Physical Measurements 

& Intelligence
Early attempts to understand intelligence utilized unrefined examinations of group differences among people’s physical structure. Investigators primarily examined these areas by studying group averages for skull capacity or actual brain size.
Samuel George Morton (1799 -1851)
Morton was Philadelphia physician who collected and examined1,849 skulls of Americans. Most of these skulls came from the various Native American tribes that had once inhabited the land. Morton believed that a ranking of the races could be established objectively by looking at the cranial capacity of the skulls. He used his detailed research on cranial capacity to support his theory of intellectual superiority of different racial groups.
Stephen Jay Gould (1981) criticized his work with four general problems:

(1) He chose to include/delete sub-samples of skulls form his calculations based on how they fit his theory;

(2) He measured skull capacity with seeds which is inaccurate and subject to bias; re-measurements with more precise tools indicated that Caucasians were typically over-estimated and African Americans were underestimated;

(3) He assumed that cranial size indicated intelligence and didn’t considered the impact of one physical stature or gender on the skull size; & 

(4) He miscalculated rounding estimates that consistently favored his hypothesis.
Cranial Capacity (IN3 )
People Morton's Reported Means Gould's Corrected Mean
Mongolian 83 87
Modern Caucasian 92 87
Native American 84 86
Malay 85 85
Ancient Caucasians 84 84
African Americans 83 83
Dr. Paul Broca (1824-1880)

 
 

Broca was a chief of surgery at a major Parisian hospital who was interested in the variations found among people’s skeletal structures, particularly their skulls.He developed several instruments for measuring these variations.

When questioned about the connection between brain size and intelligence, Broca replied

In general, the brain is larger in mature adults than in elderly, in men than in women, in eminent men than in men of mediocre talent, in superior races than in inferior races (1861, p. 304)… Other things equal, there is a remarkable relationship between the development of intelligence and the volume of the brain (p. 188).
Dr. Broca’s examination of brain size was influenced by his desire to demonstrate physical evidence for his belief that Caucasian males were intellectually superior to women and men of other races. For example:

1) When Broca found that criminals mean brain size was larger than honest people’s average brain size, he dismissed this information stating that the executions caused the brain structure to change. 

2) When Gratiolet (an opponent of the belief that brain size was correlated with intelligence) indicated that French brains were smaller than German brains, Broca correctly adjusted the German brain sizes to account for differences in body stature.However, he did not use this type of adjustment when he examined the differences between men and women’s brain sizes.

3)When he found results that didn’t support his theory, he abandoned his exploration in the area.

 
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