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The term super-spreader is used for multiple, and sometimes even conflicting, purposes. The reasons for this can be traced back to its complex history. Forerunners of the super-spreader concept—in discussions of so-called dangerous carriers and in analyses of explosive outbreaks during the early 20th century—revolved primarily around gastrointestinal diseases, not respiratory ones. In 1957–58, the H2N2 influenza pandemic and Wells and Riley's studies on tuberculosis drew attention to both the viability of airborne transmission and the existence of significant heterogeneity in infectivity. The term super-spreader was coined in 1972, in relation to computer simulations of influenza epidemics. Initially, super-spreaders were simply an additional feature within stochastic models of epidemics, with little effect on an epidemic's eventual course. The term was later appropriated to explain why outbreaks of airborne diseases continued in vaccinated populations, defying the predictions of contact-transmission-based models. The content and meaning of the term continued to fluctuate, from the mathematical characterisation of sexually active people with gonorrhoea, through HIV carriers with highly infectious semen, to central nodes within a network. This Historical Review reconstructs the historical growth of the concept of super-spreading, and offers insight into its current, highly diversified use.

In discussions about super-spreaders, one figure who features prominently is \"Typhoid Mary\"-the Irish immigrant cook who was an asymptomatic carrier of typhoid bacilli, infected 47 people, and led to at least three deaths in early 20th-century New York State. In the past three years, references to Typhoid Mary, whose real name was Mary Mallon, as the first, most prominent, or prototypical example of a \"super-spreaded' are common in scientific papers, blogs, videos, podcasts, and articles in the popular press (see the Appendix, available as a supplement to the onlineversion of this article at https://ajph.org).Does the historical case of Mary Mallon really qualify her for such a role? The answer obviously depends on how we define super-spreaders. Contemporary applications of the term vary, but most commonly it is used to referto individuals who instigated an \"explosive outbreak\" of simultaneous infections, or to the theoretical discussion of infectiousness heterogeneity in shaping the course of epidemics. Super-spreading, in the sense of actual or potential \"extraordinary\" infectiousness, is described as caused by (1) biological, physiological, or immunological mechanisms or (2) as grounded in social or behavioral dynamics. At first glance, Mary falls into the latter category: she was an asymptomatic carrier of Salmonella typhi who worked as a cook and was characterized by health officials as lacking in personal hygiene. Thus, she had all necessary qualifications to unknowingly and effectively disperse pathogens. Nonetheless, I argue that her story is hardly compatible with our contemporary understanding of super-spreading and that the tendency to associate her with the term is scientifically, historically, and morally precarious.

[...]from January 1934, German citizens with mental or physical defects began to face hereditary tribunals that decided whether or not they should be sterilized. According to Muller (1950), the relaxation of natural selection in modern society would \"ultimately lead to an ever greater heaping up of mutant genes.\" The task was a daunting one because the average man \"will be inclined to give priority to his immediate concerns, the interests of which will often (at least under existing mores) run counter to those of the seemingly immaterial abstractions conjured up by the geneticist.\" [...]only, \"after the processes and consequences of genetic change throughout the ages have been vividly visualized and dramatized for people in general from their early years on through their later developments, can we expect the arguments, calculations and recommendations of geneticists to take on sufficiently concrete meaning for the average man.\" [...] genetic load gradually evolved from an inherently negative concept to a neutral one and even to include a beneficial component and aspect-indeed, a \"sine qua non for evolution,\" as had been suggested by Haldane already in 1937 (Haldane 1937; Crow 1970, p. 173).

