ESHS/HSS Annual Meeting

Pearl’s Prophetic Curve: Graphic Methods of Population Forecasting in the Nineteenth and Twentieth Centuries

• In Event: Data Visualization and the History of Statistics 1

English Abstract

This paper centers on the work of U.S. biologist Raymond Pearl, who in the early 1920s
introduced a ‘biological law of population growth’ that claimed all populations, whether mineral,
vegetable, animal, or human, grow according to the pathway of an S-shaped logistic curve.
Based on this claim, Pearl insisted that his logistic curve could be used as a tool of population
forecasting—considered essential to urban planning, corporate planning, and federal economic
policy. Pearl’s curve was in good company—since the advent of statistical graphing in the late
eighteenth century, innumerable population curves (that is, line graphs depicting a population’s
growth or decline over time) had been created and used to make predictions about the future.
This prognostication was accomplished by fitting a mathematical curve—whether linear,
exponential, or otherwise—to existing population statistics and projecting that curve into the
future. Not exclusive to population forecasting, this method had been used from the late
nineteenth century forward to generate predictions based on any kind of time-series (defined as
sequences of data points collected at regular intervals over time). This paper identifies the
epistemic conditions that made such a method conceivable. I argue, first, that forecasting by
curves depended on both a formalist belief in the inherent expressivity of visual forms and a
historicist faith that the future would resemble the past. And second, I demonstrate that when
applied to populations, in particular, curve-based forecasting relied on tenets of organicism, in
that it presumed a fundamental likeness between populations and individual living organisms.

Author

• Hannah Pivo