Agricultural Systems 36 (1991) 159-171 ~..~:~. v'Ni I Local Adaptation, Varietal Diversity and the Skewness of Regional Crop Yields Hung P. Nguyen Center for Naval Analyses, 4401 Ford Avenue, PO Box 16268, Alexandria, Virginia 22302, USA & Jock R. Anderson Agricultural Policies Division, Agricultural & Rural Development Department, World Bank, 1818 H Street, NW, Washington DC 20433, USA (Received 20 March 1989; accepted 14 November 1990) A BSTRA CT On grounds of theory, anecdote and intuition, it is argued that crop varieties that are well adapted to local conditions will tend to have negatively skewed yield distributions. Conversely, when varieties are widely adopted that do not feature close local adaptation, and varietal diversity is substantially reduced, yields may tend to be other than negatively skewed. These arguments are supported by data on yields of different crops in different environments around the world. Analogous arguments concerning the degree of optimality o]" the crop-growng environment and the state of technological achievement of an agriculture are also similarly addressed. As the degree of control in an environment increases, yields again tend to be negatively skewed in contrast to those environments which are regulated but sub-optimal, where positive skewness tends to be encountered. INTRODUCTION The rapid adoption of high-yielding and 'broadly adapted' varieties is displacing locally adapted cultivars throughout the developing world. 159 Agricultural Systems 0308-521 X/91/$03.50 (~ 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain