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producing new life has been taken as a given. ESSAY That did not mean, however, that the two sexes were considered to make complemen- Heredity before genetics: a history tary contributions, or that there was thought to be any consistent observable relation between parents and offspring. A classic Matthew Cobb assumption — which persists in much folk- Abstract | Two hundred years ago, biologists did not recognize that there was lore today — turned the apparent prehistoric focus on women on its head, producing a such a thing as ‘heredity’. By the 1830s, however, insights from medicine and male-centred view. Semen — the only imme- agriculture had indicated that something is passed from generation to diately apparent product of copulation — was generation, creating the context for the brilliant advances of Mendel and thought to be ‘seed’ (‘semen’ means seed in Darwin. Recent work on the history and philosophy of science has shed light Greek); parents still talk to children about on how seventeenth-, eighteenth- and nineteenth-century thinkers sought to ‘Daddy planting a seed in Mummy’s tummy’. understand similarities between parents and offspring. The Ancient Greeks came up with two contrasting views of human generation: Hippocrates argued that each sex produced The existence of heredity is now so firmly subject to intense philosophical and ‘semen’, which then intermingled to established that it is difficult to imagine a practical scrutiny. produce the embryo, whereas Aristotle time when we did not realize that there were Although the three strands of thought claimed that the woman provided the consistent relations between parents and that I discuss were not strictly separate, the ‘matter’, in the shape of her menstrual offspring. But, as little as two centuries ago, professionalization of science and medicine, blood, with the father’s semen providing the word ‘heredity’ had no biological mean- and the different values that were placed the ‘form’, shaping the female contribution ing. There was no study of heredity for the on different kinds of knowledge, tended to in some unknown way. The great physician simple reason that it had not been realized isolate ideas in each of these fields until Galen, whose approach was to dominate that such a phenomenon existed. For at least the 1830s, when they came together to set the European and Arab medicine for around 2,000 years, discussions of similarities and scene for the world-changing breakthroughs 1,500 years, adopted many of Hippocrates differences between offspring and parents of Mendel and Darwin2. ideas, including his ‘two-semen’ theory of were tacked on to more general explana- generation. tions of the origin of life — ‘generation’. This Earliest thoughts about life Although both the Aristotelian and term was used to describe a single, perplex- The oldest examples of human figurative art the Galen–Hippocrates views focused on the ingly complex phenomenon that we would are of the female body or genitalia, and it is mechanisms of how life was formed, they today consider to be a fusion of reproduc- generally assumed that they were in some also attempted to explain the similarities and tion, genetics and development. In dealing way associated with female fertility3. It seems differences between offspring and parents solely with the ‘heredity’ side of generation, most likely that, until the domestication of that everyone could notice. The two-semen much of this article is therefore a deliberate animals provided a simple model, humans theory naturally led to a view of generation anachronism, a focused but partial descrip- did not appreciate the link between sexual (and therefore of resemblance) that involved tion that the people whose work it describes intercourse and pregnancy, or that both the blending of the parental contributions. would not have recognized1. sexes are involved in creating life. Women Similarly, Aristotle recognized that his Over the past decade, historians and phi- alone had that power. This supposition is male-centred view needed to take account losophers of science have shed new light on supported by the widespread existence of of the role of the female, so he argued that the sources that enabled Mendel to lay the matrilineal communities in hunter–gatherer the matter (the female contribution) could foundations of genetics, and Darwin to put societies, and by modern anthropological affect the form (the male contribution), just heredity at the heart of his theory of evolu- evidence that the matrilineal Trobriand as a plant would look different if a seed was tion by natural selection. Three strands Islanders of Papua New Guinea had no grown on different soils. However, neither of knowledge — science, agricultural concept of biological fatherhood (although man put forward a description of anything practice and medicine — each provided this suggestion has been contested, it is the like ‘heredity’, because there did not seem to key insights on the road to heredity. This case that their word for ‘father’ means ‘my be any consistency in what they observed. took place in a political and social context, mother’s husband’)4. The ideas of Aristotle and Hippocrates symbolized by the French Revolution of Whatever the case, for the most recent dominated Western (including Islamic) 1789, in which the traditional meaning part of humanity’s history — that which has ideas about generation for over 1,500 years. of ‘heredity’ — a legal term relating to occurred since the rise of civilization — the On the other side of the planet, Chinese property and monarchical power — was involvement of both males and females in thinking about generation did not try to

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at the time, was not even recognized to exist: consistency in the relations between parents and offspring, or heredity. The problem was not that thinkers did not look for similarities between the generations, but that they did, and were understandably confused by what they saw. Human families provided striking, highly contradictory and apparently inconsistent evidence — children sometimes looked like one parent, sometimes a mixture of the two, sometimes like neither and sometimes like their grandparents. Harvey perceptively summed up the dif- ficulties in his 1651 work, De Generatione Animalium (‘On the Generation of Animals’) (FIG. 2). Harvey mused: “…why should the offspring at one time bear a stronger resemblance to the father, at another to the mother, and, at a third, to progenitors both maternal and paternal, farther removed?” He had no answer, but he had other ques- tions, such as why some birthmarks and moles recur from one generation to the next, whereas others do not. Finally, Harvey contrasted the pattern Figure 1 | Leeuwenhoek’s illustration of spermatozoa. Antoni Leeuwenhoek discovered sperma- that was seen for most characters, which tozoa in 1677, although the name was coined in the 1820s by Karl-Ernst von Baer. Image courtesy seemed to involve some kind of mixture of © of the author (2006) M. Cobb. the parental types, to that which is seen in the sex of individuals, which in virtually all cases shows no blending at all: “I have frequently locate functions in structures, but instead Surprisingly to the modern eye, no one wondered how it should happen that the focused on the ‘generative vitality’ of each in the seventeenth century argued that eggs offspring, mixed in so many particulars of its sex, defined in terms of the energy flows of and sperm represented complementary ele- structure or constitution, with the stamp of organ networks5. On a world scale, there ments that made equivalent contributions both parents so obviously upon it, in so was little agreement about how generation to the offspring. Instead, the next 150 years many parts, should still escape all mixture took place, about the contribution of each were dominated by either ‘ovist’ or ‘spermist’ in the organs of generation; that it should sex, or about how and why offspring visions of what eventually became known as so uniformly prove either male or female, so resembled parents. ‘reproduction’ (the term was coined only in very rarely an hermaphrodite.”8 Harvey’s 1745) (REF. 7). Each view considered that only string of apparently contradictory examples Early scientific studies of generation one of the two parental components pro- shows how difficult it was to discern any kind The first important advance in understand- vided the stuff of which new life was made, of pattern in the facts of heredity by simply ing ‘generation’ came in the second half with the other component being either food observing a range of human characters. of the seventeenth century, through the (as the spermists saw the egg), or a force that In a rare experimental study of resem- work of Reinier de Graaf, William Harvey, merely ‘awoke’ the egg (as the ovists saw the blance, Leeuwenhoek provided yet another Francesco Redi, Nicolas Steno and Jan spermatozoa). example of the way characters appeared in Swammerdam6. Using theory, dissection There were many reasons underlying this each generation, and added to the prevailing and experimentation, they provided proof apparent scientific dead end. For example, perplexity. Using what could have been a that ‘like breeds like’ in all parts of the in chickens, the two elements did not seem tractable model — rabbits — Leeuwenhoek macroscopic world (including the difficult to be equivalent at all: there was a single