1. Intelligence of Bushmen
There have been only three studies of the intelligence of the Bushmen. In the 1930s a sample of 25 of them were intelligence tested by Porteus (1937) with his maze test, which involves
tracing the correct route with pencil through a series of mazes of increasing difficulty. The test has norms for European children for each age, in relation to which the Bushmen obtained a mental age of seven and a half years, representing an IQ of approximately 48. In the second study, Porteus gave the
Leiter International Performance Scale to 197 adult Bushmen and concluded that their mental age was approximately 10 years, giving them an IQ of 62. In the third study, Reuning (1972), a South African psychologist, tested 108 Bushmen and 159 Africans with a pattern completion test involving
the selection of an item to complete a pattern. In the light of his experience of the test, Reuning concluded that it "can be used as a reliable instrument for the assessment of intelligence at the lower levels of cognitive development and among preliterate peoples" (1968, p. 469). On this test the Bushmen scored approximately 15 IQ points below the Africans, and since it is known that Africans have a mean IQ of approximately 67 (see Chapter 4), this would give the Bushmen an IQ of approximately 52.
Reuning also gave
a figure drawing test involving the drawing of a man to the Bushmen and the Africans. This test is the same as the Goodenough Draw-a-Man test (DAM), which is a reasonably good measure of intelligence. The drawings produced in the Goodenough Test are scored for detail and sophistication, which improve as children grow older. Young children typically draw stick men with little detail, while older children draw full-bodied men with many details such as eyebrows, thumbs, and so on. Reuning (1968, p. 476) recorded that the Bushmen's drawings were significantly less advanced than those of Negroid mineworkers, whom he also tested and 76 percent of whom were illiterate. He described the Bushmen's drawings as characterized by "extreme simplicity...the majority were stick figures...no details of fingers, toes, hair, eyes, etc...." The simplicity of the Bushmen's drawings "contrasts with the tendency of the blacks to include much small detail in their drawings (buttons, hair, fingers, toes, a pipe, etc.)." The difference between Bushmen and Africans in the sophistication of drawings provides further corroboration of the lower intelligence of Bushmen.
Reuning noted that there was considerable variability in intelligence between individuals among the Bushmen, just as there is among other peoples, and that
they themselves recognize that some individuals are intelligent while others are dull. Their languages have the word "clever" to describe this attribute. He records that "When the tester at the end of a test had praised a good performance, they let us know, through the interpreter: 'We could have told you so, he (or she) is clever' (1968, p. 479). There is, furthermore, a general factor (g) among the Kalahari Bushmen shown by the positive intercorrelation of a number of tests and
the correlation between test performance and the general consensus of who is intelligent. In addition to administering a test of intelligence, Reuning tested Bushmen and comparison groups of Africans and whites for size constancy. This is the ability to estimate the size of an object at a distance. He found that Bushmen had more accurate size constancy than Africans and Europeans and attributed this to the need for this ability for using the bow and arrow for hitting an animal at a distance. He found that Bushwomen also have good size constancy although they do not hunt. He suggests that the development of this ability is probably attributable to its advantage for efficient hunting. If this is correct, it implies that the ability may have deteriorated in European and East Asian peoples who gave up hunting about 8,000 years ago and adopted agriculture.
The three studies of Bushmen by Porteus and Reuning give IQs of 48, 62, and 52 and
can be averaged to give an IQ of 54. It may be questioned whether a people with an average IQ of 54 could survive as hunter-gatherers in the Kalahari desert, and therefore whether this can be a valid estimate of their intelligence. An IQ of 54 is at the low end of the range of mild mental retardation in economically developed nations. This is less of a problem than might be thought. The great majority of the mildly mentally retarded in economically developed societies do not reside in hospitals or institutions but live normal lives in the community. Many of them have children and work either in the home or doing cognitively undemanding jobs.
An IQ of 54 represents the mental age of the average European 8-year-old child, and the average European 8-year-old can read, write, and do arithmetic and would have no difficulty in learning and performing the activities of gathering foods and hunting carried out by the San Bushmen. An average European 8-year-old can easily be taught to pick berries, put them in a container and carry them home, collect ostrich eggs and use the shells for storing water, and learn to use a bow and arrow and hit a target at some distance. Before the introduction of universal education for children throughout North America and Europe in the second half of the nineteenth century, the great majority of 8-year-old children worked productively on farms and sometimes as chimney sweeps and in factories and mines. Today, many children of this age in Africa, India, Pakistan, Bangladesh, through out much of Latin America, and in other economically developing count tries work on farms and some of them do semi-skilled work such as carpet weaving and operating sewing machines. There is a range of intelligence among the Bushmen and most of them will have IQs in the
range of 35 to 75. An IQ of 35 represents approximately the mental age of the average European five-and-a-half-year-old and an IQ of 75 represents approximately the mental age of the average European eleven-and-a-half-year old. The average five-and-a-half-year-old European child is verbally fluent and is capable of doing unskilled jobs and the same should be true for even the least intelligent Bushmen.
Furthermore, apes with mental abilities about the same as those of human 4-year-olds survive quite well as gatherers and occasional hunters and so also did early hominids with IQs of around 40 and brain sizes much smaller than those of modern Bushmen.
For these reasons there is nothing puzzling about contemporary Bushmen with average IQs of about 54 and a range of IQs mainly between 35 and 75 being able to survive as hunter-gatherers and doing the unskilled and semi-skilled farm work that a number of them took up in the closing decades of the twentieth century.
2. Brain Size
The brain size of the Bushmen was estimated at 1,250cc by Drennan (1937) and a little higher at 1,270cc by Smith and Beals (1990). The Smith and Beals data set also includes Negroid Africans whose brain size is 1,282cc and therefore a little larger than that of Bushmen.
This is consistent with the higher average IQ of Africans at 67, as compared with the 54 of Bushmen, although the brain size difference of this magnitude
can only explain a small fraction of the intelligence difference. The smaller brain size and lower intelligence of the Bushmen compared with the Africans implies that the brain size of the Africans increased over the last 100,000 years or so, since contemporary Africans and Bushmen came from the same ancestral stock. Their brain sizes must have originally been the same and that of the Africans must have increased either as a
result of stronger selection pressure or advantageous mutations. 