Between 1880 and 1920 the medical quest to unearth the causes of disease saw two pathbreaking discoveries. One was the bacteriological revolution – the identification of specific germs as causal agents of specific diseases (anthrax, tuberculosis, diphtheria, cholera and so on), and the simultaneous effort to develop disinfection techniques and immunisation measures to combat these diseases. The other was the rediscovery of Mendel’s laws of heredity and the resulting emergence of medical genetics, where an entire set of medical maladies (deafness, blindness, bodily deformities, haemophilia, Huntington’s chorea, feeble-mindedness and many mental diseases) were identified – rightly or wrongly – as genetically determined. The ‘germ theory of disease’ and the ‘gene theory of disease’ shared striking, all-too-often overlooked similarities. Both theories built on shared epistemological assumptions that influenced their explanatory mechanisms and their overall conceptual frameworks; both mobilised similar visual and linguistic vocabulary; both appropriated – and enforced – prevailing cultural and gender norms; and both enshrined broadly parallel hygienic practices. Reflecting similar social concerns, medical bacteriology and medical genetics acquired kindred scientific and societal configurations, which this paper highlights and scrutinises.

The introduction of blindness into the Sterilization Law passed by the Nazis in July 1933, was exceptional, even by the standards of the time. Prior sterilization bills had focused on mental and nervous disorders, and they almost always excluded blindness as a category. The wish to sterilize the blind cannot be explained solely as stemming from the eugenic or economic threat that they allegedly posed to German society; such threats were acknowledged to be marginal, and they paled in comparison to the perceived menace attributed to the so-called feeble-minded and mentally ill. What made blindness of special significance for Nazi lawmakers was its disciplinary status among geneticists as an indisputable demonstration of the validity of the laws of heredity to human maladies. Together with two additional disease categories—deafness and Huntington's chorea—blindness provided Nazi legislators with scientific legitimization that helped pave the way for the sterilization of the mentally ill. For the blind, it was therefore not the fanaticism of the Nazis but rather their aspiration to ground their policy in biological teaching that ultimately proved fateful. Sogar gemessen an den Standards der damaligen Zeit war die Einbeziehung der Blindheit im von den Nationalsozialisten im Juli 1933 erlassenen Sterilisationsgesetz außergewöhnlich. Frühere Sterilisationsgesetze waren auf mentale und nervlich bedingte Störungen fokussiert gewesen und hatten Blindheit als Kategorie fast immer ausgeschlossen. Das Bedürfnis Blinde zu sterilisieren kann nicht einfach dadurch erklärt werden, dass diese angeblich eine eugenische oder wirtschaftliche Bedrohung für die deutsche Gesellschaft darstellten; man gab ja zu, dass derartige Bedrohungen marginal waren und in keinem Vergleich zu der durch sogenannte Schwachsinnige und psychisch Kranke empfundenen Gefahr stand. Die besondere Bedeutung der Blindheit für die nationalsozialistischen Gesetzesgeber beruhte auf deren Status innerhalb der Genetik, da man durch Blinde die Vererbungsgesetze bezüglich menschlicher Krankheiten unanfechtbar demonstrieren konnte. Zusammen mit zwei weiteren Krankheitskategorien – Taubheit und Huntingtonsche Chorea (Veitstanz)—lieferte Blindheit den NS-Gesetzgebern die wissenschaftliche Legitimation, um den Weg zur Sterilisation der psychisch Kranken zu ebnen. Den Blinden wurde daher letztendlich nicht der Fanatismus der Nationalsozialisten, sondern deren Bemühen, ihre Politik durch biologische Erkenntnisse zu rechtfertigen, zum Verhängnis.

The seventh section of Gregor Mendel's famous 1866 paper contained a peculiar mathematical model, which predicted the expected ratios between the number of constant and hybrid types, assuming self-pollination continued throughout further generations. This model was significant for Mendel's argumentation and was perceived as inseparable from his entire theory at the time. A close examination of this model reveals that it has several perplexing aspects which have not yet been systematically scrutinized. The paper analyzes those aspects, dispels some common misconceptions regarding the interpretation of the model, and re-evaluates the role of this model for Mendel himself. In light of the resulting analysis, Mendel's position between nineteenth-century hybridist tradition and twentieth-century population genetics is reassessed, and his sophisticated use of mathematics to legitimize his innovative theory is uncovered.