was surprised to find that a grey male wild case of insects, which everyone, includ- enormous egg, which was apparently pas- rabbit could give rise to only grey offspring. ing Harvey, had thought were generated sive, whereas the ‘spermatic animals’ were But Leeuwenhoek argued that spermatozoa spontaneously), and put forward the theory microscopic, incredibly active, and present were the sole source of the future animal, that all female organisms, including women, in mind-boggling numbers. Ultimately, how- so his strange finding from rabbits became produced eggs. A few years later, Antoni ever, the reason that late seventeenth-century “…a proof enabling me to maintain that the Leeuwenhoek rocked the world with his thinkers did not realize what to us seems foetus proceeds only from the male semen discovery of spermatozoa (FIG. 1) (although blindingly obvious — that both eggs and and that the female only serves to feed and they were not called this until the 1820s, by sperm make equal contributions to the future develop it.”9 In other words, there was Karl-Ernst von Baer, who was also the first offspring — was that there was no compel- no relation between both parents and person to actually observe the mammalian ling evidence to make them appreciate this. the offspring, but simply between father and egg). All the components were there, but no Worse, such evidence could (and would) offspring, which was represented by the little decisive advance was made. come only from the study of something that, animal in the male semen. The father was

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grey, so the offspring were inevitably grey, straightforward relation between parent and thought Leeuwenhoek. offspring, and undermined the great step It is tempting to imagine that if he had forward that was made by work on genera- done the reciprocal cross, using a grey female tion in the 1660s, the certainty that ‘like wild rabbit, or if he had studied the grand- breeds like’. Implicit in all this — although children of his grey male, Leeuwenhoek it was never stated at the time — was the might have paused for thought and the assumption that, were it not for varied intercourse of science might have been changed. vening factors, offspring would look just like Sadly, given Leeuwenhoek’s self-proclaimed either their father or their mother. Because stubbornness and his habit of breezily there was no discernible pattern to the way ignoring contradictory evidence6, it seems those factors affected appearance, no one much more likely that he would have either pursued the matter further. discarded his findings or found another explanation that supported his certainty that Eighteenth-century insights spermatozoa were the sole contributors to In the first part of the eighteenth century, the the future organism. question of the reappearance of characters The ovist and spermist visions of genera- across generations was implicit in the ideas tion that dominated eighteenth-century of Linneaus, through his work on plant thinking were characterized by the idea of hybridization, taxonomy and reproduction, ‘pre-formation’, whereby the future organ- and in Antoine-Nicolas Duchesne’s presenta- Figure 3 | Polydactyly. Maupertuis and Réaumur studied how polydactyly was inherited through ism was contained in either the egg or tion of a new variety of strawberry11,12, but the generations. the sperm. To explain why offspring were neither man discussed the question explic- nevertheless not identical to either parent, itly. Surprisingly, neither did Lamarck (‘the thinkers could point to Aristotle’s suggestion inheritance of acquired characteristics’ is a that plant seeds grew differently depending much later formulation of his ideas)13. that polydactyly would not be transmitted on soil conditions, although many people The most prescient eighteenth-century over three consecutive generations (the result felt uncomfortable with this explanation10. approach to hereditary phenomena came was a staggering 8 × 1012 to 1) (REF. 16). Like Similar post-hoc explanations were used from Pierre Louis Moreau de Maupertuis, his general ideas about generation, however, to explain the appearance of ‘monsters’ although it had no effect on mainstream Maupertuis’s calculation had no impact at the (offspring with striking birth defects), thinking at the time. In 1745, Maupertuis time, and there is no evidence that Mendel, which seemed to indicate that there was no used the famous case of a ‘white negro’ (a who used a statistical analysis of large data black albino child) and put forward a theory sets, knew of his approach. of both similarity and development14. For Despite such examples, which for us seem Maupertuis, both parents contributed ‘parti- extremely