Origin: A Genetic History of the Americas

the “father of physical anthropology”—was Philadelphia physician and
scholar Samuel George Morton (1799–1851). Morton believed that skulls
were particularly useful for race science, since they did double duty; he
thought that they both revealed not only a person’s race but also their level
of intelligence. It was a common assumption in the 19th century that cranial
volume must be a direct reflection of intelligence: The bigger the brain, the
smarter the person. (We now know that this is not true.)
Morton built upon Blumenbach’s methodologies and undertook the
study of crania for racial classification on a massive scale, believing that in
addition to volume, a skull’s shape was an essential racial marker. The
cephalic index—the ratio of the maximum width to the maximum length of
the skull—emerged as the simplest and most popular way of categorizing
people into races. People belonged to one of three groups: long-headed
people (dolichocephalic), short-headed people (brachycephalic), and those
whose heads were neither short nor long (mesocephalic). These three types
were referred to as Negroid, Mongoloid, and Caucasoid, respectively.
Morton reasoned that calculating the average cranial sizes of populations
was the best way to assess differences in intellectual capacity between the
races and developed systematic methods for measuring crania to estimate
their volumes. His primary method of calculating cranial volume was to fill
the crania with mustard seed (and then later with lead shot) and record the
amount it took to fill each skull.
On the basis of his measurements, Morton ranked Blumenbach’s types
according to intelligence, with Caucasians at the top and Ethiopians at the
bottom. Morton’s research on the natural inferiority of non-Caucasians was
explicitly used to justify slavery and the theft of land from Native
Americans (26).
But Morton disagreed with Blumenbach about the origins of the races.
Morton believed in polygenism, which explained human variation as the
result of the separate creation of each race, rather than their eventual
formation from the dispersal of the (initially Caucasian) descendants of
Noah’s sons. He was convinced that the differences in cranial size and
shape extended deep into the past of each race; the Great Flood was simply
too recent to account for all these differences. If racial traits were fixed and
unchanging, the implication was that different races were actually separate
species.