The internal brand of the scarlet

Natural History, March, 1998 by Stephen Jay Gould

Davenport reached this conclusion because he thought that nomadism ran through family pedigrees in the same manner as hemophilia, color blindness, and the other truly sex-linked recessive traits. This status can be legitimately inferred from several definite patterns of heredity. For example, fathers with the trait do not pass it to their sons (since the relevant gene resides on the X-chromosome and males pass only a Y-chromosome only to their sons). Mothers with the trait pass it to all their sons, but none of their daughters, when the father lacks the trait. (Since the feature is recessive, an afflicted mother must carry the gene on both X-chromosomes. She passes a single X to her son, who must then express the trait, for he has no other X-chromosome. But a daughter will receive one afflicted X-chromosome from her mother and one normal X-chromosome from her father; she will therefore not express that trait because the father's normal copy of the gene is dominant.) Davenport knew these rules, so his study didn't fail on this account. Rather, his criteria for identifying nomadism as a discrete and scorable "thing" were so subjective, and so biased by his genetic assumptions, that his pedigree data turned out to be worthless.

Davenport's summary reached (and preached) a eugenic crescendo: "The wandering instinct," he stated, "is a fundamental human instinct, which is, however, typically inhibited in intelligent adults of civilized peoples." Unfortunately, people who possess the bad gene W (the scarlet letter of wanderlust) cannot achieve this healthy inhibition, and they become feckless nomads who run from responsibility by literal flight. The trait is genetic, racial, and undesirable. Immigrants marked by W should be excluded (and many immigrants must be shiftless wanderers rather than brave adventurers), while nomadic natives should be strongly encouraged, if not compelled, to desist from breeding. Davenport concludes:

The new light brought by our studies is this: The nomadic impulse is, in all the cases, one and the same unit character. Nomads, of all kinds, have a special racial trait - are, in a proper sense, members of the nomadic race. This trait is the absence of the germinal determiner that makes for sedentariness, stability, domesticity.

Of course, no one would now defend Davenport's extreme view of single genes determining nearly every complex human behavior. Most colleagues eventually rejected Davenport's theory; he lived into the 1940s, long past the early flush of Mendelian enthusiasm and well into the modern era of understanding that complex traits usually record the operation of many genes, each with a small and cumulative effect (not to mention a strong, and often predominant, influence from nongenetic environmental contexts of growth and expression). A single gene for anger, conviviality, contemplation, or wanderlust now seems as absurd as a claim that one assassin's bullet, and nothing else, caused World War I, or that Darwin discovered evolution all by himself, and we would still be creationists if he had never been born.