INTRODUCTION

The scenarios discussed in this paper are based on my own work during the last 25 years, supplemented with studies of other investigators, and made possible through collaboration with many colleagues. To these persons, too numerous to mention here, I am deeply indebted.

Our investigations have been concerned with people of many different ethnic origins, covering a wide geographical area, from India and Sri Lanka in the west, through Malaysia, Thailand, Indonesia, and New Guinea, to the central Pacific in the east. Population structures of the peoples studied range also from small tribal enclaves within larger communities, or isolated island populations through to populations with well defined social castes of wide dispersal. The genetic variability is equally varied, and the genetic relationships between these populations is complex, being a compound of diversity of origins, migration and intermixture, and adaptation to particular environments. Certainly we do not yet fully understand this complexity, but we have unravelled some part of it, enough now to see what needs to be studied further.

These studies have covered human populations in the tropics. This does not mean that all live in a uniform environment. Their habitats vary from tropical rain-forest to desert, from sea level to several thousand metres elevation. Their economic base likewise covers hunter-gatherers, slash and burn cultivators, to settled agriculturalists and urban dwellers. Sometimes ecological differences are broadly based, as in India and South-East Asia, sometimes they occur within a small geographic area.

India and South-East Asia

For India and South-East Asia there are broad ecological zones.