For many centuries notions of human reproduction were based on the ideas formulated long before the beginning of the first millennium by two Greek authorities, Hippocrates (460-377 bc) and Aristotle (380322 bc). In his book De Semine (On Semen) the former wrote that both male and female seminal fluid was formed in the brain and subsequently reached the genitalia via the spine. When both substances united in sexual intercourse, this would produce a child that would inherit the characteristics of either the father or the mother, depending on which of the seminal fluids provided by the father and mother was more powerful. According to Hippocrates the sex of the child was also determined by the strength of the seminal fluid.
While Hippocrates assigned a more or less equal role to the man and the woman, Aristotle took a different view. Of course he could not help admitting some female input and so argued that woman’s sole contribution was to provide what he called catamenia. This was residual menstrual blood that constituted transformed matter and could basically produce nothing until the man added his seed. The drawings of Leonardo da Vinci (1452-1519) show his brilliant mind still clinging to the idea that seminal fluid came straight from the brain. Leonardo drew two ducts in the penis, one for the passage of urine and one for seminal fluid. The white seminal fluid came like mother’s milk directly from the backbone. Leonardo was interested not only in helicopters, but also in reproduction. In the Royal Gallery at Windsor there is a cross-section drawn by him of a man and woman having intercourse. Above the sketch he wrote, in his familiar mirror writing: ‘I show people the first, or perhaps second reason for their existence.’ For
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his anatomical drawings he used animals such as oxen as a model. This led him astray: he forgot to draw the prostate, which is understandable, since in the case of castration before puberty that organ develops scarcely if at all. Even a genius like Leonardo, then, got it wrong not once, but twice.
One of the many researchers who tackled the mystery of procreation was William Harvey (1578-1657), the discoverer of the circulation of the blood. After his appointment as Physician Extraordinary to King James i he concentrated his research on the growth of the embryo in chickens’ eggs and on the uteri of deer from the Royal Deer Park. In 1651, at the age of 73, he published his research findings. In contrast to the views then current, Harvey asserted that animals and human beings came from an egg, with the exception of insects, which, he maintained, were generated ‘spontaneously’ from waste matter. The latter was Aristotle’s ancient notion, to which Harvey adhered in another respect too: he ascribed the development of the embryo to the vital forces in the male sperm.
Aristotle’s ideas on spontaneous generation in insects and other invertebrates were made less plausible by the investigations of a physician at the court of Tuscany, Francesco Redi (1626-1697), which demonstrated that flies lay eggs in meat waste. The starting point for his studies was a passage of Classical poetry. In Book xix of Homer’s Iliad, Achilles is worried that the flies in the wounds of his slain friend Patroclus will produce worms. Redi examined exactly what Homer meant and observed that after a while worms (i. e. maggots) emerged from meat on which flies had settled. No worms appeared where insects had no access. He used an amazing range of different meats: ox, venison, buffalo, lion, tiger, dog, lamb, kid, rabbit, duck, goose, chicken, swallow, swordfish, tuna, eel, tongue, etc. The result was always the same, and he drew the conclusion that insects were not produced by rotting waste matter, but also came from eggs, which the mother laid in the meat for nutriment.
The celebrated anatomist Frederik Ruysch (1638-1731) was equally sceptical that fertilization could take place ‘solely through the vapours and spirits of the male seed’. ‘I am well aware that in sexual congress the larger part of the seed flows away, but I am convinced that the viscous seed remaining in the womb is sufficient to bring about fertilization.’ Ruysch had found the uterine cavity and the two ‘trumpets’ (Fallopian tubes) filled with a very large quantity of male seed. This was most unusual: Harvey had never been able to find seed in the uteri of deer, but Ruysch had found it in women. (In the 1970s Harvey’s findings were examined in the light of modern knowledge by Professor Roger Short, who also made a remarkable film replicating Harvey’s
research. In hindsight it was no wonder that Harvey did not discover how reproduction actually functioned, mainly because this is much less transparent in deer than in most other animals. And of course without a microscope it was very difficult for him to detect sperm in the uteri of the hinds he dissected shortly after mating.)
One day Ruysch had a unique opportunity. He was commissioned by the Amsterdam municipal authorities to write a report on a murder. The victim was a prostitute, whose throat had been cut by a young man with whom she had just had intercourse. After establishing the cause of death, Ruysch satisfied his scientific curiosity, with three doctors in attendance. He cut open the victim’s abdomen, ‘being most curious to see what would appear in the womb and those parts made for conception. I therefore removed the womb, the Fallopian tubes and their appendages very carefully from the body,’ he noted. The cervix was closed, but when he pressed gently with his finger it opened and sperm came out. He then opened the womb and found more sperm. Both tubes were also full of it. He preserved the material in his ‘balsamic’ fluid, which caused the sperm to harden and stabilize. Subsequently it could serve as scientific evidence.
Later Ruysch had a further opportunity to gather first-hand evidence. This time it involved the body of a wife caught in the act with her lover and stabbed to death by her husband. Ruysch was called in to perform a post-mortem examination, and when he found the womb somewhat more ‘elevated’ than normal, he suspected that fertilization had taken place. He then removed the womb from the body for further examination, and found her lover’s sperm not only in the uterine cavity, but also in both Fallopian tubes.
