I recently became the honorary great-grandfather to a baby boy, and his mom let me hold this beautiful new infant in my arms. The beauty of new life—the well-formed tiny hands and feet and the prospects for this new human’s future got to me. Tears started to roll down my cheeks. Then my doctor mind clicked on and I marveled at the biology behind the process of sexual reproduction. I felt humbled as I realized that, even though the centuries and centuries of rigid creationist doctrine of birth began to break in the late 1600s, the biology of conception was a total mystery to doctors until about 1876.
In 1674 a Dutch cloth merchant, Antonie van Leeuwenhoak, using self-made primitive lenses, spotted moving creatures in drops of water, in scrapings from his teeth, and from virtually any place he looked. Curiosity drove him to look at his own semen and he saw a number of living and moving creatures. At first he associated what he saw with a role in conception, but later changed his mind and decided that he was seeing parasitic micro-animals that just happened to be in the ejaculate.
It took another 200 years to understand that there were two different cells that had to do with fertilization—the spermatozoon in the seminal fluid of the male and the ovum from the female. Oscar Hertwig, a youthful German zoologist with a medical degree, became the first person to witness the process of sexual reproduction. He did so in 1876 by looking into his microscope at the union of a spermatozoon and an egg in sea urchins. He discovered that when one sperm penetrated the egg, a membrane was generated that prevented the entry of other sperm. Dr Hertwig also suggested that there is a chemical substance in the nuclei of the two cells that is responsible for fertilization and the transmission of hereditary characteristics. It was another 60 years before scientists Avery, MacLeod, and McCarty demonstrated that this substance was a nucleic acid, what we now call the DNA.
Just as I thought about the magic of DNA, the little charge in my arms burped and my mind came back to the present. I looked at the baby and at the mother and father. Sexual reproduction: baby William exists because of one egg and one spermatozoon. What a miracle.
—George Szasz, CM, MD
Suggested reading
Dolnick E. The seeds of life: From Aristotle to da Vinci, from sharks’ teeth to frogs’ pants, the long and strange quest to discover where babies come from. Basic books 2017.
O’Connor C. Discovery of DNA as the hereditary material using Streptococcus pneumoniae. Nature Education 2008;1:104
OpenMind BBVA. Science – Leading figures: Oscar Hertwig, the first man to observe sexual reproduction. Accessed 20 March 2023. www.bbvaopenmind.com/en/science/leading-figures/oscar-hertwig-the-first-man-to-observe-sexual-reproduction.
This post has not been peer reviewed by the BCMJ Editorial Board.
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