telling, by the early years of the cles’ to the offspring; if there were too many nineteenth century, scientific approaches or too few of one type of particle, a monster to the study of generation had not revealed could appear. Maupertuis perceptively sug- that there was such a thing as biological gested that the albino child’s colouration heredity. Indeed, thinkers still did not realize could be due to ‘particles’ from an ancestor, that both sexes contributed equally to the or to a change in the particles themselves. offspring (Réaumur and Bonnet’s discovery This theory was rejected by most of his of aphid parthenogenesis in the 1740s had contemporaries, mainly because Maupertuis not helped matters). Even the first person ignored the best evidence of the time and to see the mammalian egg, Ernst von Baer, dismissed the roles of both eggs and sperm, was a convinced ovist who, in common with adopting a version of the Greek atomist idea many other thinkers of the time, classed of ‘pangenesis’, according to which genera- spermatozoa as parasitic worms. tive particles existed in all tissues15. In some ways, the scientists who tried to A few years later, Maupertuis and study generation succeeded only in making René-Antoine Ferchault de Réaumur both the reality of biological heredity even more studied polydactyly (FIG. 3), using families difficult to discern. The multiple and con- from Germany and Malta, respectively. tradictory examples they provided, and the Decisively, both thinkers looked at the way microscopic enigmas that their instruments the character reappeared over the generations revealed, were ultimately less informative — Maupertuis had data from four genera- than the very practical knowledge that had tions, Réaumur from three. The pattern they recently been developed in agriculture. Figure 2 | The frontispiece to Harvey’s De observed was clearly not that which was Generatione Animalium. Zeus is shown on the expected by pre-formation (not all offspring New thinking from breeders cover of William Harvey’s 1651 work, in which he were affected), nor was it a one-off phenom- At the heart of agricultural practice is the outlined problems in understanding the simi- enon like a monster. Maupertuis even took assumption that, as Thomas Blundeville, larities between parents and offspring. Image a step towards a probabilistic analysis of an author with an interest in horse breeding, courtesy of the author © (2006) M. Cobb. heredity when he calculated the probability mathematics and navigation, put it

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in 1566: “…it is naturally geven to every beast animals from Arabia, the horses generally Bakewell seized on the opportunity that for the moste parte to engender hys lyke.”17 failed to flourish and rarely reproduced all was provided by the growing demand However, as Blundeville indicated, this the qualities that had made them attractive for mutton in a thriving UK economy, to was not always the case, and until the in the first place. As a result of many such launch a deliberate programme of selective seventeenth-century studies on generation, it experiences, “…most authors believed that breeding to create a race of sheep that grew was not even clear that it applied to all organ- the virtue of horses from exotic locations was more quickly and produced more meat than isms. More surprisingly, until the second half only transmissible over generations while traditional breeds. of the eighteenth century, there does not seem they remained in these places.”18 Far from Bakewell’s procedure was painstaking and to have been any explicit attempt to exploit seeing the characters of their animals as involved scouring the surrounding counties this phenomenon; selective breeding, in having an innate, constitutional basis that for animals that met some or all of his four terms of a conscious decision to manipulate could pass from one generation to another, criteria: ‘beauty’, the proportion of edible to the stock of a domesticated organism, was breeders — like Aristotle and other thinkers non-edible parts, meat quality and growth not widespread, nor was it transformed into — accepted that local conditions had a rate. The key point was that male and female a theory. Breeders’ ‘knowledge’ that like bred decisive role in shaping characters. had to be matched, and that the focus was like was partial and entirely heuristic: they From the seventeenth-century, breeders on the development of a herd of animals were concerned with what worked, not why18. tended to use the term ‘blood’ to describe with similar characteristics, rather than on Partial insights that seem striking to us the quality that apparently lay behind the producing occasional outstanding individu- were not exploited