HISTORY OF BIOLOGY 1940-1953

Birth of Molecular Biology

 Antoine Danchin  & Disclaimer.

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The '40s witness the emergence of Molecular Biology. This area of biology provides the missing link between the formal nature of the gene and chemical molecules. This birth also establishes the molecular scale relevant to biology as the lower level needed for the analysis of life processes, and sets a limit to further scaling down (except perhaps in photosynthesis, in the chemical field involving electron transfers and photon capture, where quantum physics becomes relevant). During this period, the phage club played a major role in constructing the techniques and concepts of molecular biology. At this time two different approaches to understanding the nature of life prevailed. Geneticists (Delbrück, Hershey, Luria...) and some physiologists or biochemists (Avery, Chargaff, Monod...) put the emphasis on the actions observed in living processes, stressing the concept of function, while others (Astbury, Bernal, Bragg, Pauling...) stressed the role of the structure of macromolecules, trying to unravel their chemical sequences and to reconstruct their three-dimensional architecture. Some relevant aspects of the conceptual foundations that led to the emergence of molecular biology have been described in my book L'Œuf et la Poule (translated in French, Portuguese and Japanese, but not English).

1940 Pauling and Delbrück publish an article, The nature of the intermolecular forces operative in biological processes, in which they reveal the role of non-covalent bonds in macromolecules (electrostatic interactions, hydrogen bonds, van der Waals attraction and repulsion, etc.). Pauling further tries to understand the interaction between antigens and antibodies in terms of weak interactions, stressing the importance of complementarity. They comment on the work of Jordan (Hanover, 1902 - 1980), one of the founders of quantum dynamics, in which he proposed that complementarity is a fundamental property of all natural phenomena. Pauling suggests, in support of the immunochemical template theory, that the specificity of an antibody is the result of complementarity between its structure and part of the surface of the homologous antigen.  However, ignoring the selective principles at work in biological processes, he suggests that this complementarity is induced by the antigen in the variable folding patterns and non-covalent bonds of the antibody after protein synthesis has already taken place.

1940 Also in the domain of immunology, Landsteiner and Alexander Solomon Wiener (1907 - 1976) discover the Rhesus (Rh) blood factor.

1940 Ernst (Ernesto) Gustav Gotthelf Marcus (Berlin, Deutschland, 1893 - São Paulo, Brasil, 1968) publishes the Bryozoan volume of Danmarks Fauna. Initially an assistant of Karl Heider in Berlin, he was dismissed in 1935 after the death of Hindenburg, who had protected those Jews who had been awarded the First Class Iron Cross during World-War I. In 1936, he was appointed as professor at the New University of São Paulo where he worked with his wife Eveline Marcus (1901 - 1990) on Bryozoa.

1940 Following the work of Dubos, the pathologist Howard Walter Florey (Adelaide, Australia, 1898 - 1968) and the biochemist Ernest Boris Chain (Berlin, 1906 – 1979) who initially worked together on lysozyme, produce an extract of penicillin, and purify the molecule, further demonstrating the therapeutic effect of the first powerful antibiotic. They isolate the antibiotic from Fleming’s mold cultures and demonstrate that it can cure infections in animals. With Edward Penley Abraham (1913 - 1999), Chain further describes an enzyme from bacteria able to destroy penicillin: this discovery paved the way to the observation that resistance to antibiotics was to become soon a matter of concern.

1940 Ethel Brown Harvey (1885 - 1965) places unfertilized sea urchin eggs in a sucrose solution with the same osmolarity as the egg cytoplasm. The eggs are separated into two types by centrifugation. The lighter half contained the nucleus, while the heavier half was enucleated. Following the procedure for successful parthenogenetic cleavage, Harvey then activated the enucleated halves by placing them in hypotonic seawater. These activated enucleated halves ("parthenogenetic merogones") cleaved, formed abnormal blastulae (lacking a blastocoel), and hatched (under abnormal forms). This showed that the initial stages of the egg development were present in the cytoplasm, paving the way for the concept of the presence of a "message" outside the nucleus.

1940 Norbert Wiener (1894 - Stockholm, Sweden, 1964), an excellent mathematician and a polymath (he spent the academic year 1935-1936 in China as a visiting professor at Tsing Hua University in Beijing (then Peking), which gave him the opportunity to learn Putonghua, Mandarin Chinese) proposed building vacuum tube electronic computers that would perform fully pre-programmed digital calculations using binary mathematics on magnetic tape):  "In the summer of 1940, I turned a large part of my attention to the development of computing machines for the solution of partial differential equations."

1940 Helmut Ruska (1908 - 1973) (Ernst Ruska's brother) publishes the first pictures of a virus uses an electron microscope Die Sichtbarmachung der Bakteriophagen Lyse im Ubermikroskop (Naturwissenschaaften. 28: 45-46). With Gustav-Adolf Kausche (1901 - 1960) he also publishes the first electron microscope pictures of chloroplasts.

1940 Charles Edward Smith (? - 1973) and his colleagues demonstrate the usefulness of a tuberculin-like preparation of the pathogenic fungus Coccidiodes immitis in detecting prior exposure to the fungus. This preparation allowed for the delineation of the endemic area for the fungus.

1940 Hans Gaffron (Lima, Peru, 1902 - 1979) shows that algae can utilize molecular hydrogen for photosynthesis and coins the term photoreduction to characterize that part of the photosynthetic pathway.

1940 Paul Fildes (1882 - 1971) and independently Donald Devereux Woods (1912 - 1964) propose an antimetabolite theory to explain the action of antibacterial chemicals, and that the similarity in structure of para-aminobenzoate with the active group of sulfanilamide is responsible for its antibacterial action, interfering with the synthesis of folic acid.

1940 Selman Abraham Waksman (Priluka, Russia, 1888 - 1973) and H Boyd Woodruff (1917 - 2017), soil microbiologists, stimulated by the discovery made the year before by René Dubos of bactericidal substances in soil, focus their work on the medical uses of antibacterial soil microbes and discover actinomycin, the first antibacterial obtained pure from an actinomycete, leading to the discovery of many other antimicrobial products from that group of microorganisms.

1940-1941 Torbjörn Oskar Caspersson (1910 - 1997) shows that cell growth is associated to RNA synthesis.

1940-1943 Albert Claude (Longlier, Belgique, 1899 - 1983) isolates a mitochondrial fraction from liver by differential centrifugation.

