Introduction

Isolation can occur in human populations as a result of different mechanisms. Some are purely ecological, some are of social origin. In the West Indies, the genetic barriers are generally based on a social, economic and political contrast between the « White » and the « Black » segments of the population. In the small island of « La Désirade », close to Guadeloupe, the genetic barrier originates only in the perception of phenotypical differences, inside an homogeneous socio-economic group. It is very difficult to observe any kind of clear racial discrimination in the island. White colour, and some of the phenotypical characteristics connected with « white » people are attributed a strong positive value, independent of any correlation with the social status. 

In « La Désirade », we are very close to a model in which color has a great autonomy with respect to social inequalities, commonly associated in the Caribbean with racial status. In such a situation, the phenotype is not only the marker of identity, but it is also the main support for the biological persistance of a small group of « white » people. Operating through the cognitive level, mating choice, as reflected in the genealogies, enables the survival of an informal endogamous group. 

What is the impact of such a situation on Desirade's genetic structure ? How is the cognitive level reflected both in genealogies and at genetic level ? Does a social value attached to a phenotype correlate with the genetic basis of a phenotype, in such a way that « the biological and social dimension are so intertwined as to be practically inseparable » (HARRISON, 1985, p. 14) ? It is our hope that a combination of biological and social data will help to explain their interaction.