or used as the starting characters of an animal. But, as with a royal als. This required Bakewell to think in terms point for further knowledge. For example, ‘bloodline’, this was a vague, semi-mystical of populations — one of the keys to realizing in the second half of the first century, Lucius view of the power of an imprecise quality, that there is such a thing as heredity. Junius Moderatus Columella summarized rather than a recognition of the hereditary The aim of Bakewell’s work, which was Roman agricultural knowledge in De Re transmission of characters. This confusion pragmatic and heuristic in approach, Rustica (‘On Rural Matters’). Problems that was translated into practice: eighteenth- was simple: he frankly described his barrel- were associated with animal breeding take century racehorse breeders would not shaped breed, the New Leicester (FIG. 4), as up only a few sentences, although Columella cross two successful racehorses, creating “…a machine for turning herbage … into noted that blending of coat colour was typi- a ‘thoroughbred’ stock, but would instead money.”20 He claimed that castrated New cally the case, and the grandsire’s coat colour cross racing stallions with local mares18. Leicester rams could be killed for best profit could reappear in the second generation19. During the eighteenth century, however, at two years, rather than the four years that However, this was not enough to spark his or agricultural breeders in the United Kingdom was typical of other breeds — an increase in anyone else’s interest. — in particular, sheep breeders — began productivity that indicates the effectiveness The difficulty with the breeders’ basic to appreciate the power of selection, and to of his breeding programme. assumption that like breeds like was that create new, true-breeding lines of animals20. The financial impact of Bakewell’s work it was not always true. As Nicholas Russell The key figure was Robert Bakewell, a sheep was substantial, and he was able to hire out has pointed out, when seventeenth-century breeder from Dishley, near Loughborough, his rams for over £1,000 for a season (an English horse breeders tried to import England. In the middle of the century, astonishing sum at the time), but the huge cost of maintaining his rigorous selection programme meant that he was perpetually in danger of going into debt (he nearly went bankrupt in 1776). Because of the potential for making large sums of money, visitors came from all over Europe to study Bakewell’s amazing man-made sheep, and his equally astonishing breeds of horses, pigs and cattle. Farmers from France, Germany, Russia and Austria all sought to copy his techniques. The scientific community was less impressed. The president of the Royal Society, Sir Joseph Banks, was not only a leading botanist, but also a major sheep farmer. Banks had tried to introduce the Spanish wool breed of sheep, the Merino, on his farm, but with little success; this failure might explain his suspicions of Bakewell, who he suggested was “…promoting his breed by cunning and impudent means.”20 Neither Bakewell nor Banks, nor anyone else at the time, seem to have realized the pro- found theoretical implications of Bakewell’s breeding programme; the simple fact that he Figure 4 | A New Leicester sheep. Robert Bakewell’s famous barrel-shaped breed. Image taken from had created a new race that bred true was all an original painting by A. Churchill, kindly provided by the artist © (2006) A. Churchill. that mattered. That, and the money.

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In the early years of the nineteenth cen- no realization that there was an underlying 100 tury, following Bakewell’s death, the impact common cause of these phenomena25. of his work led directly to new thinking The studies of polydactyly that were car- 80 about heredity. As Roger Wood and Vitěszlav ried out by Maupertuis and Réaumur were 60 Orel have shown20,21, Bakewell’s approach was part of the growing trend for eighteenth- soon applied to wool production, and led to century French physicians to study hereditary 40 the introduction of the Merino into Central diseases (FIG. 4). The initial spur for much of Number of theses Europe, in particular through the efforts of this interest came from a competition that 20 Ferdinand Geisslern in Moravia. Brno — the was organized by the Académie de Dijon in 0 capital of Moravia and known in the nine- 1748, in which thinkers were asked to answer 1700 1800 teenth century as the ‘Austrian Manchester’ the question: “How are hereditary illnesses Year — was a centre for both the textile industry transmitted?”26 Two further discussions were Figure 5 | Number of French medical theses and sheep breeding. Thinkers in the local organized in 1788 