A population of the West African Green monkey (Cercopithecus aethiops sabaeus) has been established for some 300 years (100 generations) on the West Indian island of St Kitts. Earlier studies carried out between 20 and 30 years ago showed this island population to have greater dental and cranial dimensions, to be less variable in these dimensions, to be more variable in certain meristic dental characters (e.g. supernumerary teeth) and to be less symmetrical in dental and cranial features than the contemporary mainland descendants of the parent West African stock. The extent of divergence in dental and cranial dimensional characters between the West Indian and West African Green monkeys appeared to be on the same general scale as that obtaining between the West African Green monkey and certain other groups of African cercopitheques commonly accorded distinct subspecific or specific status.

These earlier analyses were unavoidably based upon univariate statistical techniques or upon simple derivatives therefrom. Hence, it was not then possible to evaluate correlations between dimensions so that detailed results may conceivably have been influenced by this and by other inescapable factors, e.g. lack of mensural data occasioned by sample limitation and the imperfection of particular specimens. It is also possible, if unlikely, that these earlier results might have been influenced by a systematic computational error, resulting in the variance of bilateral dimensions being increased by a factor of approximately two.

The original data (slightly augmented by newly available material) have been reanalysed by univariate and multivariate techniques designed to overcome former deficiencies, the latter now being deployable because of the availability of computers of adequate power.

Such new analyses have fully substantiated the earlier findings and have given precision to the comparison of the extent of divergence in a total of 73 dental and cranial dimensions between the St. Kitts Green monkey, the African Green monkey and other species and subspecies of Cercopithecus.

The overall divergence in the sum total of dental and cranial dimensions as measured by the generalized distance (a multivariate quantity compounding both size and shape) between three subspecies (sabaeus, pygerythrus and aethiops) of Cercopithecus aethiops has proved to be of the same general scale as that between males and females in Cercopithecus and to be smaller than that between three full species (aethiops, nictitans and cephus) of this genus.

Divergence between the St. Kitts and African Green monkeys in the combination of features has emerged as being generally similar to that between species of the genus Cercopithecus, and bigger than that between subspecies.

Analysis of cranial dimensions alone has given a similar pattern of separation. In contrast, a multivariate compound of dental dimensions has revealed the extent of divergence between subspecies, between sexes as well as between species as being similar, the divergence between the St. Kitts and African population being also of the same general order.

The pattern of dental and cranial divergence between the St. Kitts Green monkey, the African Green monkey and other cercopitheques is similar if factors relating to size are eliminated from the analysis and attention confined to shape only, irrespective of whether or not such components attributable to proportional growth changes (size-dependent shape), or to those which are apparently independent of overall size, are included in the analyses.

Such differences could well betoken a measure of genetic contrast between the present-day St. Kitts and West African Green monkey but the new information elicited in the present study, even when combined with the results of recent studies of the behaviour and sociology of the St. Kitts Green monkey, and of certain aspects of its reproductive biology, does not necessarily form a basis for according the island monkey a taxonomic status distinct from that of the present-day African descendants of its parent stock: Cercopithecus aethiops sabaeus.