Hermaphrodites and the Medical Invention of Sex, by historian of science Alice Domurat Dreger, was published in 1998 by Harvard University Press. In the book, Dreger describes how many doctors and scientists treated human hermaphrodites from the late nineteenth century to the early twentieth century. She states that during this time period, many physicians and scientists struggled to determine the nature sex, and to support a classification of sex as male or female, many physicians and scientists resorted to viewing a person's gonads for identification of his or her sex. At the time that this book was published, Dreger was a faculty associate at the Center for Ethics and Humanities in the Life Sciences at the College of Medicine, University of Michigan, Michigan.

Gordon Watkins Douglas researched cervical cancer, breach delivery, and treatment of high blood pressure during pregnancy in the US during the twentieth century. He worked primarily at Bellevue Hospital Center in New York, New York. While at Bellevue, he worked with William E. Studdiford to develop treatments for women who contracted infections as a result of illegal abortions performed throughout the US in unsterile environments. Douglas also established the first contraception and pregnancy termination clinic at Bellevue Hospital shortly after the legalization of abortion as a result of the 1973 US Supreme Court ruling in Roe v. Wade. Furthermore, Douglas showed that fetal and maternal cells exchange between the pregnant woman and fetus during pregnancy, which led to the later development of non-invasive prenatal testing in the early twenty-first century.

Neurocristopathies are a class of pathologies in vertebrates,
including humans, that result from abnormal expression, migration,
differentiation, or death of neural crest cells (NCCs) during embryonic development. NCCs are cells
derived from the embryonic cellular structure called the neural crest.
Abnormal NCCs can cause a neurocristopathy by chemically affecting the
development of the non-NCC tissues around them. They can also affect the
development of NCC tissues, causing defective migration or
proliferation of the NCCs. There are many neurocristopathies
that affect many different types of systems. Some neurocristopathies
result in albinism (piebaldism) and cleft palate in humans. Various
pigment, skin, thyroid, and hearing disorders, craniofacial and heart
abnormalities, malfunctions of the digestive tract, and tumors can be
classified as neurocristopathies. This classification ties a variety of
disorders to one embryonic origin.

Early in the process of development, vertebrate embryos develop a fold on the neural plate where the neural and epidermal ectoderms meet, called the neural crest. The neural crest produces neural crest cells (NCCs), which become multiple different cell types and contribute to tissues and organs as an embryo develops. A few of the organs and tissues include peripheral and enteric (gastrointestinal) neurons and glia, pigment cells, cartilage and bone of the cranium and face, and smooth muscle. The diversity of NCCs that the neural crest produces has led researchers to propose the neural crest as a fourth germ layer, or one of the primary cellular structures in early embryos from which all adult tissues and organs arise. Furthermore, evolutionary biologists study the neural crest because it is a novel shared evolutionary character (synapomorphy) of all vertebrates.

In 1995 and 1996, researchers at the Roslin Institute in Edinburgh, Scotland, cloned mammals for the first time. Keith Campbell, Jim McWhir, William Ritchie, and Ian Wilmut cloned two sheep, Megan and Morag, using sheep embryo cells. The experiments indicated how to reprogram nuclei from differentiated cells to produce live offspring, and that a single population of differentiated cells could produce multiple offspring. They reported their results in the article 'Sheep Cloned by Nuclear Transfer from a Cultured Cell Line' in March 1996. This experiment led the Roslin team to later clone mammals from adult body cells and to genetically engineer mammals.

The Report of the Committee of Inquiry
into Human Fertilisation and Embryology, commonly called the Warnock
Report after the chair of the committee Mary Warnock, is the 1984
publication of a UK governmental inquiry into the social impacts of
infertility treatment and embryological research. The birth of Louise
Brown in 1978 in Oldham, UK, sparked debate about reproductive and
embryological technologies. Brown was conceived through in vitro
fertilization (IVF), a process of fertilization that occurs outside of
the body of the woman. At the time IVF was largely unregulated in the
UK, both in law and within the protocol of the National Health Service
(NHS), headquartered in London, UK. The Warnock Report recommended, and
is credited with, establishing a governmental organization to regulate
infertility treatments such as IVF and embryological research in
general. In 1990, the UK established this governmental organization as
the Human Fertilisation and Embryology Authority (HFEA) in London.

The Roslin Institute was established in 1993 in the village of Roslin, Scotland, as an independent research center by the Biotechnology and Biological Sciences Research Council (BBSRC), and as of 2014 is part of the University of Edinburgh in Edinburgh, Scotland. Researchers at the Roslin Institute cloned the Dolly the sheep in 1996. According to the Roslin Institute, Dolly was the first mammal to develop into an adult from the transfer of the nucleus of an adult sheep cell into an ovum with the nucleus removed. The Roslin Institute performs genetic and medical based animal studies to help investigate human physiology and medicine and to improve agricultural research. The Roslin Institute studies embryology, cloning, hormones, and genetic alterations in animals and techniques such as Somatic Cell Nuclear Transfer (SCNT).

On 9 July 1990, in Moore v. Regents of the University of California, the Supreme Court of California ruled in a four-to-three decision that individuals do not have rights to a share in profits earned from research performed on their bodily materials. In its decision, the Supreme Court of California ruled that cancer patient John L. Moore did not have personal property rights to samples or fluids that his physicians took from his body for research purposes. Moore created the precedent in California that although physicians are required to disclose their research interests to their patients, patients do not have property-related claims to any samples that their physicians take from their body. The Supreme Court of California’s decision in Moore v. Regents of the University of California enabled physicians and researchers to retain legal ownership on samples taken from their patients’ bodies so that they can conduct what the court describes as socially important medical research, such as work on reproductive cancers or developmental disorders.

Francois Jacob studied in
bacteria and bacteriophages at the Institut Pasteur in Paris, France,
in the second half of the twentieth century. In 1965, Jacob won the
Nobel Prize in Physiology or Medicine with Andre M. Lwoff and
Jacques L. Monod for their work on the genetic control of enzyme
synthesis. Jacob studied how genes control and regulate metabolic
enzymes in the bacterium Escherichia
coli (E. coli) and in lysogenic
bacterial systems. He contributed to theories of transcriptional gene
regulation, the operon model, and the distinction between structural
and regulatory genes. Jacob also introduced the concept of
bricolage (tinkering) in evolutionary biology.

Nikolai Ivanovich Vavilov proposed theories of plant genetic diversity and participated in the political debate about genetics in Soviet Russia in the early twentieth century. Vavilov collected plant species around the world, building one of the first and most comprehensive seed banks, and he spent much of his life researching plant breeding and genetics. Vavilov also developed a theory of the historical centers of origin of cultivated plants. Vavilov spent most of his scientific career in Russia, although he studied abroad and traveled extensively. The ascent of geneticist Trofim Lysenko, favored by Joseph Stalin, and Vavilov's public criticism of him lead to Vavilov's arrest in 1940 and his death in prison three years later.