PEARL, RAYMOND

(1879–1940)

Raymond Pearl was an American biologist, geneticist, biometrician, and eugenicist. He was also a professor of Biometry and Vital Statistics at Johns Hopkins University (1918–1940) and the first president of the International Union for the Scientific Investigation of Population Problems (IUSSP's predecessor). Pearl studied under the statistician Karl Pearson (1857–1936) in London and subsequently applied statistical methods to the analysis of human populations, concentrating on longevity, fertility, and the patterns of population growth. The value used in the medical sciences to rate the effectiveness of a birth control method bears his name (Pearl Index). Following the lead of the eugenicist Francis Galton and Pearson, Pearl tried to create a new branch of mathematical biology–the "biology of groups"–based on the population as the unit of analysis.

Under the influence of Pearson, Pearl started out as a strong advocate of eugenics. However, in the course of his active life, he relaxed his views, arguing against the class bias that pervaded the eugenics movement. Much to the chagrin of the eugenicists he asserted that the higher reproduction rate of the lower classes need not be feared: the lower classes often produced superior individuals who, given the opportunity for social mobility, would become valuable members of society.

In 1920 Pearl, together with Lowell J. Reed, rediscovered the "logistic curve" of population growth, which had been first formulated by the Belgian mathematician Pierre-François Verhulst in 1838. Initially, Pearl tended to interpret the logistic curve in a deterministic way as a general biological "law," holding for both human and non-human populations. In his view the theoretical basis for this was to be found in natural causes–biological, physical or chemical. The relevance of the logistic curve as a theory of population growth was widely questioned by those who thought that such growth depended largely upon cultural, social, and economic changes. Later, Pearl moved away from determinism.

Both Pearl and his law of logistic population growth were prominent at the World Population Conference in Geneva in 1927. Throughout the 1920s the merits of the logistic curve as a tool for estimating and projecting population growth were debated and juxtaposed with those of the cohort component approach then being introduced. The latter method was favored by most European statisticians and economists, and subsequently became the dominant mode of population forecasting. In 1932 Alfred Lotka reconciled the two approaches by constructing a unified formal model that integrated the logistic and cohort-component characteristics of population growth.

BIBLIOGRAPHY

SELECTED WORKS BY RAYMOND PEARL.

Pearl, Raymond. 1924. Studies in Human Biology Baltimore, MD: Williams & Wilkins.

——. 1926. The Biology of Population Growth. London, Williams and Norgate.

——. 1928. The Rate of Living: Being an Account of Some Experimental Studies on the Biology of Life Duration. New York: Alfred A. Knopf.

——. 1939. The Natural History of Population. New York: Oxford University Press.

Pearl, Raymond, and Lowell J. Reed. 1930. The Logistic Curve and the Census Count of 1930. New York: Science Press.

SELECTED WORKS ABOUT RAYMOND PEARL.

De Gans, Henk A. 2002. "Law or Speculation? A Debate on the Method of Forecasting Future Population Size in the 1920s." Population 57(1): 83–108.

Kingsland, Sharon. 1988. "Evolution and Debates Over Human Progress from Darwin to Sociobiology." In Population and Resources in Western Intellectual Traditions, ed. Michael S. Teitelbaum and Jay M. Winter. Supplement to Population and Development Review, Vol. 14, pp.167–189.

Lotka, Alfred J. 1932. "The Structure of a Growing Population." In Problems of Population. London: George Allen and Unwin Ltd.