The male body, followed by male reproductive organs from which the sperm originates, is depicted from top to bottom at the left. Under the male reproductive organs is a diagram of a single sperm. To the right of the sperm diagram, the physiological and morphological changes a sperm undergoes to fertilize an egg are depicted from left to right. Each change is associated with a light pink rectangle background. Each light pink rectangle corresponds to the location of the sperm within the female reproductive organs, which is depicted above it. In addition, a molecular view of each change is directly under each light pink rectangle.
It is important to note the background color of the illustration. A blue to purple gradient depicts the two phases of sperm capacitation: sperm capacitation is in blue, and the acrosome reaction is in purple. It is still unclear where the two phases differentiate and thus a gradient is used as opposed to two distinct colors. The title location for each phase designates the approximate start of each phase.

Ovism was one of two models of preformationism, a theory of generation prevalent in the late seventeenth through the end of the eighteenth century. Contrary to the competing theory of epigenesis (gradual emergence of form), preformationism held that the unborn offspring existed fully formed in the eggs or sperm of its parents prior to conception. The ovist model held that the maternal egg was the location of this preformed embryo, while the other preformationism model known as spermism preferred the paternal germ cell, as the name implies.

This embryology image is a pencil sketch by Nicolaas Hartsoeker, published as part of his 1694 French-language paper entitled Essai de Dioptrique, a semi-speculative work describing the sorts of new scientific observations that could be done using magnifying lenses. Dioptrique was published in Paris by the publishing house of Jean Anisson. The image depicts a curled up infant-like human, now referred to as a homunculus, inside the head of a sperm cell. This sketch is important to embryology because it is one of the most illustrative examples of preformationism, a theory of generation stating that each future member of any given species exists, fully formed though miniscule, within the gametic cells (sperm or eggs) of its parents. This theory was popular among naturalists in the eighteenth century.

Nicolaas Hartsoeker, a Dutch astronomer, optics manufacturer, and naturalist, was born 26 March 1656 in Gouda, Netherlands, and died 10 December 1725. His mother was Anna van der Mey and his father was Christiaan Hartsoeker, a prominent evangelical minister. His major contribution to embryology was his observations of human sperm cells, which he claimed to be the first to see under a microscope. His sketch of the homunculus, a tiny preformed human he believed to exist in the head of spermatazoa, is his lasting scientific legacy in the field of embryology. This sketch was only a minor part of his first publication, Essai de Dioptrique (1694), which dealt primarily with the use of optical lenses in science. In subsequent years the sketch became iconic of the theory of embryological development known now as preformationism. Hartsoeker himself was a vocal adherent of spermist preformationism and is often cited as the originator of the idea.

Preformationism was a theory of embryological development used in the late seventeenth through the late eighteenth centuries. This theory held that the generation of offspring occurs as a result of an unfolding and growth of preformed parts. There were two competing models of preformationism: the ovism model, in which the location of these preformed parts prior to gestation was the maternal egg, and the spermism model, in which a preformed individual or homunculus was thought to exist in the head of each sperm. Preformationism was a widely-held theory by Enlightenment-era scientists, but by the early 1800s, most scientists had abandoned it, in part because higher magnification in microscopes enabled them to see the very earliest stages of embryos as small collections of cells. Prior to preformationism, naturalists who studied embryo development favored the theory of spontaneous generation in lower animals, such as flies, which appeared to arise from manure. In higher animals, however, scientists used the theory of epigenesis put forth by Aristotle, who said that maternal and paternal fluids came together in the uterus and solidified during early gestation into a fetus. Preformationism was the first theory of generation and development that applied to all organisms in the plant and animal kingdoms.

Telomeres are structures at the ends of DNA strands that get longer in the DNA of sperm cells as males age. That phenomenon is different for most other types of cells, for which telomeres get shorter as organisms age. In 1992, scientists showed that telomere length (TL) in sperm increases with age in contrast to most cell of most other types. Telomeres are the protective caps at the end of DNA strands that preserve chromosomal integrity and contribute to DNA length and stability. In most cells, telomeres shorten with each cell division due to incomplete replication, though the enzyme telomerase functions in some cell lines that undergo repetitive divisions to replenish any lost length and to prevent degradation. Cells, and therefore organisms, with short telomeres are more susceptible to mutations and genetic diseases. While TL increases in a subset of sperm cells and longer telomeres may prevent early disintegration of DNA, it may also prevent natural mechanisms of apoptosis, or cell death, from occurring in abnormal sperm.

In 1973, Ronald Ericsson developed the Ericsson method, which is a technique used to separate human male sperm cells by their genetic material. Ericsson, a physician and reproduction researcher, developed the method while conducting research on sperm isolation in Berlin, Germany, in the early 1970s. He found that the sperm cells that carry male-producing Y chromosomes move through liquid faster than the cells that carry female-producing X chromosomes. As a result of his findings, Ericsson suggested suspending a semen sample in a viscous liquid made from albumin protein, and collecting only sperm that quickly pass through the liquid. Shortly after Ericsson described his method, researchers demonstrated that it was effective for sex selection. However, later studies contested those results. Despite that, the Ericsson method is still utilized by couples in 2018 as a means of sex selection and was the first sperm separation technique used in combination with artificial insemination to enable people to select the sex of their children.

In 1984, human genetics and reproduction researcher and physician Joseph D. Schulman founded the Genetics and IVF Institute, an international organization that provides infertility treatment and genetic services to patients. IVF stands for in vitro fertilization, an infertility treatment in which a female egg is fertilized by male sperm outside of the female body. GIVF is headquartered in Fairfax, Virginia, in association with Inova Health System, formerly called the Fairfax Hospital Association, one of the largest regional hospital systems in the United States. GIVF offers multiple infertility and genetic services including IVF, donor egg and donor sperm programs, prenatal genetic diagnostic testing, and sex selection technology. GIVF was one of the first medical facilities in the United States to offer IVF and has innovated other infertility treatments and genetic services.

Sperm capacitation refers to the physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg. This term was first coined in 1952 by Colin Russell Austin based on independent studies conducted by both Austin himself as well as Min Chueh Chang in 1951. Since the initial reports and emergence of the term, the details of the process have been more clearly elucidated due to technological advancements. The recognition of the phenomenon was quite important to early in vitro fertilization experiments as well as the continued understanding of embryology and reproductive biology.