Certain traits, such as intelligence and mental deficiency, have been the focus of eugenic research and propaganda. This focus on such eugenic traits builds on three commonsense ideas: (1) People differ with respect to some of their traits, such as eye-colour and height; (2) Many traits run in families, being passed on from parents to their children; (3) Some traits are desirable, while others are undesirable. These three ideas about traits—their variability, heritability, and desirability—fed the much more controversial eugenicist view that some traits make a person of “good stock”, while others reflect the fact that she comes from “inferior stock”.

In combination with the power to influence human reproduction, the systematic study of eugenic traits has thus been thought to provide the basis for human improvement across generations. Three sources reveal which traits were considered important to eugenicists, the public, and decision makers: the research publications of eugenicists, discussions of eugenics in public and popular media, and legislation.

Research publications
The research publications of proponents of eugenics include Francis Galton’s studies of genius, the “white trash” family studies that began with Richard Dugdale’s The Jukes in 1877, and the systematic research undertaken by the Eugenics Record Office (ERO) at Cold Spring Harbor under the direction of Charles Davenport from 1910. The investigation of family histories was central to all three, despite the fact that each study focused on different traits.

Galton’s focus was on family lineages of positive achievement, showing that judges, statesmen, musicians, and wrestlers were found statistically clustered in British families, and inferring that this was due to underlying natural abilities and their transmission. By contrast, the family studies initiated by The Jukes focused on poverty, criminality, and other social problems, applying family pedigree construction to these traits.

The ERO sought to establish a more robust picture of eugenic traits through both research and public advocacy. The ERO quickly sought to build a sweeping analytic index of traits in the US population through family studies. Based on Charles Davenport’s The Trait Book, by 1918 the ERO had amassed over 500,000 index cards charting the flow of eugenic traits through families, concentrating on traits regarded as deleterious or socially problematic, and approximately 1,000,000 such cards by the time the ERO closed in 1939. In addition to the mental and social traits described in eugenic laws (see below), this research also investigated the genealogy of putative personality traits (e.g., rebelliousness, liveliness, and nomadism) as well as physical and physiological traits (e.g., diabetes, stature, and colour blindness).

Public Discussions and the Popular Media
In public discussions and popular media coverage of eugenics, eugenics was often advocated in terms of the threat posed to present and future society by the following sorts of people: the unfit, the feeble-minded, defectives, criminals, paupers, and prostitutes. Some of these traits, such as feeble-mindedness, are explicitly dispositional, in that they are intrinsic tendencies of a person that are responsible for a range of behaviours or actions. Other traits, such as criminality, a person possesses because she engages in certain behaviours or actions. In general, however, behavioural traits were typically thought of as at least implicitly conceived as dispositional: criminals, prostitutes, and paupers, for example, were themselves thought to be sorts of people with distinctive, inherent tendencies.

Legislation
Eugenic legislation includes sterilization laws as well as laws governing immigration and marriage. While the particular lists of eugenic traits can vary from one jurisdiction to another, certain central traits feature pervasively across such legislation.

For example, North American sterilization legislation, introduced between 1905 and 1945, included the following eugenic traits: idiocy, imbecility, feeble-mindedness, epilepsy, insanity, mental illness, mental defectiveness or disease, moral depravity or perversity, sexual depravity or perversity, incestuousness, pedophilia, syphilis, neurosyphilis, criminality, alcoholism, and Huntington’s chorea. Despite variation by state and province, these cluster into two chief groups of traits: those concerning mental deficiency or illness, and those concerning sexualized criminality. Perhaps surprisingly, legislation occasionally did not refer to specific eugenic traits. Instead, it simply authorized eugenics boards to sterilize inmates of mental hospitals (e.g., Alberta 1928), or persons residing in appropriate institutions (e.g., North Carolina 1919).

