Harald zur Hausen studied viruses and discovered that certain strains of the human papilloma virus (HPV), a sexually transmitted disease, can cause cervical cancer, in Europe during the twentieth and twenty-first centuries. Zur Hausen spent his research career identifying the viruses that cause diseases, particularly cancer-causing viruses (oncoviruses). He primarily focused on HPV and cervical cancer. Zur Hausen hypothesized that HPV was cancerous and discovered that two strains, HPV 16 and 18, caused cervical cancer. That discovery led to improved diagnosis of cervical cancer and the later development of the HPV vaccines, Gardasil and Cervarix. In 2008, zur Hausen won the Nobel Prize in Physiology or Medicine.

In 1955, obstetrician Edward Bishop, a physician specializing in childbirth, published the article “Elective Induction of Labor,” in which he proposed the best conditions for pregnant women to elect to induce, or begin, labor. Elective induction of labor requires an obstetrician to administer a drug to help a pregnant woman to start her contractions, and to rupture the fluid-filled sac surrounding the fetus called the amniotic sac. In the early 1950s, Bishop analyzed the results of one thousand elective inductions and discovered that some pregnant women had faster and easier deliveries with induced labor than other pregnant women. In “Elective Induction of Labor,” Bishop describes the characteristics an obstetrician can look for in a pregnant woman to determine if she can safely undergo an elective induction, metrics still used into the twenty-first century to determine whether or not to pursue elective inductions.

Karl Oskar Illmensee studied the cloning and reproduction of fruit flies, mice, and humans in the US and Europe during the twentieth and twenty-first centuries. Illmensee used nuclear transfer techniques (cloning) to create early mouse embryos from adult mouse cells, a technique biologists used in later decades to help explain how embryonic cells function during development. In the early 1980s, Illmensee faced accusations of fraud when others were unable to replicate the results of his experiments with cloned mouse embryos. Illmensee also worked with human embryos, investigating how embryos split to form identical twins.

From 1977 to 1987, Harald zur Hausen led a team of researchers across several institutions in Germany to investigate whether the human papillomavirus (HPV) caused cervical cancer. Zur Hausen's first experiment tested the hypothesis that HPV caused cervical cancer rather than herpes simplex virus type 2 (HSV-2), the then accepted cause. His second and third experiments detailed methods to identify two previously unidentified HPV strains, HPV 16 and HPV 18, in cervical cancer tumor samples. The experiments showed that HPV 16 and 18 DNA were present in cervical tumor samples. Zur Hausen concluded that HPV, not HSV-2, caused cervical cancer, which enabled researchers to develop preventions, such as the HPV vaccine.

Berthold Karl Hölldobler studied social insects like ants in Europe and the US during the twentieth and early twenty-first century. He focused on the social behavior of ants, the evolutionary origins of social insects, and the way ants use chemicals to communicate with each other. Hölldobler’s research reached popular audiences through his co-authored Pulitzer Prize winning book The Ants and through an award winning nature documentary called Ameisen: Die heimliche Weltmacht (Ants: Nature’s Secret Power). Hölldobler researched reproductive practices in specific ant species and helped explain how reproductive practices influence, and are influenced by, social behaviors.

In the 1980s, researchers at the pharmaceutical company Roussel-Uclaf in Paris, France, helped develop a biological compound called mifepristone. When a woman takes it, mifepristone interferes with the function of hormones involved in pregnancy and it can therefore be used to terminate pregnancies. In 2000, the US Food and Drug Administration approved mifepristone, also called RU 486, as part of a treatment to induce abortions using drugs instead of surgery, a method called medication abortion. Women can receive medication abortions earlier in their pregnancies than surgical abortions, and medication abortions often result in less severe side-effects than their surgical counterparts. In that capacity, mifepristone has increased women’s access to abortions throughout the world.

Carl Richard Moore was a professor and researcher at the University of Chicago in Chicago, Illinois who studied sex hormones in animals from 1916 until his death in 1955. Moore focused on the role of hormones on sex differentiation in offspring, the optimal conditions for sperm production, and the effects of vasectomy or testicular implants on male sex hormone production. Moore's experiments to create hermaphrodites in the laboratory contributed to the theory of a feedback loop between the pituitary and fetal gonadal hormones to control sex differentiation. Moore showed that the scrotal sac controls the temperature for the testes, which is necessary for sperm production. He also helped distinguish the hormones testosterone, and androsterone from testicular extracts.

Frank Rattray Lillie's research on freemartins from 1914 to 1920 in the US led to the theory that hormones partly caused for sex differentiation in mammals. Although sometimes applied to sheep, goats, and pigs, the term freemartin most often refers to a sterile cow that has external female genitalia and internal male gonads and was born with a normal male twin. Lillie theorized that a freemartin is a genetic female whose process of sexual development from an undifferentiated zygote was suppressed or antagonized by her twin's release of male hormones via their shared blood circulation in utero. Despite publications of similar findings by physician Julius Tandler in Vienna, Austria, in 1910 and physician Karl Keller in Wiesensteig, Germany in 1916 prior to Lillie's research, Lillie often receives credit for the hormonal theory of sex differentiation in the freemartin. Lillie's study of freemartins, and the subsequent research by graduate students in Lillie's laboratory at the University of Chicago in Chicago, Illinois, prompted many embryologists to research sex differentiation and hermaphroditism in mammals.