Francis Galton ou comment photographier une moyenne

By realising “generic images” or “composite portraits” (images obtained by superimposing several pictures of the same individual or of different individuals belonging to the same family or group) Francis Galton was trying to capture the image of an abstract entity: a type, a statistical average, the “essence” of an individual or the “typical” character of a group. He was trying to eliminate subjectivity from what is usually considered characteristically subjective: the formation of mental images, of abstract concepts. After a few months he had to admit that the idea that certain physical traits could be related to a “type” was wrong (the composite of an “average criminal” is very much the same as the composite of an “average poor person”) and he realized that the law of errors based on an arithmetic average, though useful for statisticians trying to describe the phenomena of life and society, could lead in many cases to “absurdities when the phenomena show significant deviations from normality”. Galton didn’t develop this intuition further but, as was often the case for him, he paved the way for going beyond his own theories.