janssens suggested that the crosslike figures of meiotic chromosomes, which he called chiasmata, resulted from the exchange of portions of neighboring threads. Like chromosomes associated in pairs, one maternal with one paternal, each chromosome split longitudinally into two chromatids. Under the strain of chromosome movements one chromatid from each chromosome broke and exchanged segments (Figure 1). Thomas Hunt Morgan saw that Janssens’ “chiasmatype” theory offered the required mechanism for block transfer of hereditary factors. Unfortunately the cytological evidence was unclear, and as late as 1925 Edmund B. Wilson considered it inadequate. Opposed to the chiasmatype theory was what Darlington dubbed the “classical theory,” championed by Clarence E. McClung, according to which a chiasma resulted from the exchange of pairing chromatids but without breakage and reunion, and therefore without exchange of segments (Figure 2). Consequently it did not account for recombination between genes belonging to different linkage groups, but cytologists were content that it preserved the individuality of the chromosomes and made the minimum number of assumptions about cytological processes, for neither the act of crossing-over nor the breakage of chromatids could be observed.

These rival groups were agreed on one point: the meiotic chromosomes normally paired side by side; they were parasynaptic. Yet other cytologists claimed that meiotic chromosomes paired end to end; they were telosynaptic. It was alleged that they were formed by the segmentation of the spireme, but neighboring segments remained attached end to end. The classic case was in the ring chromosomes of the evening primrose (Oenothera). Such a form of meiosis did not account for the genetic data and entailed the belief either that meiosis was not a uniform process throughout the animal and plant kingdoms or that all meiosis was really telosynaptic.

Although Bateson had reluctantly accepted the chromosome theory of heredity in 1922, he continued to seek evidence that would undermine the unique association of Mendelian segregation with meiosis. Darlington recalled receiving “encouragement, abundant meat and drink, but no positive direction” from Bateson, “for he had at that time lost his nerve and seemed to know that he was off the main track of enquiry”10 (a judgment that a study of Bateson’s later papers supports).

Fortunately, in 1922 Bateson had appointed to the J.I. a cytologist, Frank Newton, who became Darlington’s mentor. Newton was convinced that chromosomes that appeared to be paired end to end had begun their paired state parasynaptically. It was only the subsequent process of separation that gave the semblance of telosynapsis. All forms of meiosis were therefore fundamentally the same. His study of triploid tulips offered a crucial test of parasynapsis.

In 1926 Newton fell ill, and in 1927 he died. Darlington took over the preparation of his work for publication. The results confirmed Newton’s claims for parasynapsis. Yet Newton had remained skeptical about Janssens’ identification of genetic crossingover with chiasma formation. Here Darlington went beyond his mentor; he was cautiously optimistic.

If crossing-over was to be explained in terms of chromosome behavior, then maternal and paternal chromosomes had to pair in a parasynaptic manner. Parasynapsis was established by Newton’s study of triploid tulips and Darlington’s study of triploid hyacinths and diploid Tradescantia11, where it was clear that the ring formation of chromosomes resulted from parasynapsis. Applying his Tradescantia results to Oenothera, Darlington concluded that the chromosome rings in this genus were composed of chromosomes that had exchanged segments with nonhomologous chromosomes. Pairing was therefore by segments rather than by whole chromosomes (Figure 3)12.

The hypothesis of segmental interchange had first been advanced by John Belling, working with Jimson weed (Datura),13 and he had conjectured that it could be applied to Oenothera as well. Darlington followed this up enthusiastically. He argued that as a result of segmental interchange, any one chromosome in the ring was homologous at one end with one chromosome and at the other end with another chromosome. Pairing extended only a short distance back from the ends. Proximal portions did not synapse.

This hypothesis was promptly tested experimentally by others. Theresult was that Oenothera was brought into line with the parasynaptic interpretation of meiosis in other genera. Ralph E. Cleland later remarked upon the drastic change in the picture that followed. Previously Oenothera was thought to offer “the most outstanding example of telosynapsis…” Cleland quoted Edmund B. Wilson’s judgment of 1925:’ In the case of Oenothera… a “telosynaptic” association of the chromosomes in early diakinesis seems indubitable.“14 Wilson cited the many supporters of telosynapsis in plants, but he felt they had” lost ground in recent years.’15 During the 1930’s the claims for telosynapsis became increasingly implausible. Parasynapsis emerged as the rule in the meiosis of plants and animals, thus removing one of the barriers to a cytological theory of crossing-over.

The Evolution of Genetic Systems . Darlington’s study of nuclear division led him to the conclusion that the most important process involved was the pairing of homologous segments of either the split halves of chromosomes—chromatids—or of whole chromosomes. This conclusion was central to his theory of meiosis, which can be summarized as follows. The pairing process satisfies the attractive forces that operate during nuclear division. In mitosis, nuclear division begins after the chromosomes have split into chromatids. Pairing is therefore between chromatids. In meiosis, however, the division process is “precocious”; the chromosomes have not yet split when nuclear division begins. Pairing is therefore between homologous chromosomes instead of between chromatids.

