The rate of living theory revisited.

A rereading of The Rate of Living [Pearl, University of London Press, London 1928] shows that Pearl's thoughts about the meaning of inheritance and heredity, about the relations of between and within populations measurements and about the ways in which life span should be measured are unclear. New ways in which the theory should, eventually, be tested are suggested and the genetic implications of these suggested experimental ways are given. A review is made, mainly in insects, accessorily in rodents, of the different manners in which the theory has been essayed, namely by relating life span with temperature, rate of energy expenditure, growth rate and activity. It is concluded that the theory rests on a weak theoretical basis and even on a series of highly nonplausible assumptions and that, furthermore, the evidence experimentally accumulated is, with a few odd exceptions, not in favor of the theory.