Ruysch’s assumption was that if the seed itself were not necessary to effect fertilization, the tubes would not be full of sperm. When asked, most women had told him that when they became pregnant they usually had the feeling that most of the sperm had remained in their bodies. ‘What else is one to believe than that the substances of nature, and not only their vapours or spirits are required for this work,’ observed Ruysch. The question of whether the sperm contained tiny creatures, which also played a part, he left unresolved.
For centuries Aristotle’s view on the predominant role of the male in reproduction obviously had a great appeal for many people, including another scientist, Antonie van Leeuwenhoek (1632-1723). Using candlelight and ground glass he had made his own microscope. He was actually a cloth merchant by trade and also ran a draper’s shop, where he sold buttons and ribbons. In the back room behind the shop he became a self-trained scientist. He taught himself glass-blowing, grinding and
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polishing and was subsequently able to produce high-quality lenses. During his lifetime he ground over five hundred, including some with a magnification of approximately 480X. No one knows why Van Leeuwenhoek started using the microscope. Perhaps he wanted to take a close look at textiles, or he may have simply revelled in his own ingenuity and skill. His simple microscope was not much more than a wooden frame containing a small glass globe, made by extending a thin length of red-hot glass until a globule separated from it which after cooling was polished smooth. It was certainly not easy to use the apparatus. Endless peering, from very close range, and preferably in bright sunlight, soon led to tired eyes. Van Leeuwenhoek had an additional problem: he could not draw at all. For this reason he employed a number of draughtsmen, who made illustrations for him.
A Leiden professor was very interested in the cloth merchant’s work. He introduced a relative of his, the student Johan Ham, to Van Leeuwenhoek. On his second visit, in 1677, Ham brought with him the sperm of a man with the clap. He had seen tiny creatures moving about in it and assumed that their presence was connected with the man’s disease. He asked Van Leeuwenhoek to take a look with his microscope. A few years before, at the request of a foreign scholar, Van Leeuwenhoek had put spittle, sweat and sperm under his microscope and at that time had seen something resembling tiny globules in the sperm, but had not pursued his observations because he found them distasteful. Now he was urged by the student to repeat the investigation. Van Leeuwenhoek felt extremely uncomfortable. The reason was that in his follow-up studies he used his own sperm and to avoid accusations of sinful behaviour felt obliged to explain that the observations had been carried out on sperm left over after sexual relations with his wife Cornelia. On another occasion he reported that he had placed the sperm under the microscope within ten seconds of ejaculation. His research showed that the creatures Johan Ham had seen were also found in fresh, healthy sperm. He called them spermatozoa. On the basis of ancient metaphysical writings he thought initially that he saw portions of microscopic homunculi, tiny male creatures swimming about in the seminal fluid. On 3 December 1677, not feeling entirely sure of himself, he wrote to the Royal Society in London: ‘If your Harvey and our De Graaf had seen a hundredth part of what I have seen, they would have agreed with my finding that the man’s seed forms the embryo by itself, and all the woman can contribute is to receive or nourish the male seed.’ And in so doing he in fact confirmed what the Greek playwright Aeschylus (525-456 bc) had written many centuries before: ‘The mother of what is called her child, is not its parent, but only the nurse of the young life sown in her.’
Van Leeuwenhoek lived to be ninety and continued with microscopic research until his death in August 1723, fifty years after his introduction to the Royal Society by Reinier de Graaf (1641-1673). His daughter sent his collection of microscopes and specimens to London, where it eventually disappeared, so that only a few of his better microscopes survive in museums, where visitors are usually more interested in the silver slides and the adjustment knob than in the most important component: the tiny glass globule that served as a lens. With his microscopes Van Leeuwenhoek had found the answer to the problem Harvey and Reinier de Graaf had wrestled with: semen played a direct physical role in reproduction, the reason being that spermatozoa could find their way to the womb. He had dismissed the views deriving from, for instance, the work of Redi, Jan Swammerdam (1637-1680) and De Graaf, in which the ovum played a central role in reproduction. Van Leeuwenhoek had focused on the male aspect, while the others had had looked mainly at the female side.
The argument on the question as to what was more important: the ovum or the spermatozoon, between ovists and animaculists (also called spermists) was not finally decided until the second half of the nineteenth century, in 1875 to be exact. In that year the German anatomist Wilhelm Hertwig (1849-1922) showed in an animal experiment that fertilization comes about through the merging of the nuclei of the ovum and the spermatozoon. The exact process was revealed only in 1944, when John Rock of Harvard University put a human ovum in a dish and added a drop of living human sperm. After placing this mixture in human blood serum, Rock was the first person to observe the division of the fertilized ovum into two, the beginning of a strange process that some nine months later results in the birth of a new human being.
Today we know that the female ovum contains more than half the information necessary for the future human being. It provides not only 23 nuclear chromosomes to complement the 23 from the spermatozoon, but also the cytoplasmatic dna located in the mitochondria, the genes of which derive exclusively from the mother. The mitochondria are simply tiny power stations in the cell. This fact torpedoes the arrogant notion that the father is most important in reproduction. More of that anon!