1941 Barry Commoner (1917 - 2012) and Thimann, using auxin, find that early oat plant growth in sucrose and auxin solutions is inhibited by various substances which are known to act as dehydrogenase inhibitors. Potassium iodoacetate can halt growth but produces no effect on cellular respiration. The conclusion is that growth and respiration are not tightly linked together.

1941 Carl and Gerty Cori work out the lactic acid metabolic cycle.

1941 Publication of Charles Manning Child (Ypsilanti, Michigan, 1869 - 1954) Patterns and Problems of  Development, an analysis of development and regeneration from the viewpoint of the gradient concept.

1941 Haldane speculates that the self-controlled reproduction of a gene could be demonstrated by labelling the gene and then seeing if the copy gene contained the label while the original did not .

1941 Frank McFarlane Burnet (Traralgon, Victoria, Australia, 1899 - 1985) and his colleagues propose in The production of antibodies that the progeny of antigen reacting cells produce antibodies specific to the antigen, thus reviving ideas of Metchnikoff, focused on two experimental facts incompatible with Pauling's template hypothesis: "the continued production of antibody in the absence of antigen, and the presence of the secondary response, in which a second inoculation with an antigen elicits a host response qualitatively more rapid than that which followed the first inoculation."

1941 Åke Gustaffsson (1908 - 1988) and coworkers produce new strains of cereals with better agricultural traits by selection from mutants produced by X-rays, a practice that was to become a key player in the generation of new edible plants.

1941 William T Astbury (1898 - 1961) establishes that DNA has a semi-crystalline structure.

1941 Beadle and Edward Lawrie Tatum (Boulder, Colorado, 1909 - 1975) publish an article on their experiments using the fungus Neurospora crassa to establish that certain genes are expressed through the action of correspondingly specific enzymes; i.e., a gene controls the synthesis of an enzyme so that a mutation in a gene changes the enzymes available, thereby blocking a metabolic step. The first gene to be identified controlled the synthesis of an enzyme in a series that led to production of nicotinamide. This report is the genesis of the "one gene-one enzyme" concept. A major advantage of Neurospora over Paramecium, which had previously been used to study microorganisms, is that the former can be grown on defined synthetic media, e.g., manufactured vitamins and amino acids, whereas the latter must have bacteria as food source.

1941 At the request of Howard Florey, the young doctor Charles Fletcher (1911 - 1995) injects penicillin to a police officer, Albert Alexander, suffering with a lethal infection. Because they lacked enough penicillin (the team had even to recover some from the urine of the patient) the patient eventually died, after a dramatic improvement of his condition, providing the first demonstration that penicillin is non-toxic to humans.

1941 David Ezra Green (Brooklyn, NY, 1910 - 1983) in the first volume of Advances in Enzymology states "The thesis which we shall develop in this article is that any substance which occurs in traces in the cell and which is necessary in traces in the diet or medium must be an essential part of some enzyme. We shall define a trace concentration as one where the uppermost limit is less than 5 micrograms per gram dry weight of the cell." a thesis that had a considerable impact on the identification of coenzymes and prosthetic groups.

1941 George K Hirst (1909 - 1994) reports that when allantoic fluid from eggs infected with influenza virus  is mixed with red blood cells in ice, the cells become very heavily agglutinated. When these agglutinated cells are warmed to 37°C they disperse and can no longer be re-agglutinated in the cold by fresh virus. Hirst took this to mean that the virus has an enzyme which destroys binding sites for the virus on the red cell. Since the cell attachment proteins of most viruses also agglutinate red blood cells, this property provides a rapid, accurate and quantitative method of counting virus particles.

1941 The Manhattan Project (development of the atomic bomb) is organized with Robert Oppenheimer at the head of the scientists involved. As part of the project, Karl Lark-Horowitz, Seymour Benzer (New York, 1921 - 2007) and others developed germanium crystal rectifiers, the semiconductor later used in transistors. 

1941-1942 Charlotte Auerbach (Berlin, 1899 - 1994) with AJ Clark (? - ?) and John Michael Robson (1900 - 1982) discover that mustard gas, a highly toxic substance that had been used in trench warfare in 1914-1918, causes mutations in Drosophila altering its offspring in an hereditary fashion.

1941-1942 Gustave Malécot (1911 - 1998) introduces new probabilistic concepts in quantitative genetics, using Mendel's laws of inheritance (coefficients de parenté) to consider the probabilities that two genes are descended from different ancestral genes. He also studies "zygotic kinship chains", which measure the probability that a given chain of (diploid) ancestors occurred, a complete and mathematically rigorous probability theory for pedigree analysis, based on the degrees of relatedness between individuals in a pedigree and their probabilities of appearing in the pedigree.

1941-1943 Ludwik Rajchman is appointed advisor to the Bank of China. He befriends several members of Roosevelt's "brain trust". In collaboration with TV Soong, then Chinese Foreign Minister (and brother of Tchang Kaï-chek), he obtains a loan of 500 million dollars for China. He then becomes the unofficial director of the China Defence Supplies from which he resigns when Soong is pushed aside.

1941-1944 Archer John Porter Martin (London, 1910 - 2002) and Richard Laurence Millington Synge (Liverpool, 1914 - 1994) develop different modes of partition chromatography, including paper chromatography, and apply it to amino-acid analysis.

1942 With a very Lamarckian flavour, similar to that proposed by Piaget in his thesis in zoology (and later named accommodation), Waddington names canalization the capacity to respond to an external stimulus by some developmental reaction, such as the formation of an ostrich's calloses, which are under genetic control.  "Once a developmental response to an environmental stimulus has become canalized, it should not be too difficult to switch development into that track...by the internal mechanism of a genetic factor...; the same considerations which render the canalization advantageous will favor the supercession of the environmental stimulus by a genetic one.  By such a series of steps, then, it is possible that an adaptive response can be fixed without waiting for the occurrence of a mutation which...mimics the response well enough to enjoy a selective advantage."

1942  Brachet, after having devised histochemical means to follow nucleic acids in situ, shows that the non-nucleated daughters of enucleated cells survive for some time during which specific proteins were synthesized unless the cells were treated with ribonuclease.

1942 Julian Huxley publishes Evolution, The Modern Synthesis, still a reference today. This book lends its name to the modern synthesis of evolutionary studies created by Fisher, Haldane, and Wright. Its name "[gathers] under one theory – with population genetics at its core – the events in many sub-fields that had previously been explained by special theories unique to that discipline.  Such an occurrence marks scientific 'progress' in its truest sense – the replacement of special explanations carrying little power in prediction or extension with general theories, rich in implications and capable of unifying a diverse set of phenomena that had seemed unrelated."