When chromatids are formed, however, the paired chromosomes are no longer held together by attractive forces, which are now operating between sister chromatids. The chromosome pairs would fall apart were it not for the chiasmata that have formed between them. The chiasmata maintain the unity of the quadruple structure of the four chromatids into which the two homologous chromosomes have divided and ensure regular segregation of the four to the tetrad of cells produced at the end of meiosis. Theresult is equational and reductional—equational because each member of the tetrad receives the same number of chromosomes, reductional because homologous chromosomes (or homologous segments) are distributed to different members of the tetrad. Because the chromosomes have split into chromatids only once, yet four cells have been formed, meiosis has effected a reduction of the chromosome complement, so that the germ cells contain half the number of chromosomes found in all other cells of the organism.

Darlington was not slow to explore the biological implications of this conception of meiosis. In the summer of 1930, encouraged by J. B. S. Haldane, he sent to Biological Reviews a systematic treatment of the subject the aim of which was to establish that a uniformity of principle underlay the external diversity of meiosis. He distinguished three theories of meiosis: one morphological, one cytological, and one genetic. His precocity theory was a cytological theory. He suggested that meiosis arose as a selfperpetuating aberration of mitosis, and as the only such aberration it must be the oldest observable mechanism after mitosis. It has “made possible the recurrence of fertilisation. It has inaugurated sexual reproduction as a self-repeating process or habit.”16 Janssens’ theory of breakage and exchange of chromatid segments was the only genetic theory of meiosis, since it alone accounted for the genetic data from diploids and polyploids.

Darlington’s suggestion about the evolution of meiosis from mitosis was one of his many speculations concerning the evolution of genetic systems. This subject formed the last chapter of his Recent Advances in Cytology [afterward cited as Recent Advances], and subsequently of a whole book, The Evolution of Genetic Systems (1939). His aim was “to consider the organic world from a new point of view, the point of view not of the organism itself but of its hereditary materials and mechanism.” These two points of view differed profoundly, both at the level of analysis and with respect to their mutual relations. At the level of the genetic system there existed a remarkable uniformity in the constitution and organization of the genes, which had led to “parallelism in groups as widely separated as insects and flowering plants.” Genotypic systematics therefore transcends phenotypic classifications. Changes believed “to have occurred at re mote, chiefly pre-Cambrian periods,” he claimed, can still be inferred “from current studies of the behaviour of the genetic material in hybridization.” Theresulting inferences were often “less speculative than those drawn from the comparative morphology of the phenotype.” As for the claims of mysterious internal tendencies for different forms to evolve in similar ways—Gustav Eimer’s orthogenesis and Lev Berg’s nomogenesis—an adequate explanation was provided by the nature and “balance” of the gene and the role of the environment in eliminating less adaptive gene combinations.17

The last chapter of Recent Advances presents a vista of evolution beginning with the “naked gene”— some primitive bacteria may indeed be “single-gene organisms.”18 Mutation, aggregation, and physical association have led to the formation of chromosomes; mitosis, to their ordered replication; and meiosis, to sexual reproduction and sexual differentiation. The genetically determined suppression of meiosis has led to polyploidy, a trick by which hybrids can escape sterility. Other causes of the failure of fertilization could be overcome by apospory, apogamy, and parthenogenesis. Darlington described mutations and structural and numerical changes in the chromosomes as primary and secondary sources of variation, respectively. He judged numerical changes (polyploidy) to be more important as immediate agents of variation because they involved tested materials (that is, genotypes of proven merit), whereas mutations changed the genes, and such changes were usually disadvantageous. Numerical changes, however, depended upon the frequency of hybridization.19

Further, Darlington argued that heredity could follow two tracks. On one track the genes were separated to different chromosomes and recombined on the same chromosome by the formation of chiasmata. On the other track, genes once brought together on the same chromosome were not separated again because chiasma formation was genetically suppressed, as in the Y chromosome of Drosophila. The frequency of separation of autosomal genes was also reduced, he suggested, by suppression of chiasma formation in all chromosomes of one of the sexes—the male Drosophila, for instance. (This suggestion may have played a part in the development of the concept of a “supergene,” in which a cluster of genes was preserved indefinitely.)

