For many years, the process of fertilization was a mystery to biologists. It was not until the late nineteenth century, when the science of microscopy had begun to take off, that scientists began to observe and understand the chemical and biological processes that occurred within the human body, both before and after insemination.

It is now known that fertilization cannot occur until the (male) sperm and the (female) egg, or ovum, are brought together. In many aquatic and amphibian species, the eggs are released by the female, while the male deposits his sperm on or near them; however, in most mammalian species (including humans), the male uses a special organ to deposit the sperm safely within the female. The sperm then swims randomly until it dies or encounters an egg.

Once the sperm and egg meet, the fertilization process can begin. As the tip of the sperm touches...