differences between socioeconomic classes. They feared that the
lower classes were out-reproducing the “eminent” in society and
predicted that the intellectual ability of the country would decline
unless steps were taken.
In contrast to the socioeconomic focus of those early eugeni-
cists, many American eugenicists came to be preoccupied with race.
Race is an elusive concept in human biology. At one time or
another, it has meant everything from a family to a tribe to a nation
to an entire species. To most adherents of eugenics, however, it was
not mysterious at all. It was an article of faith that the human spe-
cies could be exactly divided into separate races that differed from
each other in inherited characteristics. Here, for example, is the def-
inition of a race proposed by the prominent American eugenicist
Charles B. Davenport (Figure 3):
A race is a more or less pure bred “group” of individuals
that differs from other groups by at least one character,
or, strictly, a genetically connected group whose germ
plasm is characterized by a difference, in one or more
genes, from other groups. (Davenport, 1917)
To Davenport, a “blue-eyed Scotchman” belonged to a different race from “the dark Scotch,” and by a strict genetic criterion
could even be considered members of different “elemental species” (Davenport, 1917).
The attributes that distinguished one race from another were
not merely skin pigmentation and other easily observable physical
traits. The races were also believed to differ in temperament,
behavior, and mental ability. Francis Galton, for example, estimated that the intelligence of blacks was, on average, two “grades”
below that of the average Englishman (roughly equivalent to 20
IQ points; Provine, 1973). An effective program of eugenics
would thus seem to require a prohibition on matings between
the genetically superior whites and genetically inferior blacks.
Such interbreeding was considered equivalent to “mongrelizing”
in thoroughbred horses and other highly bred animals. Most
eugenicists therefore strongly warned of the dangers of “race
crossing.” One of the first was Davenport.
Davenport’s rather haphazard investigations persuaded him
that physical features like eye color, skin color, and hair color
were inherited separately as simple Mendelian characters (
Provine, 1973). In other words, he believed that each trait was controlled by one or two genes, and that each gene had two
alleles, one dominant and the other recessive. He proposed, for
example, that skin color was determined by two genes working
together (Davenport, 1913). After analyzing data collected by
fieldworkers from the Eugenics Record Office, he concluded further that these physical features were inherited independently of
each other. For example, he assumed that it was possible to
inherit a short torso from one parent and long legs from the
other parent (Davenport, 1917).
“Race Crossing” & the Dihybrid Cross
Like most other eugenicists, Davenport believed the races to be
genetically distinct. This, he maintained, was due to thousands of
years of natural selection adapting each race to its environment.
He thought that matings between people of two widely divergent
races, who differed in several Mendelian characters, would produce
“disharmonious” genetic combinations in subsequent generations.
By way of analogy, he gave the example of two breeds of chicken,
Leghorn and Brahma. The Leghorn hen (Figure 4) is an indeterminate egg-layer; it will keep laying new eggs to replace those
removed from the nest. It lacks the brooding instinct, however,
and will rarely sit on a clutch of eggs. In contrast, the Brahma
hen (Figure 5) is only a fair egg-layer and becomes broody two
or three times a year, staying on the nest day and night for up to
three weeks without laying new eggs. Moreover, it excels at mothering its chicks.
Davenport crossed the two breeds and found that the hybrid
hens laid an intermediate number of eggs, but just a day or two after
hatching they stopped mothering the chicks, leaving them to die,
and resumed laying a few days later. The hybrid hens thus failed
both in egg laying and in mothering their chicks. In Davenport’s
words, “the instincts and functions of the hybrids were not harmoniously adjusted to each other” (Davenport, 1917).
With this unsatisfactory cross as an illustrative case, Davenport
turned his attention to “wide race crosses” in humans, with the dihybrid cross as his primary explanatory tool. He cited the example of
Figure3.Ch arles B. Davenport (1866–1944). https://upload.