The Impact of Recent Advances in Cytology . Darlington’s conclusions in Recent Advances in Cytology came under vigorous attack at the Sixth International Congress of Genetics (1932) and at the Sixth International Botanical Congress (1935), when, according to Darlington, C. L. Huskins “spoke publicly against me in all meetings and privately offered to come across the Atlantic and punch my head if ever I wrote any more footnotes about him.”20 Reviewing Recent Advances for Nature, Sturtevant wrote admiringly of the “logical and detailed marshalling of an almost overwhelming body of evidence….” Of Darlington’s precocity theory Sturtevant confessed, “[It] has an attractive logical simplicity that makes it difficult to think of the phenomena in any other terms.” However, he dissented from the theory that considered the segmental exchange of chromatids as the cause of chiasma formation. How was it that male fruit flies showed no chiasmata, yet the chromosomes remained in pairs after division into chromatids? Sturtevant also sounded a note of displeasure at the speculative character of much of the text. “There are many,” he concluded, “who will hope that we are not to see a revival of the fashion of constructing elaborate hypothetical histories that must for ever remain hypothetical.”21 At the University of Pennsylvania, Hampton L. Carson recalled, the older cytologists

… received the Darlington book [Recent Advances] with stiff attitudes of outrage, anger, and ridicule. The book was considered to be dangerous, in fact poisonous, for the minds of graduate students. It was made clear to us that only after we had become seasoned veterans could we hope to succeed in separating the good (if there was any) from the bad in Darlington. Those of us who had copies kept them in a drawer rather than on the tops of our desks.22

Darlington wrote for the expert rather than for the university student. His style in books like Recent Advances is precise but dense. Few concessions are made to the uninitiated, with the result that students were directed to Theodosius Dobzhansky, Michael J. D. White, and, more recently, H. L. K. Whitehouse in order to master cytogenetics without tears.23 The clearest account of the complex cytogenetics of the genus Oenothera was supplied by Cleland.24 Despite his renown, Darlington did not have as great an impact on evolutionary thinking as Dobzhansky, Ernst Mayr, or Ronald A. Fisher. Musing on this lack of impact, he identified two features of his conception of evolution that he thought responsible. First, “like some concepts in physics it reversed the common sense priorities of the observer,” for the organism had become the vehicle for propagating the chromosomes, and the “genetic system had become more important than the body of the individual.” Second, the genetic system “was obscure and for the mathematician it was unmanageable.” In contrast with

… the gene pool or the genetic code which vary in two or three dimensions and can be treated deductively, the genetic system operates in many dimensions. It integrates several interacting incommensurables. It has no single dynamic focus. It depends on a complex of individuals, populations and generalisations which all interact at the same time as they are being subjected to mutation, selection and recombination.25

The tidy models of the population geneticists were too simplistic for Darlington. Once or twice he tried to suggest to Fisher “that the principles of selection were not in fact going to operate with the absolute rigour he expected, but I could never get him to discuss it.”26 When Richard Dawkins “The Selfish Gene (Oxford, 1976) appeared, Darlington condemned it as a fantasy; he scorned Dawkins” predilection for models predicting animal behavior based on entirely selfish genes, a concept that Darlington saw as diametrically opposed to his own conception of interaction and feedback at all levels and between all levels of the genetic hierarchy.27

Pioneer and Controversialist . Darlington’s description of his scientific biography was always amusing, often dramatic, sometimes melodramatic, and occasionally almost paranoid. As a theoretician he was bound to encounter opposition from empirically preoccupied scientists distrustful of speculation. As a hereditarian his views on the implications of genetics for man and society did not strike a sympathetic chord in a political climate that was becoming increasingly egalitarian and antieugenic. The continuity he saw between the evolution of genetic systems and the evolution of man and society yielded a historical unity in which the hereditary material was the prime determinant of events. A gene might succeed or fail in a given environment, but it might also change that environment by action of the organism upon it. Such extreme material determinism was, and has remained, anathema to many.

Darlington’s debut in 1953 as an Oxford professor was stormy, but he succeeded in dragging the Oxford botany curriculum into the twentieth century. He established what is probably the first genetic garden in the world. Through his initiative Oxford University bought the magnificent arboretum at Nuneham Courteney. However, it was John W. S. Pringle, professor of zoology at Oxford, who was chiefly responsible for the unification of core teaching in botany and zoology, for the establishment of the chair of genetics, and for the introduction of the human sciences degree scheme.

NOTES

1. C. D. Darlington, “Biographical Notes, Articles, and Cvs Compiled by Darlington.” in Catalogue of Papers, A4.

2.ibid.,

3. C. D. Darlington. The Facts of Life (London. 1953); two valuable texts on cytogenetics are his Chromosome Atlas of Flowering Plants (London, 1956). written with A. P. Wylie; and Chromosome Botany (London, 1956).

4.Chromosomes Today, 1 (1966)—the entire issue is the proceedings of the conference.

5. See, for example, his “Meiosis in Diploid and Tetraploid Primula sinensis,” in Journal of Genetics, 24 (1931), 64–96, esp. 89.

6. C. D. Darlington, Recent Advances in Cytology (London, 1932), viii (referred to hereafter as Recent Advances).

7.Ibid., 488.

