Behavioural phenotypes in disability research: historical perspectives.

Western medicine has a long history of accounting for behaviour by reducing the body to ultimate explanatory entities. In pre-modern medicine these were invisible "animal spirits" circulating the body. In modern medicine, they are "genes". Both raise questions. The psychological phenotype is defined by human consensus, varying according to time and place, while the genotype's DNA exists in a realm of material reality. There are deep philosophical and methodological problems in linking one realm to the other. Nyhan's original application of the phenotype-genotype pairing merely claimed that the two realms could be matched because of their common susceptibility to statistical treatment. His behavioural example was "stereotypy". It has since extended to include such things as "social cognition" in Turner's syndrome (Skuse), thus revealing increasingly clearly that the two realms are fundamentally and ontologically separate. The problems are not merely epistemological but ethical, since the looseness of psychological categories involves a blurring of the boundaries between behavioural phenotype and social stereotype. The latter may then be underwritten as "real" by being associated, spuriously, with the empirically demonstrable reality of genetic material.