1942 Ernst Mayr (Kempten, Deutschland, 1904 - 2005), in writing Systematics and the Origin of Species, champions allopatric speciation, whereby new species form only in physical isolation. It was not a new idea, as even Darwin had entertained the notion before settling on the opposite, sympatric view: that speciation does not require geographical separation. In his later reflection, he insisted the it was most unlikely that any gene remained selectively neutral, i.e., available for random drift, for any length of time.

1942 Waksman coins the term antibiotic (proposed as antibiote in 1889 by Vuillemin) to describe compounds produced by microorganisms which kill bacteria after John E Flynn (? - ?), the editor of Biological Abstracts asked him to suggest a term for chemical substances, including compounds and preparations that are produced by microbes and have antimicrobial properties. Waksman recalled the incident in his book The Antibiotic Era. Antibiotics are: "toutes les substances chimiques produites par des micro-organismes capables d'inhiber le développement et de détruire les bactéries et d'autres micro-organismes". The word was accepted quickly but its meaning became confused, Waksman published a comprehensive definition in 1947: "an antibiotic is a chemical substance produced by microbes that inhibits the growth of and even destroys other microbes and is active in dilute solutions".

1942 Albert H Coons (1912 - 1978), Hugh John Creech (1910 - 2003), Richard Norman Jones (Manchester, UK, 1913 - Edmonton, Canada, 2001), and Ernst Berliner (1915 - 2008) synthesize fluorescein isocyanate. They succeed in demonstrating the feasibility of putting fluorescent tags on antibodies and using them to localize foreign antigens in host tissues.They chemically bind the fluorescent group to anti-pneumococcus type III antibody and use a fluorescence microscope to locate the antibody in histologic sections. They also provided some basic data on sensitivity and specificity: Demonstration of pneumoccocal antigen in tissues by use of fluorescent antibody. J. Immunol. 45:159-170.

1942 Thomas Foxen Anderson (1911 - 1991) and Edoardo Salvatore Luria (Torino, 1912 - Lexington (Massachussetts) 1991) get excellent photographs of bacteriophages with an electron microscope, confirming earlier work by Ruska. They demonstrate that an E. coli alpha (T2) phage has a head and a tail: The identification and characterization of bacteriophages with the electron microscope. Proc. Natl. Acad. Sci. USA. 28: 127-130.

1942 Jules Freund (Budapest, Hungary, 1890 - 1960) and Katherine McDermott (? - ?) discover adjuvants, such as paraffin oil, that can boost antibody production significantly. The preparation is composed of heat killed tubercule bacilli in a water-in-oil emulsion: Sensitization to horse serum by means of adjuvants. Proceedings of the Society for Experimental Biology and Medicine 49: 548-553.

1942 Roman Jakobson (Moscow, Russia 1896 - 1982) one of the founders of the Prague Linguistic Circle in the '20s, proposes that the sounds of all human languages are composed of atomic units.This is developed in his Six Lectures on Sound and Meaning. He assumes that these features (now known as phonemes), are innately available by humans, individual languages being built on subsets of them.  modified views of these first suggestions that there is an innate structure for language and learning have been later developed by Noam Chomsky, and they can be based on the structure of learning processes.

1942 Brunó Ferenc Straub (1914 - 1996) and Szent-Györgi show that myosin is not the sole structural protein in muscle, but shared that role with actin. They discover that raising the salt concentration causes actin to polymerise into filaments. They also show that threads of myosin and actin, in the presence of magnesium and potassium ions, contract with the addition of adenosine triphosphate (ATP). They name the complex actomyosin.

1942 Turing goes to the US and write a report on the secret speech encypherment system that was being built at Bell Laboratories in New York for high-level transatlantic communication.

1942 Maxime Lamotte (1921 - 2007) departs for French Guinée, where he discovers in Mount Nimba the viviparous frog Nectophrynoides occidentalis, starting a passion for ecology.

1942 Norbert Wiener, Julian Bigelow (Nutley, NJ, 1913 - Princeton, NJ, 2003) and Arturo Rosenblueth (Chihuahua, Mexico, 1900 - Mexico City, 1970) basing their model on electrical engineering, propose that all voluntary action involve feedback, that "the processes of communication and control are based on the much more fundamental notion of message, [that] the nervous system [is an] array of feedback loops in active communication with the environment, [and that] through feedback...a mechanism could embody purpose" (Waldrop 2001:56).  This is a basis of a view of the mind-body problem based on the concept of automata. These automata, interestingly, are not purely mechanical as they have a dimension involving messages and communication.

1942 Douglas McClean (Constantinople 1896 - 1967) and Idwal Wyn Rowlands (St Asaph, Denbighshire, Wales, 1908 - 2005) discover hyaluronidase in mammalian sperm and its role in fertilization of the egg.

1942 Konrad Emil Bloch (Neisse, Silesia (Nysa, Polska) 1912 – 2000) and David Rittenberg (1906 -1970) using the isotope approach developed by the latter, discover that acetate is the precursor of cholesterol.

1943 Commoner, Seymour Fogel (1919 - 1993) and Walter H Muller (? - ?) demonstrate that the auxin indole-3-acetic acid promotes water absorption against an osmotic gradient. The effect is inhibited by iodoacetate.

1943 Severo Ochoa (Luarca, Spain, 1905 - 1993) demonstrates the 3:1 phosphorus to oxygen ratio of oxidative phosphorylation in the citric acid cycle.

1943 Pierre Denoix (Paris, France, 1912 - 1990), who had collected 35,000 cancer case files, some of which providedby the Parisian social services, the first French survey of cancer-related diseases, publishes the first Tumour-Nod -Metastasis (TNM) catalogue of cancer progression and diagnosis, which he develops at the Institut Gustave Roussy until 1952.

1943 Holtfreter demonstrates that dissociated cells from the same tissue will resynthesize that tissue when kept in contact with each other. He provides a detailed analysis of the three types of region-specific morphogenetic activity of cells in the amphibian gastrula and integrates this information into a unified view of gastrulation

1943 Joachim Hämmerling (1901 - 1980) demonstrates by a series of transplantation experiments that the cap morphology of two related species of the unicellular alga Acetabularia depends on the type of the nucleus.

