On Comparative Longevity in Man and the Lower Animals

On Comparative Longevity In Man And The Lower Animals by Edwin Ray Lankester. This 1870 inquiry surveys the longevity of diverse life forms, from protozoa and insects to mammals and humans, through the lens of biological and evolutionary theory. Lankester defines longevity as the duration of life of an individual, and distinguishes between normal potential longevity, absolute potential longevity, and average longevity. He argues that longevity is influenced by two broad factors: high individuation (complexity and bulk) and the level of expenditure (personal and generative). By analyzing 'milieu' and hereditary factors, the essay explores how environment, reproduction, and metabolism shape life-spans, and explains why conditions of civilization can extend or shorten life. The work surveys existing authorities (Bacon, Flourens, Hufeland, Spencer, Darwin) and synthesizes then-modern ideas with inductive evidence, including tables and lists of observed durations in animals, plants, and human groups. A central claim is that longevity in a species is balanced by available resources and the costs of life—growth, maintenance, and reproduction—and that humans, unlike other animals, can modify external conditions to lengthen or curtail life. The latter part applies these ideas to humanity's longevity in different civilizations, as well as the possibility of abnormal longevity. The treatise closes with cautious notes on the limits of data and the need for further study.