The internal brand of the scarlet

Natural History, March, 1998 by Stephen Jay Gould

The deepest error of this third category lies in the reductionist and really rather silly notion that we can even create rigorous definitions for discrete, separable, specific traits within the complex continua of human behaviors. We have enough trouble specifying characters with clear links to particular genes in the much clearer and simpler features of human anatomy. I may be able to specify genes "for" eye color but not for leg length or fatness. How then shall I parse the continuous and necessarily subjective categories of labile personalities? Is novelty seeking really a "thing" at all? Can I even talk in any meaningful way about "genes for" such nebulous categories? Have I not fallen right back into the errors of Davenport's search for the internal scarlet letter W of wanderlust?

I finally realized what had been troubling me so much about the literature on "genes for" behavior when I read the Times's account of C. R. Cloninger's theory of personality (Cloninger is the principal author of the Nature Genetics "News and Views" feature):

Novelty seeking is one of four aspects that Dr. Cloninger and many other psychologists propose as the basic bricks of normal temperament, the other three being avoidance of harm, reward dependence and persistence. All four humors are thought to be attributable in good part to one's genetic makeup.

The line about "humors" crystallized my distress, for I realized why the canny reporter (or the scientist himself) had used this old word. Consider the theory in outline: four independent components of temperament, properly in balance in "normal" folks, but with each individual displaying subtly different proportions, thus determining our personal temperaments and building our distinct personalities. But if one humor gets out of whack by substantial over- or under-representation, then a pathology may result.

But why four, and why these four? Why not five, or six, or six hundred? Why any specific number? Why try to parse such continua into definite independent "things" at all? I do understand the mathematical theories and procedures that lead to such identifications (see my book The Mismeasure of Man), but I regard the entire enterprise as a major philosophical error of our time (while I view the mathematical techniques, which I use extensively in my own research, as highly valuable when properly applied). Numerical clumps are not physical realities. A four-component model of temperament may act as a useful heuristic device, but I don't believe for a moment that four homunculi labeled "novelty seeking," "avoidance of harm," "reward dependence," and "persistence" reside in my brain, either wing for dominance or cooperating.

The logic of such a theory runs in uncanny parallel - hence the clever choice of "humor" as a descriptive term for proposed modules of temperament - with the oldest and most venerable of gloriously wrong theories in the history of medicine. For more than a thousand years, from Galen to the dawn of modern medicine, prevailing concepts regarded the human personality as a balance among four humors - blood, phlegm, choler, and melancholy. Humor, from the Latin word for liquid (preserved in our designation of the fluids of the human eye as the aqueous and vitreous humors), referred to the four liquids that supposedly formed the chyle, or digested food in the intestine just before it entered the body for nourishment. Since the chyle arose, on one hand, from a range of choices in the food we eat and, on the other hand, from constitutional differences in how various bodies digest this food, the totality recorded both innate and external factors - an exact equivalent to the modern claim that both genes and environment influence our behavior.