and 1790, by the Académie on hereditary illnesses, 1650–1800. Data from scientific and agricultural community began Royale de Médicine, around the question of REF. 11. to try to understand the new techniques they whether any illnesses at all were hereditary, in were using. As early as 1819 they outlined which physicians distinguished between dis- what they called ‘genetic laws’, such as the fact eases that were directly inherited and those Conclusion that grandparental traits could sometimes in which only a predisposition was passed It took humanity a remarkably long time reappear, just as Columella had noticed from generation to generation (FIG. 5). to discover that there are consistent rela- nearly 2,000 years earlier. For practical and As a result of this work, thinkers became tions between parent and offspring, and to theoretical reasons, they also addressed an convinced that there was a force that develop ways of studying those relations. issue that was fascinating plant breeders at expressed itself across the generations, The raw phenomena of heredity were the time22 — the problem of predicting what altering the characters of individuals. The sufficiently complex to be impervious to kind of hybrid would be produced from a reification of this conviction took form, ‘common-sense’ reasoning, to the brilliant cross between two breeds. not only as a growing field of study of but stifling schemas that were developed Although teetering on the brink of insight, pathological characters, but also in the by the Greek philosophers, and even to this work did not immediately lead to a great identification of this force with a noun the stunning forays of the early scientists. breakthrough in our understanding of hered- — ‘heredité’ — which became widespread What was required was not a novel piece ity. However, it had the enormous virtue of from 1830 onwards. The English equivalent of apparatus, nor even a new theory; the creating an intellectual context in the Brno was first used in print by Spencer in 1863, key thing that was needed was statistically region that contributed to Mendel’s interest and was used by Darwin in his notes extraordinary data sets. On the one hand, in heredity and hybridization. In 1837, the around the same time25. Language had these were composed of many reliable purest expression of this interest was shown come into line with thinking, and scientists human pedigrees of unusual or pathologi- by Abbot Napp, who, 6 years later, would and physicians were now convinced that cal characters; on the other, they were the welcome Mendel to the Brno monastery, there were consistent — if bewildering large-scale experimental studies that were when he asked the most important question — relations between parents and offspring. carried out consciously by Mendel, or as a of all: “…what is inherited and how?”21 Once heredity had been recognized, by-product of the commercial activity of the challenge was to turn the conception eighteenth-century livestock breeders. Enter the physicians of heredity as a force into what Jean Gayon Like all great truths, heredity seems Napp was able to ask his question not only has called “…an organizational or structural obvious once it is understood. But the fact because of the patient work of the breeders conception of heredity” — in other words, that so many people took so long to realize and the focused intellectual life in Brno, but a conception in which heredity was based what we take for granted does not mean also because, by this time, it had become on particles23. Mendel’s experiments on that our predecessors were stupid. Instead, apparent that there was a force of heredity hybridization in peas led him to adopt a it indicates that, before the patterns within that could be studied23. As Carlos Lόpez- particulate understanding of heredity in hereditary phenomena could be detected, Beltrán has shown, that conviction, and which some ‘recessive’ particles were not society had to develop to a sufficient level the introduction of the term ‘heredity’ into the expressed, but could reappear in later gen- for these kinds of data to be collected, exam- study of nature, came neither from scientists erations (his insight was made easier by his ined, compared and intepreted. However, nor breeders, but from French physicians. choice of traits with discrete classes; matters although science, written family records and It had long been known that, like might have been different had he measured large-scale agricultural production were the legal rights, some human diseases were a continuous variable). Darwin’s wide read- prerequisites for the discovery of heredity, ‘hereditary’. For example, in the seventeenth- ing of the massive amount of data that were the birth of our science