Introduction

With the microevolutionary theory emerged the concept of a population as an isolated group of conspecific interbreeding individuals who share a gene pool. But human populations present a hierarchy of further isolations. Consanguinity in marriage, where it occurs, serves as an isolating mechanism at the lowest level. Such marriages have important implications for the health and wellbeing of the subsequent generation, and recognition of this led to systematic studies on the rates and patterns of marital consanguinity in different countries. The highest rates so far have been found in Japan, India, Israel and Brazil. But there is wide variability within each country and within local populations. The variability and the trends of consanguineous marriage in Indian populations are mainly determined by the marriage regulations and cultural traditions.

Marriage regulations

The first level of breeding isolation in Indian populations is determined by religious and sect affiliations and linguistic-cultural diversities and traditions. About 75% of the people make up the traditional Hindu society with its network of varnas and endogamous jatis, about 8% belong to more isolated and relatively tradition-bound groups called the scheduled tribes near forests and hills, about 13% belong to Muslim communities, and the rest to Sikh, Christian, Buddhist, Jain, Parsee and Jewish. All of them are distributed over the different provinces and states, with different linguistic or other traditions. These populations originated mainly from indigenous peoples (Hindus) and are divided and subdivided into endogamous occupational, local and cultural units (Mukherjee, 1971).