1943 Luria and Delbrück, both creators of the Phage Group, provide statistical evidence that inheritance in bacteria follows Darwinian principles. This work marks the birth of bacterial genetics. They show that bacteria acquire resistance to phage through mutation, not adaptation, and that mutation is revealed by its selection: "When a pure bacterial culture is attacked by a bacterial virus, the culture will clear after a few hours due to destruction of the sensitive cells by the virus.  However, after further incubation for a few hours, or sometimes days, the culture will often become turbid again, due to the growth of a bacterial variant which is resistent to the action of the virus."  Certain mutants, such as those able to provide virus resistance, occur randomly in bacterial populations, even in the absence of the virus. More importantly, their randomness is demonstrated by the fact that, after several hours of cultivation in independent tubes they occur in small numbers in some populations and in large numbers in other cultures. The results, known as fluctuation analysis, show that resistance occurs before exposure to the phage and argue against the idea that mutations are induced as an adaptation to the presence of the virus.

1943 Nine months later Jacques Lucien Monod (Paris, France, 1910 - Cannes, 1976) and Alice Audureau (? - ?) obtain apparently random lactose positive mutations in a  background that was lactose negative, an observation they published after the end of the war.  At the time bacteria were supposed to have special genetic characteristics (they were assumed to have many mutations and Escherichia coli was named mutabile, for that reason). It was commonly believed the resistance of bacteria to antibiotics was the result of some sort of adaption induced by the antibiotic, which implied the Lamarckian view that acquired characteristics could be inherited. This was explained much later (in 2016) by the generation of adaptive mutations due to transcription in stationary phase.

1943 Sonneborn demonstrates cytoplasmic heredity (factor Kappa) in Paramecium.

1943 Robert Edward Hungate (1908 - 2004) who specializes in work on life under anaerobic conditions, describes an anaerobic cellulose digesting bacterium in cattle.

1943 Jean-Paul Sartre (Paris, 1905 - 1980) publishes L'Être et le Néant: Essai d'ontologie phénoménologique (approximate translation: Being & Nothingness: An Essay on Phenomenological Ontology) where he explores the perception of phenomena by the possibility of negation, or absence.

1943 Thomas Francis (1900 - 1969) and his student Jonas Edward Salk (1914 - 1995) develop a formalin-killed-virus vaccine against type A and type B influenza.

1943 During his stay at the MIT Radiation Laboratory, where he helped develop advanced radar systems that adapted the Norden Bomb Sight for “bombing through overcast” and made possible electronic and memory devices used in ENIAC and EDVAC computers, Britton Chance (Wilkes-Barre, Pennsylvania, 1913 - 2010) establishes the existence of an enzyme-substrate complex for horseradish peroxidase using spectrophotometry: The kinetics of the enzyme-substrate compound of peroxidase J. Biol. Chem.151: 553-577.

1943 Hofmann accidentally ingests through his fingertips some of the lysergic acid he had synthesized on April 16 and discovers its hallucinogenic properties. Three days later, Hofmann deliberately consumes 250 µg of LSD, and experiences far more intense effects. This is followed by a series of self-experiments conducted by Hofmann and his colleagues.

1943 Vladimir Prelog (Sarajevo, Bosnia, 1906 - 1998) succeeds in degrading cinchotoxine to optically active homo-meroquinene and reconstructing quinotoxine, a precursor of quinine from this degradation product.

1943 Kenneth James William Craik (1914 -1945) publishes The Nature of Explanation in which he proposes bold ideas about the structure of the mind while comparing it to what machines could do, well before a similar reflection by Turing.

1943 Warren S McCulloch (1898 - 1969) and Walter H Pitts (1923 - 1969) publish A logical calculus of the ideas immanent in nervous activity, where they publish the first example of conceptual neuronal networks. They further claim that the brain can be modelled as a network of logical operators on a Turing machine. This marks the beginning of models and theories which led to the use of computational metaphors and Boolean functions in the study of cognition as well as the flourishing field of neuronal networks.

1943-1947 Luis Federico Leloir (Paris, France, 1906 - Buenos Aires, Argentina, 1987) and Juan Mauricio Muñoz (? - ?) demonstrate fatty acid oxidation in cell-free liver systems.

1944 Oswald Theodore Avery (Halifax, Canada, 1877 - 1955), Colin Munro MacLeod (1909 - 1972) and Maclyn McCarty (1911 - 2005) show that bacterial transformation is caused by DNA. They use the observations of Griffith who had found that dead pneumococci can transform from an avirulent phenotype to a virulent phenotype the bacteria now known as Streptococcus pneumoniae. They show that the transforming principle is destroyed by pancreatic deoxyribonuclease, which hydrolyzes DNA, but is not affected by pancreatic ribonuclease or proteolytic enzymes. In other words, even though they were dead, the cells could transfer their genes as long as their DNA remained intact. This was a strong element to suggest that DNA, not protein, is the hereditary material. Yet, most scientists at the time were not convinced, owing partly to the cautious tone of the publication. Until that date, the majority thought genes were probably proteins. Nucleic acid, a repeated structure according to Levene, was some sort of skeletal material for the chromosomes. Studies on the chemical nature of the substance inducing transformation of pneumonococcal types: Induction of transformation by a deoxyribo-nucleic acid fraction isolated from pneumococcus type III. J. Exp. Med. 79: 137-157.

1944 Erwin Schrödinger (Vienna, 1887 - Vienna, 1961) publishes What is life? a book of reflection that triggered interest for biology at the molecular level for 30 years and was extremely influential in the birth of Molecular Biology. His most famous inspiration was that of the "aperiodic crystal" meant to represent the matter of heredity. Also, in line with the concern of his time he poses the problem of Biology in terms of a fight against degradation of all things.

1944 Peter Brian Medawar (Rio de Janeiro, Brazil, 1915 - 1987) reports that a second graft from the same donor undergoes accelerated rejection in rabbits. He links the observation to the immune system.

1944 Waksman and his colleagues discover streptomycin: Streptomycin, a substance exhibiting antibiotic activity against gram-positive and gram-negative bacteria. Streptomycin has the same specific antibiotic effect against gram negative microorganisms as penicillin does on gram positives. William Hugh Feldman (1892 - 1974) and Horton Corwin Hinshaw (Iowa Falls, Iowa, 1902 -1994) at the Mayo Clinic are the first to demonstrate successful treatment of guinea pigs tuberculosis with streptomycin with a suppressive effect on the development of the disease.

