The Discovery of Egg and Sperm in the 17th Century - Phenix-Vet

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The Discovery of Egg and Sperm 5reasons that remain obscure (Ford 1985). Although themicroscope had been invented at the beginning of the17th century, they were generally little better thanmagnifying glasses (Ruestow 1995; Wilson 1995). Thepower of this instrument was brought to public attentionin 1665 when Robert Hooke (1635–1703) publishedhis magnificent book Micrographia, complete withstunning illustrations (the full text of this amazing workcan be found on the internet). But Hooke used acompound microscope, which was very difficult to focus,as Samuel Pepys (a member of the Royal Society)discovered when he bought one of these new-fangleddevices having been impressed by Hooke’s book (‘themost ingenious book that I ever read in my life’). To hisdisappointment, Pepys found it very difficult to seeanything like the images printed by Hooke, and he feltthat the princely sum of £5 10s he had spent on themicroscope was wasted (Tomalin 2002).The single-lens microscope was far easier to construct– it simply involved polishing a tiny glass ball approximately1 mm across – and it was widely adopted in theDutch Republic, with some of its main practitionersincluding Swammerdam, who saw red blood cells anddrew the first cell divisions in a fertilized frog egg, andthe great philosopher Benedict Spinoza (Ruestow 1995).Leeuwenhoek’s long career as a pioneer microscopistwas encouraged by Henry Oldenburg, who publishedLeeuwenhoek’s first letter in the Philosophical Transactionsand then, in 1674, wrote that letter to Leeuwenhoek,inviting him to turn his attention to thecomposition of various bodily fluids, including semen(Cole 1930). Over the next few years, Leeuwenhoek senta number of letters to London, amazing his readers withdescriptions of tiny ‘animalcules’ in water (these wereprotists and large bacteria) (Leewenhoecks (sic) (1677).Then, in autumn 1677, a young medical student fromLeiden, Johann Ham, brought Leeuwenhoek some pusmixed with semen to examine. Ham claimed that thishad been produced by a ‘friend’ who had ‘lain with anunclean woman’. When Ham had looked at the sampleunder his microscope, he had noticed many ‘animalcules’in it; alarmed or enthused (it is not clear which),Ham brought the sample to Leeuwenhoek, who confirmedthe observation and did the obvious thing: helooked at his own semen. To his amazement, Leeuwenhoeksaw there were millions of tiny animalculesthrashing about in the sample. These things wereeventually given the name by which they are still knowntoday, and which completely misclassifies them: ‘spermatozoa’– semen animals.Three months later, Leeuwenhoek dispatched a carefullyworded letter to London, written in Latin, insistingthat should the society consider it ‘either disgusting, orlikely to seem offensive to the learned, I earnestly begthat [it] be regarded private and either published orsuppressed as your Lordship’s judgement dictates’(Leeuwenhoek 1678). In a process that will be familiarto modern readers, the Royal Society then sat onLeeuwenhoek’s earth-shattering discovery. Oldenburghad died a few months earlier, and there was a hiatus inthe offices of the Philosophical Transactions. The neweditor, Nehemiah Grew, had his doubts about Leeuwenhoek’sfindings and eventually wrote back in January1678 asking him to look at the semen of dogs, horsesand other animals. Two further letters from Delftfollowed with the requested observations, but theymerely added to Leeuwenhoek’s previous findings. Thelack of urgency suggests that no one at the RoyalSociety understood why Leeuwenhoek’s discovery wasso important (they do not appear to have considered it‘disgusting’). Leeuwenhoek’s letter was finally publishedin January 1679, nearly 18 months after his initialdiscovery (Leeuwenhoek 1678).Leeuwenhoek’s letter makes clear that he thought thatthe spermatozoa were merely another example of the‘animalcules’ he could see everywhere he pointed hismicroscope. He was much more interested in a tangledmass of tiny vessels which he saw in ‘the denser substanceof the semen’. This structure led Leeuwenhoek to claimwithout the slightest evidence that ‘it is exclusively themale semen that forms the foetus and that all the womanmay contribute only serves to receive the semen and feedit’. In other words, Aristotle had been right all along. Theexact nature of the mass of vessels remains obscure –Leeuwenhoek later admitted that it was ‘merely accidental’(Leeuwenhoek 1683). Whatever the case, Leeuwenhoekdid not immediately grasp the significance of hisdiscovery of animalcules in semen.Other people were far more astute than either Leeuwenhoekor the Royal Society, and realized that theanimalcules themselves were highly significant. Prior topublication, news got out about what Leeuwenhoek hadseen. A few months after Leeuwenhoek’s original observation,in January 1678, Swammerdam wrote a letter toThe´venot stating that he had observed ‘innumerable smallworms’ in mouse and dog semen (Lindeboom 1975). Evenmore importantly, in the summer of 1678 – over 6 monthsbefore the Royal Society published Leeuwenhoek’s letter– Huygens printed a brief account of the study in theJournal des Sçavans, which concluded: ‘This latestdiscovery, which has been made in Holland for the firsttime, seems to me to be extremely important and willprovide material for those who seriously study thegeneration of animals’ (Huygens 1678).150 Years of ConfusionA naive modern reader could reasonably assume thatthis was the end of the matter and that everyone soonrealized that egg and sperm were complementary, eachcontaining half of what was necessary to produce newlife. Not at all. Firstly, there were technical issues: noone had yet seen a human egg, and would not do so until1827 (Von Baer 1956). But above all, it was not clearwhat the discoveries meant. For nearly 150 years,thinking about generation was dominated by either‘ovist’ or ‘spermist’ views (Pinto-Correia 1997; Roger1997). Each approach considered that only one of thetwo parental components provided the stuff of whichnew life was made, with the other component was eitherfood (as the spermists saw the egg), or an immaterialforce that merely ‘awoke’ the egg (as the ovists saw thespermatozoa).There were many reasons underlying this apparentscientific dead end. For example, in chickens the twoelements did not seem to be equivalent at all: there was aÓ 2012 Blackwell Verlag GmbH
6 M Cobbsingle, enormous egg which was apparently passive, whilethe ‘spermatic animals’ were microscopic, incrediblyactive and present in mind-boggling numbers. Ultimately,however, the reason why late 17th-century thinkers didnot realize what to us seems blindingly obvious – that bothegg and sperm make equal contributions to the futureoffspring – was that there was no compelling evidence tomake them appreciate this.It was not until the 19th century that the requisitecombination of evidence and theory came together. Tounderstand the complementary nature of egg and sperm,scientists needed to have a theory that could explain thatcomplementarity. This came in two forms in the earlydecades of the 19th century (Cobb 2006b). The developmentof ‘cell theory’ by Schleiden and Schwann gavean explanation for why egg and sperm were equivalent,despite their manifold differences – they were bothreproductive cells. The other factor was that realizationthat heredity had a biological content and that somethingwas inherited, which was contained in egg andsperm, respectively. This development came aboutthrough the conjunction of three areas: the work ofagro-industrialists such as Robert Bakewell, who carriedout massive selective breeding programmes on domesticatedanimals; the studies by thinkers such as Maupertuisand Re´aumur, who explored large and complexfamily trees in the light of particular characters; and byFrench physicians who studied the inheritance ofdiseases (Cobb 2006b). This was finally given form ina monastery in Brno, where Gregor Mendel was just oneof many people thinking about the nature of heredity.Oddly enough, by the time that the fusion of egg andsperm was observed for the first time, by Hertwig andFol in the late 1870s, it was almost an anti-climax.People thought it was obvious. Which in a way, it was,but getting to such a point had been anything butstraightforward, and would not have occurred withoutthat exciting spasm of discovery in the 17th century.Conflicts of interestNone of the authors have any conflicts of interest to declare.ReferencesAnonymous, 1679: Gaspari Bartholini Th.Filii De Ovariis mulierum & generationishistoria Epistola Anatomica. Journal desScavans , 63–64.Birch T, 1756–7: The History of the RoyalSociety of London for Improving ofNatural Knowledge. Millar, London.Cobb M, 2006a: The Egg and Sperm Race:The Seventeenth Century Scientists WhoUnravelled the Secrets of Life, Sex andGrowth. Free Press, London.Cobb M, 2006b: Heredity before genetics: ahistory. Nat Rev Genet 7, 953–958.Cole FJ, 1930: Early Theories of SexualGeneration. Clarendon, Oxford.De Graaf R, 1668: De Vivorum OrganisGenerationi inservientibus de Clysteribuset de usu Siphonis in Anatomia. Hack, Leiden.De Graaf R, 1671: Epistola ad virum clarissimumD. Lucam Schacht. In: de GraafR (ed.), Tractatus Anatomico-Mdeicus deSucci Pancreatici Natura & Usu. Hak,Leiden, pp. 209–216.De Graaf R, 1672: De Mulierum OrganisGenerationi Inservientibus. Hack, Leiden.De Graaf R, 1673a: Partium GenitaliumDefensio. Hack, Leiden.De Graaf R, 1673b: Letter to Oldenburg (18April 1673). In: Hall AR, Hall M (eds),1973: The Correspondence of Henry Oldenburgvol 9. University of WisconsinPress, Madison, pp. 603.DobellC,1932:AntonyvanLeeuwenhoekandhis ‘‘Little Animals’’. Constable, London.Ford BJ, 1985: Single Lens: The Story of theSimple Microscope. Harper & Row,New York.Furth C, 1999: A Flourishing Yin: Gender inChina’s Medical History, 960–1665. CaliforniaUniversity Press, Berkeley.Hall MB, 2002: Henry Oldenburg: Shapingthe Royal Society. Oxford UniversityPress, Oxford.Harvey W, 1651: Exercitationes de GenerationeAnimalium. Jansson, Amsterdam.Huygens C, 1678: Extrait d’une lettre de M.Huygens de l’Académiie R. des Sciences àl’auteur du journal, touchant une nouvellemanière de microscope qu’il a apporté deHollande. Journal des Sçavans, 331–332.Jocelyn HD, Setchell BP, 1972: Regnier deGraaf on the human reproductive organs.J Reprod Fertil Suppl 17, 1–222.Leeuwenhoek A, 1678: Observationes D.Anthonii Lewenhoeck, de natis è seminigenitali animalcules. Phil Trans R SocLond B 12, 1040–1043.Leeuwenhoek A, 1683: An abstract of aLetter from Mr. Anthony Leewenhoeckwrit to Sir C.W. Jan. 22. 1682 ⁄ 3 fromDelft. Phil Trans R Soc Lond B 13, 74–81.Leewenhoecks (sic), 1677: Monsieur Leewenheocksletter to the publishere, whereinsome account is given of the manner ofhis observing so great a number of littleanimals in divers sorts of water, as wasdeliver’d in the next foregoing Tract:English’d out of Dutch. Phil Trans RSoc Lond B 12, 844–846.Lindeboom GA (ed.), 1975: The Letters ofJan Swammerdam to Melchisedec Thévenot.Swets & Zeitlinger, Amsterdam.Luyendijk-Elshout AM, 1965: Introduction.In: Ruysch F Dilucidatio Valvorum inVasis Lymphasticis et Lacteis (Facsimile).De Graaf Nieuwkoop, The Netherlands,pp. 7–49.Pinto-Correia C, 1997: The Ovary of Eve:Egg and Sperm and Preformation. Universityof Chicago Press, London.Potts M, Short R, 1999: Ever Since Adamand Eve: The Evolution of Human Sexuality.Cambridge University Press,Cambridge.Redi F, 1668: Esperienze Intorno alla GenerazioneDegl’insetti. Stella, Florence.Roger J, 1997: The Life Sciences in Eighteenth-CenturyFrench Thought. StanfordUniversity Press, Stanford.Ruestow EG, 1995: The Microscope in theDutch Republic. Cambridge UniversityPress, Cambridge.Short RV, 1977: The discovery of the ovaries.In: Zuckerman S, Weir BJ (eds), TheOvary, Volume 1: General Aspects. AcademicPress, New York, pp. 1–39.Short RV, 1978: Harvey’s conception: ‘Degeneratione animalium’, 1651. In: DickinsonCJ, Marks J (eds), Developments inCardiovascular Medicine. MTP, Lancaster,pp. 353–363.Steno N, 1668: Elementorum MyologiaeSpecimen. Stella, Florence.Swammerdam J, 1669: Historia InsectorumGeneralis, ofte Algemeene Verhandelingvan de Bloedeloose Dierkens. Van Dreunen,Utrech.Swammerdam J, 1672a: Miraculum Naturae,sive Uteri Muliebris Fabrica. SeverinusMatthei, Lieden.Swammerdam J, n.d. 1672b: Exquisita Demonstratio.Vasorum Spermaticorum,Testium sive Ovarii, Tubarum seuCornuum, &c. n.p., n.p.The´venotM,1665:LettertoHuygens(24April1665). In: Huygens C (ed.), 1977: OeuvresComplètes de Christiaan Huygens vol 5.Swets Zeitlinger, Amsterdam, pp. 343.Tomalin C, 2002: Samuel Pepys: The UnequalledSelf. Penguin, London.Van Horne J, 1668: Observationum suarumCirca Partes Generationis in UtroqueSexu Prodromus. Gaasbekios, Leiden.Von Baer KE, 1956: On the genesis of theovum of mammals and of man. Isis47, 117–153.Wilson C, 1995: The Invisible World. PrincetonUniversity Press, Princeton.Author’s address (for correspondence):M Cobb, Faculty of Life Sciences, Universityof Manchester, Oxford Road, ManchesterM13 9PT, UK. E-mail: cobb@manchester.ac.ukÓ 2012 Blackwell Verlag GmbH
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The Discovery of Egg and Sperm in the 17th Century - Phenix-Vet

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