Some Types of Instability

Abstract

A population can be stable in only one way: by the constancy of its birth and death rates over time, and hence the constancy of its rate of increase. It can be unstable in infinitely many ways: by falling or rising birth rates, by falling or rising death rates, by either birth or death rates rising at some ages and falling at others, by the rise or fall being moderate or rapid, by its being linear, quadratic, or of higher degree. Any and all of these and their combinations could be given the same detailed attention as stability. Needless to say that will not be done here, nor is it likely to be done anywhere else.