1944 George Gaylord Simpson (1902 - 1984) publishes Tempo and Mode in Evolution one of the few books that had to have a strong impact on modern biology. Simpson divides the phenomena of evolutionary change into to classes: those bearing on evolutionary "tempo" and those bearing on "mode." Tempo "has to do with evolutionary rates under natural conditions, the measurement and interpretation of rates, their acceleration and deceleration, the conditions of exceptionally slow or rapid evolutions"; "Mode involves the study of the way, manner, or pattern of evolution, a study in which tempo is a basic factor, but which embraces considerably more than tempo."

1944 Robert Burns Woodward (Boston, Mass, 1917 - 1979) and William von Eggers Doering (1917 - 2011) perform several steps of the chemical synthesis of quinine, isolated more than one century before by Caventou and Pelletier, using 8-hydroxyisoquinoline as starting material, building on the first isoalation of an optically active compound resolved from the racemic mixture by Pasteur. Over the next eighteen years, Woodward synthesizes, in 1951, cholesterol and cortisone, in 1954, strychnine and lysergic acid, in 1956, reserpine, in 1960, chlorophyll, and, in 1962, a tetracycline antibiotic.

1944 Howard Hathaway Aiken (Hoboken, New Jersey, 1900 - 1973) and a team of engineers from IBM display a huge programmable calculator, they name the Automatic Sequence Controlled Calculator, known as Mark I, which contains over 750,000 parts. It is 51 feet long and weighs five tons.

1944 (Janos) John (von) Neumann (Budapest, Hungary, 1903 - Washington, DC, 1957) and Oskar Morgenstern (1902 - 1976), starting with games such as poker or chess, apply their formulation of game theory to human economic behavior.  The central assumptions are that the players are able to foresee the consequences of their actions and will behave rationally, and according to some criterion of their self-interest.  As an application of their theory, von Neumann develops the model to the United States' nuclear strategy. Game theory was later applied to population studies and evolution.

1944 Friedrich August von Hayek (1899 - 1992) publishes The road to serfdom, a polemical defence of laissez-faire, arguing that no central economic planner could possibly command the myriad of local and individual information required, and and that only the unorganized price system of a free market allows "spontaneous order" to emerge from the myriad of individual plans. He claims, in contrst to Lange and the Paretians, that prices are not merely "rates of exchange between goods", but rather "a mechanism for communicating information."

1945 Ray David Owen (1915 - 2014) notices a surprising fact about non-identical cattle twins. Twins, who have therefore shared a circulatory system in utero, are unable to mount an immune response to antigens produced by the twin in adulthood. This is the first demonstration of immune tolerance.

1945 Edmund Brisco Henry Ford (1901 - 1988) publishes Butterflies a book in which he describes the biology of butterflies in the British Isles, integrating a view of population genetics, ecology and insect biology. This contrasts with the lack of development of genetics in France (despite isolated attempts of similar integration later developed for some time by Maxime Lamotte, for example).

1945 Colin MacLeod, Richard G Hodges (? - ?), Michael Heidelberger (1888 - 1991) and William G Bernhard (? - ?) show that an isolated capsular polysaccharide can immunize against Neisseria meningtidis. The vaccine is finally approved in 1977 after extensive international testing: Prevention of pneumococcal pneumonia by immunization with specific capsular polysaccharides. J. Exp. Med. 82: 445-465.

1945 Michael James Denham White (London, 1910 - 1983) writes a treaty on cytogenetics: Animal Cytology and Evolution. The book summarises, analyses and synthesises current information on animal chromosomes.

1945 Carl Cori demonstrates the effect of insulin on hexokinase. This is the first demonstration of such a regulatory effect.

1945 Lee Raymond Dice (1887 - 1977) publishes an article: Measures of the amount of ecologic association between species. Ecology, 26:297-302, presenting a coefficient for discrete events to appear together.

1945 Wright creates the Coefficient of Relationship to represent the probability that any two individuals share a given gene by virtue of being descended from a common ancestor. This can happen for three possible reasons in a given person, namely, that both, one only, and neither of his genes, at a given locus, are identical by descent, or c2+c1+c0=1.  The relationship is completely specified by any two of them, e.g., 2c2+c1.  One-half of this number, c2+1/2c1, may therefore be called the expected fraction of genes identical by descent in a relative.

1945 Keith Roberts Porter (1912 - 1997) describes the intracellular structure which was later to be named the endoplasmic reticulum.

1945 Luria and Alfred Day Hershey (1908 - 1997) show that bacteriophages mutate as do bacteria or other pathogenic organisms. They also introduce criteria for distinguishing mutations from other modifications: Mutation of bacterial viruses affecting their host range. Genetics 30: 84-99.

1945 Inspired by similar practices in Italy at the time, Walter Freeman (Philadelphia, Pennsylvania, 1895 - 1972) following the work of Moniz, introduces the idea of the "ice-pick" or transorbital lobotomy. With the activism of Freeman and cooperation of other surgeons around 18,000 lobotomies were performed in the US between 1939 and 1951.

1945 In another type of analysis of phenomena, differing from the existentialism of Sartre, Maurice Merleau-Ponty (1908 - 1961), in the Phénoménologie de la Perception, tries to reformulate the mind vs body problem of knowledge. He states that the foundations of science are indeed based on perception and reformulates the question of objectivity, trying a middle way excluding both Cartesian rationalism and behaviourism.

1945 Erwin Brand (1891 - 1953), Leo James Saidel (1916  -  2017), William H Goldwater (1922 - 2011), Beatrice Kassell (New York City, 1912 - 1977), and Francis Joseph Ryan (1916 - 1963) report the first complete amino acid analysis of a protein, beta-lactoglobulin, determined by chemical and microbiological methods. Brand suggests a system of symbols for the amino acids, designating each amino acid by the first three letters of its name.

1946 Joshua Lederberg (1925 - 2008) and Tatum discover that the bacteria Escherichia coli sometimes exchange genes. The proof is based on the generation of daughter cells able to grow in media that cannot support growth of either of the parent cells. Their experiments show that this type of gene exchange requires direct contact between bacteria (the process is named conjugation). At that time, it was believed that bacteria reproduced asexually, but from the work of Beadle and Tatum, it was known that fungi reproduced sexually, suggesting that bacteria did as well: Gene recombination in Escherichia coli. Nature. 58: 558.

