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.

In 2007, Françoise Baylis and Jason Scott Robert published “Part-Human Chimeras: Worrying the Facts, Probing the Ethics” in The American Journal of Bioethics. Within their article, hereafter “Part-Human Chimeras,” the authors offer corrections on “Thinking About the Human Neuron Mouse,” a report published in The American Journal of Bioethics in 2007 by Henry Greely, Mildred K. Cho, Linda F. Hogle, and Debra M. Satz, which discussed the debate on the ethics of creating part-human chimeras. Chimeras are organisms that contain two or more genetically distinct cell lines. Both publications discuss chimeras with DNA from different species, specifically in response to studies in which scientists injected human brain cells into mice. “Part-Human Chimeras,” contributes to a chain of ethical and scientific discussion that occurred in the mid-2000s on whether people should be able to conduct research on chimeras, especially in embryos.

In 2006, bioethicist Jason Scott Robert published “The Science and Ethics of Making Part-Human Animals in Stem Cell Biology” in The FASEB Journal. There, he reviews the scientific and ethical justifications and restrictions on creating part-human animals. Robert describes part-human animals, otherwise known as chimeras, as those resulting from the intentional combination of human and nonhuman cells, tissues, or organs at any stage of development. He specifically criticizes restrictions against creating part-human animals made by the National Academy of Sciences, or NAS, in 2005, arguing that while they ensure that such research is morally justifiable, they might limit scientists from conducting useful science using part-human animals or entities. Robert challenges the moral rationales behind prohibiting chimera research, arguing that they may impede scientists from conducting research that could have important benefits to biology and medicine, and suggests how to balance the conflicting moral and scientific needs of such science.

In May 1953, scientists James Watson and Francis Crick wrote the article “Genetical Implications of the Structure of Deoxyribonucleic Acid,” hereafter “Genetical Implications,” which was published in the journal Nature. In “Genetical Implications,” Watson and Crick suggest a possible explanation for deoxyribonucleic acid, or DNA, replication based on a structure of DNA they proposed prior to writing “Genetical Implications.” Watson and Crick proposed their theory about DNA replication at a time when scientists had recently reached the consensus that DNA contained genes, which scientists understood to carry information that determines an organism’s identity. Watson and Crick’s replication mechanism as presented in “Genetical Implications” contributed to the two scientists sharing a portion of the 1962 Nobel Prize in Physiology or Medicine. With their suggested DNA replication mechanism in “Genetical Implications,” Watson and Crick explained how genes are copied and passed along to new cells and organisms, thereby explaining how the information contained within genes is preserved through generations.

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.

Walter Jakob Gehring discovered the homeobox, a DNA segment found in a specific cluster of genes that determine the body plan of animals, plants, and fungi. Gehring identified the homeobox in 1983, with the help of colleagues while isolating the Antennapedia (Antp) gene in fruit flies (Drosophila) at the University of Basel in Basel, Switzerland. Hox genes, a family of genes that have the homeobox, determine the head-to-tail (anterior-posterior) body axis of both vertebrates and invertebrates. Gehring also identified the homeobox-containing Pax-6 gene as the master control gene in eye development of Drosophila, the same gene that, when mutated or absent in humans, leads to aniridia, or lack of the iris, in humans. Gehring's work with the homeobox suggested to biologists that widely different species share a similar and evolutionarily conserved genetic pathway that controls the development of overall body plans, from fruit flies to humans.

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.

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.