TinyChan

The many studies of selective breeding in various species of mammals provides conclusive evidence that many behavioral characteristics, just as most physical characteristics, can be manipulated by genetic selection (see Fuller - Thompson, 1962; Scott and Fuller, 1965). Rats, for example, have been bred for maze learning ability in many different laboratories. It makes little difference whether one refers to this ability as rat "intelligence," "learning ability" or some other term- we know that it is possible to breed selectively for whatever the factors are that make for speed of maze learning. To be sure, individual variation in this complex ability may be due to any combination of a number of characteristics involving sensory acuity, drive level, emotional stability, strength of innate turning preferences, brain chemistry, brain size, structure of neural connections, speed of synaptic transmission, or whatever. The point is that the molar behavior of learning to get through a maze efficiently without making errors (i.e., going up blind alleys) can be markedly influenced in later generations by selective breeding of the parent generations of rats who are either fast or slow ("maze bright" or "maze dull," to use the prevailing terminology in this research) in learning to get through the maze. Figure 4 shows the results of one such genetic selection experiment. They are quite typical; with only six generations of selection the offspring of the "dull" strain make 100 percent more errors in learning the maze than do the offspring of the "bright" strain (Thompson, 1954). In most experiments of this type, of course, the behaviors that respond so dramatically to selection are relatively simple as compared with human intelligence, and the experimental selection pressure is severe, so the implications of such findings for the study of human variation should not be overdrawn. Yet geneticists seem to express little doubt that many behavioral traits in humans would respond similarly to genetic selection. Three eminent geneticists (James F. Crow, James V. Neel, and Curt Stern) of the National Academy of Sciences recently prepared a "position statement," which was generally hedged by extreme caution and understatement, that asserted: "Animal experiments have shown that almost any trait can be changed by selection. ... A selection program to increase human intelligence (or whatever is measured by various kinds of 'intelligence' tests) would almost certainly be successful in some measure. The same is probably true for other behavioral traits. The rate of increase would be somewhat unpredictable, but there is little doubt that there would be progress" (National Academy of Sciences, 1967, p. 893).

FIGURE 4.
The mean error scores in maze learning for successive generations of selectively bred "bright" and "dull" strains of McGill rats. (After Thompson, 1954.)