1946 Willard Frank Libby (1908 - 1980) develops the natural radioactive carbon-14 dating technique, employing the known rate of decay, measured by its half-life, and relative proportion of its decay products to date archaeological artifacts.

1946 Reginald C Sprigg (1919 - 1994) discovers a rich deposit of Precambrian fossils (580 to 543 million years old), mostly fossilized imprints of what were apparently soft-bodied organisms, preserved on the undersides of slabs of quartzite and sandstone in the Ediacara Hills of South Australia.

1946 Errol Ivor White (1901 - 1985) discovers a fossil of Jamoytius kerwoodi, probably the most primitive known chordate from the Silurian of Lanarkshire (Scotland).

1946 André Boivin (Auxerre, France, 1895 - Strasbourg, 1949) and Roger Vendrely (? - ?) report transformation with "highly polymerised" DNA using the capsular polysaccharide of a strain of E. coli. In 1957, with Jacques Benoît, professor at the Collège de France, Colette and Roger Vendrely later participated in an infamous experiment suggesting that ducks could be transformed directly by DNA, as had been done with bacteria in the experiment by Avery and colleagues.

1946 Ulf von Euler (Stockholm, Sweden, 1905 - 1983) discovers a neurotransmitter, noradrenaline, in the sympathetic nervous system.

1946 André Michel Lwoff (Ainay-le-Château, France, 1902 - Paris, 1994) studies spontaneous "hereditary" changes in bacteria suggesting that their behaviour depends on the medium, in Some problems connected with spontaneous biochemical mutations in bacteria, Cold Spring Harbor Symp., 11: 139-155.

1946 Jacques Oudin (Dreux, 1908 - Paris, 1985) describes for the first time an immunochemical method for the identification of antigens in solid plates: "Méthode d'analyse immunochimique par précipitation spécifique en milieu gélifié" CR Acad Sci 222:115-116. This method was refined in 1949 by Örjan Ouchterlony (Gothenburg, Sweden, 1914 – 2004), and while it should be named after Oudin who invented it, it is often named after the latter only.

1946 Iwan Iwanovich Schmalhausen (1884-1963) publishes his book Факторы эволюции, where he proposes the view that the process of selective stabilisation accounts for the most important biological processes. A personal note here: my interest in selective theories stemmed from my awareness of his work, whose central thought was based on the idea of ‘selective stabilisation’ as the general driving force behind the evolution of species. I had discovered Schmalhausen's existence through my reading, without having access to his original work. However, as Marianne Grunberg-Manago (1921 - 2013) was regularly visited by Yuri Ovchinnikov (1934 - 1988), who was very influential in the development of biology in the Soviet Union, I managed to obtain the Russian original of his book, known in English by its translation in 1949 due to Dobzhansky Factors of Evolution: The Theory of Stabilizing Selection.

1946 von Neumann, Arthur Walter Burks (1915 - 2008) and Herman Goldstine (1914 - 2004) present the Electronic Numerical Integrator and Computer (ENIAC), where they use biological metaphors to define the concept of a software program, while showing how a computer can execute such a program, stored in a binary random access memory unit, following instructions from a central control unit: Preliminary discussion of the logical design of an electronic computing instrument.  This 'von Neumann architecture,' which draws its circuit designs in McCulloch-Pitts neural network notation with its sharp distinction between software and hardware, is the basis for almost all computers today. Interestingly the computer metaphor is now back in biology, with cells being seen as Turing / von Neumann machines (including the special property of being able to construct such machines).

1946-1950 Georges Teissier (1900- 1972) who had been appointed director of the Station biologique de Roscoff, becomes director of the new Centre National de la Recherche Scientifique (CNRS), created by Jean Perrin to develop research in France.

1947 Alexander Romanovich Luria (Kazan, Russia, 1902 - 1977) publishes his observations on aphasia in soldiers wounded at Stalingrad at the USSR Academy of Sciences. His work on a very large number of patients provides an enormous amount of data on the relationship between the structure of the brain and human performance.

1947 In a lecture on The Physical Basis of Life, Bernal revives the Darwin's old idea of the "warm little pond" in which life would have originated, and proposes that the lagoons and pools at the edge of the oceans served to concentrate the chemical building blocks needed to create life. He also raises the possibility that these chemicals were further concentrated by being absorbed by particles of clay. This idea, at the root of new theories of the origin of life, was later emphasised by Sam Granick (1909 - 1977), Hyman Hartman (1936 - ), Graham Cairns-Smith (1931 - 2016)  and others to counter the inadequate "primordial soup" idea, still popular and widespread today.

1947 Peter Wilhelm Joseph Holtz (1902 - 1970) discovers that norepinephrine (noradrenaline) just found by von Euler in the sympathetic system is a normal component of the brain (today named a neurotransmitter).

1947 John Tyler Bonner (1920 - 2019) publishes a study on a biological oddity: the slime mold, Dictyostelium discoideum, a "fungus" which can aggregate and differentiate into a kind of animal. He demonstrates that the interaction of chemical messages and receptors produces their aggregation into a complex organization, first a worm-like structure, then a group of cells that differentiate into a stem and a sporangium, releasing spores in the environment.

1947 Armin Charles Braun (Milwaukee 1911 - 1986) shows that Agrobacterium tumefaciens introduces a factor (later known as T-DNA, transforming DNA) into plant cells that permanently transforms them into a tumor, "crown gall". He finds that crown galls, unlike normal plant tissue, are able to multiply on a simple medium of salts and sugar, no longer requiring the supplements needed for normal plant growth. He proposes that the plant cells have been permanently transformed into tumor cells by some tumor-inducing factor introduced by A. tumefaciens: Thermal studies on the factors responsible for tumour initiation in crown gall. Am. J. Botany 34:234-240.

1947 Dennis Gabor (Budapest, Hungary, 1900 - 1979), working on improving the electron microscope, invents "wavefront reconstruction" later called holography (which is the Greek translation of the concept of rewriting in totality an image of an object in it entirety at another location). The method displays a three-dimensional image of an object (a hologram) by splitting a coherent beam of light so that part of it falls on a photographic plate and the rest on the object, which reflects back onto the photographic plate.  The two beams create an interference pattern of alternating light and dark on the plate. The plate can then be used to reconstruct the image in three dimensions.  "The light is where the two images both relect light back and reinforce each other, while the dark is where the images do not match" (Inventing the 20th Century: 100 Inventions That Shaped the World by Stephen Van Dulken, Andrew Phillips (Introduction) 2000).