Immigration laws motivated by eugenic concerns often restricted immigration on the basis of both mental deficiency and sexualized criminality. But the most prominent restrictions on immigration were based on race, ethnicity, and country of origin. For example, the Chinese Immigration Act of 1923 prohibited the immigration of people of “Chinese origin or descent” into Canada; the United States’ Immigration Restriction Act of 1924 targeted putatively dysgenic Italians and eastern European Jews, effectively reducing their immigration quotas three-fold.

Like immigration restriction laws, laws prohibiting marriage between people of different racial or ethnic heritage were fueled by fear of the dysgenic consequences of “race-mixing” or miscegenation. By 1915, when eugenics was gaining steam as a social movement in the United States, 28 states had laws prohibiting or annulling the marriage of “Negroes and white persons”. The Nuremberg Laws of 1935 in Nazi Germany included a law that prohibited marriage and sexual relations between Jews and non-Jews. This Law for the Protection of German Blood included specific restrictions in terms of the categories full Jew, half-Jew, and quarter-Jew, and was later generalized to hold for non-Aryans more generally. Like immigration restriction laws, marriage restriction laws were given a putative scientific basis by eugenicist researchers and propagandists.

The Transmissibility of Eugenic Traits
Pro-eugenic thinking focuses on improving the putative quality of present and future human populations and on interventions that promote that quality. Eugenic traits were viewed as transmissible from present to future generations, typically through some kind of hereditary process tied to reproduction. For this reason, eugenic views about the transmission of traits to, and changes in, future generations are often characterized as being genetic. Indeed, a small number of eugenic traits (e.g., Huntington’s disease) have been demonstrated to be genetically transmitted.

While many eugenics researchers and propagandists did appeal to the genetics of sexual reproduction and disease, eugenics also relied on broader notions of heredity and intergenerational transmission. Three considerations are relevant here.

First, robust and relatively fixed lists of eugenic traits pre-date, by forty years, the origin of genetics in the first decade of the twentieth century. Second, included in lists of eugenic traits were characteristics (such as epilepsy) whose genetic and even biological status was unclear, as well as those (such as tuberculosis) whose primary cause was known at the time to be non-genetic. Third, eugenic thought and practice was sufficiently motivated from the 1860s by conceiving of eugenic traits as being subject to simplistic principles, such as that “like begets like”.

Conclusion: From Commonsense to Social Movement
The commonsense idea that desirable and undesirable traits run in and vary across families underpins much eugenic thinking. Putting that thought into practice generated various lists of eugenic traits. Here the pedigree studies conducted and promoted by Davenport’s Eugenics Record Office over a 30-year period played an important role in shifting eugenics from ideology to social movement. While the most prevalent eugenic traits found in North American sterilization legislation cluster under two headings—mental deficiency and sexualized criminality—race and ethnicity were also the basis for eugenic restrictions on immigration and marriage.

-Robert A. Wilson

• Allen, Garland, E. (1986). The eugenics record office at Cold Spring Harbor, 1910-1940: an essay in institutional history." Osiris 2, 225-264.

• Davenport, Charles. (1912). The trait book. Eugenics Record Office Bulletin No.6.

• Galton, Francis, (1865). Hereditary talent and character." Macmillan's Magazine, 12, 157-66 & 318-27.

• Galton, Francis. (1869). Hereditary genius. London: MacMillan and Company.

• Lombardo, Paul. (n.d.). Eugenic laws against race mixing." Marriage Laws. Retrieved from http://www.eugenicsarchive.org/eugenics/list2.pl.

• Proctor, Robert. (1988). Racial hygiene: medicine under the Nazis. Cambridge, MA: Harvard University Press.

• Rafter, Nicole (ed.). (1988). White trash: the eugenic family studies, 1877-1919. Boston, MA: Northeastern University Press.

• The Sexual Sterilization Act of Alberta, 1928. Available from www.ourfutureourpast.ca/law/page.aspx?id=2906151.

• O’Brien, Gerald. (2013). Framing the moron: the social construction of feeble-mindedness in the American eugenic era. Manchester: Manchester University Press.