Between February 1969 and August 1970 Edward Kollar and Grace Baird, from the University of Chicago in Chicago, Illinois, published three papers that established the role of the mesenchyme in tooth induction. Drawing upon a history of using tissue interactions to understand differentiation, Kollar and Baird designed their experiments to understand how differentiated structures become specified. Their work overturned a widely accepted model that epithelium controls the identity of the structure, a phenomenon called structural specificity. Interactions between epithelium and mesenchyme control the development and differentiation of many parts during embryonic development, including structures like the gastrointestinal tract and hair. Thus, the realization that mesenchyme drives induction and differentiation during epithelio-mesenchymal interactions had far-reaching effects.

Henry Herbert Goddard was a psychologist who conducted research on intelligence and mental deficiency at the Vineland Training School for Feeble-Minded Boys and Girls in Vineland, New Jersey during the early twentieth century. In 1908, Goddard brought French psychologist Alfred Binet and physician Theodore Simon’s intelligence test to the US and used it to investigate intellectual disability in children at the Vineland Training School for Feeble-Minded Boys and Girls. Goddard also wrote a book in 1912 called The Kallikaks: A Study in the Heredity of Feeble-Mindedness, claiming that traits like mental deficiency were heritable traits. His observations and research led Goddard to advocate for sterilization and segregation of the intellectually disabled, which were ideas that reflected the emerging eugenics movement in the US, during the early nineteenth century. Although by the end of his life, psychologists largely dismissed Goddard’s work, schools and the US military used Goddard’s version of Binet and Simon’s intelligence test to identify mental deficiency.

Charles Benedict Davenport, Madison Grant, and Henry Fairfield Osborn founded the Galton Society for the Study of the Origin and Evolution of Man, or the Galton Society, in New York City, New York, in 1918. The Galton Society was a scientific society that promoted the study of humans in terms of race in service to the US eugenics movement. The Galton Society was named in honor of Francis Galton who first coined the term eugenics in 1883. Galton and other eugenics proponents claimed that the human species could improve through selective breeding that restricted who could have children. Some of the society members were scientists from a wide range of disciplines who supported the now disproven notion that fundamental biological differences exist between races that may justify the control of human reproduction. The Galton Society drew on the scientific credibility and influence of its members to advocate for eugenics programs, such as immigration restriction laws, in the US.

The Silent Scream is an anti-abortion film released in 1984 by American Portrait Films, then based in Brunswick, Ohio. The film was created and narrated by Bernard Nathanson, an obstetrician and gynecologist from New York, and it was produced by Crusade for Life, an evangelical anti-abortion organization. In the video, Nathanson narrates ultrasound footage of an abortion of a twelve-week-old fetus, claiming that the fetus opened its mouth in what Nathanson calls a silent scream during the procedure. As a result of Nathanson's anti-abortion stance in the film, The Silent Scream contributed to the abortion debate in the 1980s.

In the early twentieth century, Paul Kammerer conducted a series of experiments to demonstrate that organisms could transmit characteristics acquired in their lifetimes to their offspring. In his 1809 publication, zoologist Jean-Baptiste Lamarck had hypothesized that living beings can inherit features their parents or ancestors acquired throughout life. By breeding salamanders, as well as frogs and other organisms, Kammerer tested Lamarck's hypothesis in an attempt to provide evidence for Lamarck's theory of the inheritance of acquired characteristics. In particular, Kammerer argued that the inheritance of acquired characteristics caused species to evolve, and he claimed that his results provided an explanation for evolutionary processes through developmental phenomena.

In the first decade of the twentieth century, Paul Kammerer, a zoologist working at the Vivarium in Vienna, Austria, conducted research on developmental mechanisms, including a series of breeding experiments on toads (Alytes obstetricans). Kammerer claimed that his results demonstrated that organisms could transmit acquired characteristics to their offspring. To explain how evolution occurred, biologist Jean-Baptiste Lamarck in France suggested in his 1809 book that offspring inherited the features their ancestors acquired throughout the lives of those ancestors, a process termed the inheritance of acquired characteristics. Kammerer conducted breeding experiments to test the theory of inheritance of acquired characteristics, which he said described the mechanics of evolution. Additionally, Kammerer's experiments aimed at explaining how development shaped evolutionary processes.

Sir John Bertrand Gurdon further developed nuclear transplantation, the technique used to clone organisms and to create stem cells, while working in Britain in the second half of the twentieth century. Gurdon's research built on the work of Thomas King and Robert Briggs in the United States, who in 1952 published findings that indicated that scientists could take a nucleus from an early embryonic cell and successfully transfer it into an unfertilized and enucleated egg cell. Briggs and King also concluded that a nucleus taken from an adult cell and similarly inserted into an unfertilized enucleated egg cell could not produce normal development. In 1962, however, Gurdon published results that indicated otherwise. While Briggs and King worked with Rana pipiens frogs, Gurdon used the faster-growing species Xenopus laevis to show that nuclei from specialized cells still held the potential to be any cell despite its specialization. In 2012, the Nobel Prize Committee awarded Gurdon and Shinya Yamanaka its prize in physiology and medicine for for their work on cloning and pluripotent stem cells.

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form. As organs form, a process called organogenesis, mesoderm interacts with endoderm and ectoderm to give rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme. All animals that have only one plane of symmetry through the body, called bilateral symmetry, form three germ layers. Animals that have only two germ layers develop open digestive cavities. In contrast, the evolutionary development of the mesoderm allowed in animals the formation of internal organs such as stomachs and intestines (viscera).

Friedrich Leopold August Weismann published Das
Keimplasma: eine Theorie der Vererbung (The Germ-Plasm: a
Theory of Heredity, hereafter The Germ-Plasm) while
working at the University of Freiburg in Freiburg, Germany in 1892.
William N. Parker, a professor in the University College of South
Wales and Monmouthshire in Cardiff, UK, translated The
Germ-Plasm into English in 1893. In The Germ-Plasm,
Weismann proposed a theory of heredity based on the concept of the
germ plasm, a substance in the germ cell that carries hereditary information. The
Germ-Plasm compiled Weismann's theoretical work and analyses of
other biologists' experimental work in the 1880s, and it provided a
framework to study development, evolution and heredity. Weismann
anticipated that the germ-plasm theory would enable researchers to
investigate the functions and material of hereditary substances.

In the early twentieth century, Paul Kammerer, a zoologist working at the Vivarium in Vienna, Austria, experimented on sea-squirts (Ciona intestinalis). Kammerer claimed that results from his experiments demonstrated that organisms could transmit characteristics that they had acquired in their lifetimes to their offspring. Kammerer conducted breeding experiments on sea-squirts and other organisms at a time when Charles Darwin's 1859 theory of evolution lacked evidence to explain how offspring inherited traits from their parents. In 1809, zoologist Jean-Baptiste Lamarck in France theorized that living beings can inherit the features their parents or ancestors acquired during those ancestor's lifetime, a theory called the inheritance of acquired characteristics. Kammerer attempted to provide evidence for the theory of inheritance of acquired characteristics, which constituted, he argued, the mechanics of evolution. Kammerer claimed that his results could explain evolutionary processes through developmental phenomena.