1947 Théodore Monod (Rouen, France, 1902 - Paris, 2000) creates the magazine Cybium, specializing in ichtyology.

1947 William Thomas Astbury (1898 - 1961) summarizes his observations based on X-rays diffraction of nucleic acids where he tries to identify the position of nucleotides with respect to one another. He finds that the bases of the nucleotides must lie on each other, with a step of 3.3- 3.5 Å, with a specific arrangement: the interesiong point here is that this looks like another argument in favour of a piling of single nucleotides; in other words, it seems to be another argument against any idea that may still be current that a primary unit of the nucleic acids is a linked set of four nucleotides lying in a plane.

1947 In a work that would change the world, John Bardeen (Madison, Wisconsin, 1908 - 1991), Walter Houser Brattain (Amoy, China, 1902 - 1987) and William Schockley  (London, 1910 - 1989) at the Bell Laboratories, invent the transistor amplifier, a voltage and current amplifier that, unlike the vacuum tube it replaced, is an assembly of semiconductor materials with common physical boundaries. A semiconductor is a solid material, such as silicon, in which certain induced impurities enhance and orient its conductive properties. Schockley later became notorious for his racist views (and also for his involvement in setting up the "Nobel" sperm bank).

1947-1950 Lipmann and Kaplan isolate and characterize coenzyme A.

1948 Burnet and the virologist Frank Fenner (Ballarat, Australia, 1914 - 2010) propose that the immune system discriminates between 'self' and 'nonself'. The latter is notoriouus for having introduced the myxoma virus in Australia to control the explosion of the rabbitt population there.

1948 Anatolii Nikolaevich Svetovidov (1903 - 1985) establishes the systematics of gadid fishes (cod fish and related fishes) and analyses their ecology: Fauna of the USSR, Fishes, Vol. IX, no. 4, Gadiformes.

1948 The Centre National de la Recherche Scientifique (CNRS) organizes a colloquium entitled Unités Biologiques Douées de Continuité Génétique where several outstanding scientists (Max Delbrück, Boris Ephrussi, André Lwoff, Jacques Monod...) participate in the creation of the new trend of biology, Molecular Biology. Ephrussi postulates the existence in cells of cytoplasmic units, the mitochondria, that would be genetically autonomous. The mitochondrial genetic stock was to be discovered only twenty years later. The mathematician René Thom (1923 - 2002) was inspired by this meeting.

1948 George Emil Palade (Iasi, Moldavia, 1912 - 2008), together with George Hall Hogeboom (1913 - 1956) and Walter Carl Schneider (1884 - 1964) develops cytochemical studies on mammalian tissues, where, using sucrose gradients to refine the differential centrifugation method for cell fractionation and using it to isolate mitochondria.

1948 Edward Penley Abraham (Southampton, England, 1913 - 1999) extracts cephalosporin C from Cephalosporium acremonium, a fungus isolated from seawater near a sewage outfall in Sardinia. Cephalosporin C is an acid-stable molecule with antibacterial activity from which other cephalosporins are synthesized.  Together with the related penicillins, cephalosporins are the most frequently prescribed class of antibiotics. The toxicity and side effects of cephalosporins are similar to those of penicillins.

1948 The bryozoologist Marcel Prenant (1893 - 1983) at the Centre de Biologie marine in Roscoff, France, presents a systematic view of the "revolutionary" theory of acquired hereditary characters proposed by Lysenko, while taking the classical position of the Mendelian-Morganian genetics. A year later he is forced to declare that only "proletarian science" (that which supported Lysenko) could be correct. He refuses and is expelled from the Central Committee of the Communist Party.

1948 George David Snell (Bradford, Massachusetts, 1903 - 1996) building on experiments started by Peter Gorer (1907- 1961) in the UK, and transplanting tissues between mice, discovers a genetic factor, which they call H-2, for 'histocompatibility two' which determnes whether tissues are compatible between donor and recipient.

1948 Von Neumann shows that replication and metabolism are logically separable, and are in fact analogous processes associated with software (nucleic acid) and hardware (protein).

1948-1949 Hans Olof Brattström (1908 - 2000) and Erik Dahl (1914 - 1999) lead the Lund University Chile Expedition. In 1949 Brattström then becomes professor of zoology at the University of Bergen, Norway, where he completely rebuilds the Biological Station.

1949 Sigurd Orla-Jensen (1870 - 1949) and colleagues investigate the differences that may exist between the faecal flora of younger persons and those of old people. They conclude that it is not the undesirable flora found in the elderly that causes digestive disorders, but rather the digestive disorders that cause the undesirable intestinal flora. It took more than five decades for Metchnikoff's hypothesis of the beneficial role of the intestinal microbiome to be re-examined in experiments which, leaving the question open, tend unfortunately to confuse correlation with cause by attributing causality to specific microbes.

1949 Pierre Nicolle (1898 - 1984) summarizes our knowledge on bacteriophages and their use as a cure against dangerous bacterial infections.

1949 An epidemic of poliomyelitis in the USA revived the need to understand more about the disease. Thomas Huckle Weller (1915 - 2008), Frederick Chapman Robbins (1916 - 2003) and John Franklin Enders (1897 - 1985) succeed in cultivating the virus on human tissues.

1949-1950 The interest in microbes, especially bacteria, is multiplying the opportunities to identify strains and species that can be used for microbiological assays. Bacterial growth on plates is used to test the effectiveness of penicillin, streptomycin, neomycin, etc. and to explore the possible existence of new antibiotics. The difficulty of monitoring the presence of compounds in complex media (food and beverages) is a strong incentive for microbiological assays: the presence of amino acids (isoleucine, leucine, alanine, glutamic acid, tryptophan, cystine, tyrosine, phenylalanine, histidine and methionine ...), vitamins (vitamin B12, folic acid, riboflavin, nicotinic acid, ...) and other metabolites such as choline. Because they take at least 24 hours to produce a result, these methods will gradually go out of fashion, despite their interest.

1950 Roy Markham (1916 - 1979) and JD Smith show that ribonucleic acids extracted from yeast are made of nucleotides comprising the bases uracil, cytosine, adenine and guanine linked via ribose 3',5' phosphate bonds.

1950  Chargaff and coworkers validate the previous observation that DNA composition does not fit with Levene's hypothesis of a "tetranucleotide" composition with the DNA molecule itself is characterized by a marked lack of uniformity in the distribution of individual purines and pyrimidines .[...] T-DNA [thymus DNA], which is a complicated high polymer, is composed of tracts of polynucleotides, differing in the proportions, and therefore in the sequence, of their components.

