The Effect of Migration on Maximum Opportunity for Selection

Abstract

SummaryThe effect of migration on the maximum opportunity for selection is analysed using koseki data, the Japanese family registration records, of a village population in a small island. When selection intensity is divided into two components, migration greatly influences the variance of the mortality component of the original formula. The difference in selection intensity, with and without allowance for migration, is conspicuous in the recent cohort; the intensity, with a migration component, shows a consistent increase, whereas it declined in the original formula. The implications of this are discussed in the context of the genetic structure of a population of small size, changing rapidly over time.