was not simple, and century, the philosopher Sir Francis Bacon produced by breeders led him to also favour required bold thinkers who were prepared to wrote that: “Long Life, is like some Diseases, a particulate approach to heredity, in which resolve an issue that had perplexed humanity a Thing Hereditarie, within certaine some characters were ‘invisible’ or ‘latent’. for thousands of years. The result — the twin Bounds.”24 However, as Bacon indicated, From this point on, the study of heredity fields of genetics and evolution — represents these characters were rarely consistently began to move from a description of tenden- one of the greatest insights in human history. passed down from generation to generation cies and forces to the search for the heredi- Matthew Cobb is at the Faculty of Life Sciences, (“within certaine Bounds”), and above all tary particles that produced characters, University of Manchester, M13 9PT, UK. the lack of a noun (‘heredity’) to go with the interacted and allowed evolution by natural e-mail: [email protected] adjective (‘hereditary’) shows that there was selection — the units of heredity. doi:10.1038/nrg1948

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1. Mueller-Wille, S. & Rheinberger, H.-J. Heredity — the 12. Ratcliff, M. J. in A Cultural History of Heredity I: 22. Stubbe, H. History of Genetics: From Prehistoric Times Production of an Epistemic Space Vol 276 (Max-Planck- 17th and 18th Centuries Vol 222 (Max-Planck- to the Rediscovery of Mendel’s Laws (MIT Press, Institut für Wissenschaftsgeschichte, Berlin, 2004). Institut für Wissenschaftsgeschichte, Berlin, London, 1972). 2. Bowler, P. J. The Mendelian Revolution: The 2002). 23. Gayon, J. in The Concept of the Gene in Emergence of Hereditarian Concepts in Modern 13. Gayon, J. in Lamarck, Philosophe de la Nature Development and Evolution: Historical and Science and Society (Athlone, London, 1989). (eds Corsi, P., Gayon, J., Gohau, G. & Tirard, S.) Epistemological Perspectives (eds Buerton, P., 3. Blackledge, C. The Story of V (Weidenfeld & Nicolson, (Presses Univ. France, Paris, in the press) Falk, R. & Rheinberger, H.-J.) 69–90 (Cambridge London, 2003). (in French). Univ. Press, Cambridge, 2000). 4. Malinowski, B. The Sexual Life of Savages in North- 14. de Maupertuis, P.-L. M. Vénus Physique 24. Bacon, F. Historie Naturall and Experimentall, Western Melanesia (Routledge & Kegan Paul, London, (unknown publisher, 1745) (in French). of Life and Death (Lee & Mosley, London, 1932). 15. Terrall, M. in A Cultural History of Heredity I: 17th and 1638). 5. Furth, C. A Flourishing Yin: Gender in China’s Medical 18th Centuries Vol 222 (Max-Planck-Institut für 25. López-Beltrán, C. Forging heredity: from metaphor to History, 960–1665 (California Univ. Press, Berkeley, Wissenschaftsgeschichte, Berlin, 2002). cause, a reification story. Stud. Hist. Philos. Sci. 25, 1999). 16. Sandler, I. Pierre Louis Moreau de Maupertuis — 211–235 (1994). 6. Cobb, M. The Egg and Sperm Race: The Seventeenth a precursor of Mendel? J. Hist. Biol. 16, 101–136 26. López-Beltrán, C. Les maladies héréditaires: 18th Century Scientists Who Unravelled the Secrets of Life, (1983). century disputes in France. Rev. Hist. Sci. [Paris] 48, Sex and Growth (Free, London, 2006). 17. Blundeville, T. The Fower Cheifyst Offices Belongyng 307–350 (1995). 7. Roger, J. The Life Sciences in Eighteenth-Century to Horsemanshippe (Seres, London, 1566). French Thought (Stanford Univ. Press, Stanford, 1997). 18. Russell, N. Like Engend’ring Like: Heredity and Animal Acknowledgements 8. Harvey, W. Disputations Touching the Generation of Breeding in Early Modern England (Cambridge Univ. Thanks to the two anonymous referees. Animals (Translated by G. Whitteridge) (Blackwell, Press, Cambridge, 1986). Oxford, 1981). 19. Columella, L. J. M. Of Husbandry in Twelve Books Competing interests statement 9. Leeuwenhoek to Wren (16 July 1683) in The Collected (Millar, London, 1745). The authors declare no competing financial interests. Letters of Antoni van Leeuwenhoek Vol. 5 (Swets & 20. Wood, R. J. & Orel, V. Genetic Prehistory in Selective Zeitlinger, Amsterdam, 1957). Breeding: a Prelude to Mendel (Oxford Univ. Press, 10. Drake, J. Anthropologia Nova; or, A New System of Oxford, 2001). FURTHER INFORMATION Anatomy (unknown publisher, London, 1707). 21. Wood, R. J. & Orel, V. Scientific breeding in Central The Egg & Sperm Race web site: 11. Müller-Wille, S. in A Cultural History of Heredity I: Europe during the early nineteenth century: http://www.egg-and-sperm.com 17th and 18th Centuries Vol 222 (Max-Planck-Institut background to Mendel’s later work. J. Hist. Biol. 38, Access to this links box is available online. für Wissenschaftsgeschichte, Berlin, 2002). 239–272 (2005).