7.4 Varieties of physique: a genetic basis of human diversity.
In the animal world we see diverging lines of specialised development. Insects are extremely light in weight and packed with sensory organs that are attached to a well developed nervous system. Birds of prey combine lightness with great strength and striking power. Some mammals, like the sea-cow and hippopotamus, seem specialized in digesting great masses of food and collecting weight in a gregarious social setting. It is tempting to compare the diversity within the human species with that of the animal world. Sheldon and coworkers have done this systematically, with intelligence and humour in the Atlas of Man (1954).
Body types, or somatotypes, express a biological pattern in the long term time-window of form. Related patterns of biological functions and behaviour of the individual are expressed in short term time-windows. Remember that the only difference between adapting form and behaviour is a matter of time-scale (Chapter 2). It is not surprising that a characteristic set of genes expresses itself differently in different time-scales. Factor analysis, applied to measurements of a large human population, has yielded three primary components that determine the human form. The investigators noticed a relation to characteristics of the germ layers, therefore the components that influence the individual physical form or somatotype were named: endomorphy, mesomorphy and ectomorphy. Sheldon's taxonomy of somatotypes derives its value from the fact that experienced observers can distinguish, with a high inter-observer reliability, the amount of influence of any component on a seven-point scale. The cipher 1 stands for a minimal expression of the trait, 7 for its maximal presence.
An example of the notation used is:
somatotype 3 4 4, for a body-type that shows an almost equal distribution of the components endo- meso- and ectomorphy, in that order;
somatotype 1 3 6 would stand for a mesomorphic ectomorph, with very little endomorphy. In everyday language the first example would have a farm horse type of body build, the second would be a spare, sinewy person.
Numerous studies have demonstrated a satisfactory reliability and validity of this approach. Yet the number of researchers in the behavioural, medical and social sciences who have adopted it has remained limited (in the Netherlands: Petersen 1961, Verdonck 1972). One of the reasons is that studies that describe inequality and human diversity are not deemed to be politically correct. The outcome of such studies gives rise to the concern that this will lead to unfair discrimination. Thus a subject of research that has the potential to improve the life conditions of individuals and groups of all ages, is deliberately ignored and left to go waste. Mankind would be better served by the kind of science that seriously takes into account individual talents and aspirations, especially when these are deeply rooted in a persons genetic disposition. At the end of the next chapter we hope to reconcile the two conflicting viewpoints.