1950 William Ross Ashby (1903 - 1972) explores the stability of randomly assembled nerve-networks and notes that there is a bias towards instability. This observation pleads for a specific architecture organisation in authentic neural networks.

1950 Death of André Honnorat (1868 - 1950) who founded in 1919 the Cité Internationale Universitaire de Paris, hosting university students from all over the world, and a vocal advisor for the fight against tuberculosis, founding the Fondation Roux at the Institut Pasteur.

1950 André Michel Lwoff (1902 - 1994), Louis Siminovitch (1920 - 2021) and Niels Ole Kjeldgaard (1926 - 2006) describe the process of induction of bacteriophages in lysogenic bacteria.

1951 Possibly due to the increase in allergic reactions to the newly discovered antibiotics, allergy becomes a highly fashionable topic and the International Association of Allergology and Clinical Immunology (IAACI) is founded. This later became the World Allergy Organization.

1951 Chargaff and his co-workers highlight the correspondence between adenine and thymine, and guanine and cytosine in salmon sperm DNA: Not only the ratio of purines to pyrimidines but also that of adenine to thymine and of guanine to cytosine equals 1. As the number of examples of such regularity increases, the question will become pertinent whether it is merely accidental or whether it is an expression of certain structural principles that are shared by many desoxypentose nucleic acids, despite far reaching differences in their individual composition and the absence of a recognizable periodicity in their nucleotide sequence. It is believed that the time has not yet come to attempt an answer.

1951 Gerard Robert Wyatt (1925 - 2019) who had noticed independently of Chargaff that there is always the same amount of adenine as thymine, and the same amount of cytosine as guanine in DNA identifies the presence of 5-methylcytosine in the DNAs of some species.

1951 McClintock expands her views on the diversity of chromosome instability processes in maize in a presentation at a Cold Spring Harbor Symposium that was not understood by the audience because of the still limited understanding of the physico-chemical process controlling heredity. She attributed some of the unexpected variations to a chromosomal breakage in which a chromosome lost one allele. It took several decades and the discovery of the structure of DNA to understand that this was due to transposable DNA elements.

1951 Fred Sanger and H Tuppy decipher the amino acid sequence in the phenylalanine chain of insulin.

1952 George W Dick (1914 - 1997), SF Kitchen (? - ?) and Alexander John Haddow (1912 - 1978) report the origins and emergence of the Zika virus, identified for the first time in a monkey in 1947 in Uganda.

1952 Turing proposes that a coupled system of reaction-diffusion reactions could explain morphogenesis in multicellular organisms. This model, based on a continuous view of natural processes is proposed one year before the chemical nature of the gene had been understood. While it explains pattern formation in chemistry, it remains controversial in biology, where alternative, discrete, explanations are often needed to account for what is observed. Furthermore the role of mechanical forces, now seen as an essential contribution is foreign to this early view.

1952 Alfred Day Hershey (1908 - 1997)  and Martha Cowles Chase (1927 - 2003) using radioactive sulfur (³⁵S) and radioactive phosphorus (³²P) show that bacteriophage T2 is made of DNA protected by proteins. This establishes in an unambiguous fashion that DNA is the genetic material that transmits heredity.

1952 Karl Maramorosch (1915 - 2016) publishes a study showing that cellulose acetate sheets are toxic to plants and fish. He shows that the toxicity is probably due to the plasticising compound that still contaminates the sheets. This is one of the first cases to suggest that the widespread use of plastics may have negative consequences.

1952 Luria discovers the phenomenon of restriction-modification that allows bacteria to discriminate their own genome from that of a foreign organism.

1953 Ernst J Eichwald (1913 - 2007) and in parallel Joan Michel Main (? - ?) and Richmond T Prehn (? - ?) highlight that after grafting foreign tissue natural immunity may develop against the graft.

1953 Rosalind Elsie Franklin (1920 - 1958) and PhD student Raymond George Gosling (1926 - 2015), developing her identification of two forms of DNA, A and B, that were depending on relative humidity, find experimental evidence using X-rays diffraction that contradicts the previous interpretation of similar data proposed by Pauling and Corey, while giving the exact dimensions of the double helix: If ten phosphorus atoms lie on one turn of a helix of radius 10 Å., the distance between neighbouring phosphorus atoms in a molecule is 7.1 Å. This corresponds to the P . . . P distance in a fully extended molecule, and therefore provides a further indication that the phosphates lie on the outside of the structural unit. Thus, our conclusions differ from those of Pauling and Corey, who proposed for the nucleic acids a helical structure in which the phosphate groups form a dense core.

1953 James Dewey Watson (1928 - ) and Francis Harry Compton Crick (1916 - 2004) using X-rays diffraction data from others and building up a model of the molecule propose that DNA is made of two antiparallel helices where purine::pyrimidine pairs (A::T or T::A and G::C or C::G) are stacked over one another. They postulate that two hydrogen bonds are used to stabilize the pairs (missing the fact that there are three hydrogen bonds in the GC pairs). Their conclusion is that this model explains how DNA is the substrate of genetic heredity: Despite these uncertainties we feel that our proposed structure for deoxyribonucleic acid may help to solve one of the fundamental biological problems—the molecular basis of the template needed for genetic replication. The hypothesis we are suggesting is that the template is the pattern of bases formed by one chain of the deoxyribonucleic acid and that the gene contains a complementary pair of such templates,

1953 Maurice Hugh Frederick Wilkins (1916 - 2004), William Etienne Seeds, (1922 - 1992), Alexander Rawson Stokes (1919 - 2003) and Herbert Rees Wilson (1929 - 2008) using X-rays diffraction establish that DNA fibers have a helical structure: The purpose of this article is to describe in a preliminary way further three-dimensional data of this kind and to suggest that proof is now available that deoxyribonucleic acid consists of two helical intertwined polynucleotide chains and to show, as a result of molecular model building, that this structure may be of the type suggested by Watson and Crick.

1953 Cosmologist George Gamow, originally Георгий Антонович Гамов (1904 - 1968) writes to Watson and Crick outlining a model for how the genetic code might work, in which proteins are synthesised directly on the DNA molecule itself. The model is published the following year, with the remarkable property that it shows that the double helix structure can accommodate twenty and only twenty cavities of different architecture, the exact number of proteinogenic amino acids.

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