8. C. D. Darlington, “The Old Terminology and the New Anal ysis of Chromosome Behaviour,” in Annals of Botany, 49 (1935), 579–586, see 579.

9.ibid., 584–585.

10. C. D. Darlington, Royal Society personal record, 21 November 1941 (copy in Darlington, Papers A4).

11. These three papers were published in the Journal of Genetics, 21 (1929); “Meiosis in Polyploids I. Triploid and Pentaploid Tulips,” 1–16, written with W. C. F. Newton; “Meiosis in Polyploids. II. Aneuploid Hyacinths,” 17–56; and “Chromosome Behaviour and Structural Hybridity in the Trades cantiae.” 207–286.

12. C. D. Darlington, “Ring-Formation in Oenothera and Other Genera,” in Journal of Genetics, 20 (1929), 345–363.

13. John Belling and A. F. Blakeslee, “On the Attachment of Non-homologous Chromosomes at the Reduction Division in Certain 25-Chromosome Daturas,” in Proceedings of the National Academy of Sciences, 12 (1926), 7–11.

14. Edmund B. Wilson. The Cell in Development and Heredity, 3rd ed. (New York, 1925), 565; Ralph E. Cleland, Oenothera: Cytogenetics and Evolution (London and New York, 1972), 54.

15. Wilson, The Cell, 566 ff.

16. C. D. Darlington, “Meiosis,” in Biological Reviews, 6 (1931), 221–264.

17.Recent Advances, 448–449.

18.Ibid., 452.

19.Ibid., 478.

20. C. D. Darlington, Royal Society personal record.

21. A. H. Sturtevant, “Chromosome Mechanics,” in Nature, 131 (1933), 5–6.

22. Hampton L. Carson, “Cytogenetics and the Neo-Darwinian Synthesis.” in Ernst Mayr and William B. Provine, eds. The Evolutionary Synthesis: Perspectives on the Unification of Biology (Cambridge, Mass., 1980), 91.

23. Theodosius Dobzhansky, Genetics and the Origin of Species (New York, 1937); Michael J. D. White, Animal Cytology and Evolution (Cambridge, 1945); H. L. K. Whitehouse. Towards an Understanding of the Mechanism of Heredity (London, 1965).

24. R. E. Cleland, Oenothera.

25. C. D. Darlington, “My Approaches to Genetics and Evolution,” in Papers, A2, 10.

26. C. D. Darlington, “J. B. S. Haldane, R. A. Fisher, and William Bateson.” in Ernst Mayr and William B. Provine, eds., The Evolutionary Synthesis, 430.

27. C. D. Darlington, “In the Evolutionary Soup,” Times Literary Supplement (4 February 1977), 126.

BIBLIOGRAPHY

I. Original Works. A comprehensive biblography of Darlington’s publications is in D. Lewis’ bibliographical memoirs (see below). Darlington assembled and published his own guide to his published works in C. D. Darlington and Collaborators: bibliography 1926–1971 (Oxford, 1971). Of his thirteen books the most important is Recent Advances in Cytology (London and Philadelphia, 1932; 3rd ed. 1965). The most interesting of his pamphlets is his Conway Memorial Lecture of 20 April 1948. The Conflict of Science and Society (London, 1948). The best textbook is the one he wrote with Kenneth Mather, The Elements of Genetics (London and New York, 1949; repr. 1952). The most successful of his popular texts is the historical study The Facts of Life (London, 1953; repr. 1956); the 2nd edition is titled Genetics and Man (London, 1964; repr. 1967), Both editions have been translated into numerous languages. His Evolution of Man and Society (New York, 1969; London, 1970) has been translated into seven languages.

Darlington’s personal account of the events leading to the synthesis of Mendelism and Darwinian evolution is in “The Evolution of Genetic Systems: Contributions of Cytology to Evolutionary Theory” and “J. B. S. Haldane, R. A. Fisher, and William Bateson,” in Ernst Mayr and William B. Provine, eds. The Evolutionary Synthesis: Perspectives on the Unification of the Biology (Cambridge, Mass., 1980), 70–80, 430–432.

II. Secondary Literature. For a fine overview of Darlington’s many contributions to science and to the profession of genetics, see D. Lewis, “Cyril Dean Darlington,” in Biographical Memoirs of Fellows of the Royal Society, 29 (1983), 113–157. Also invaluable are the introduction and notes to the catalog of his papers compiled by Jeannine Alton and Peter Harper, Catalogue of Papers and Correspondence of Cyril Dean Darlinaton (1903–1981), Deposited in the Bodleian Library, Oxford (Oxford, 1985). Darlington’s study of the chemical aspects of chromosome behavior and his participation in multidisciplinary discussions of the nature of the gene are described in Robert C. Olby. The Path to the Double Helix (London and Seattle, 1974), chap. 7.

Robert C. Olby