Max Kleiber

Max Kleiber (1893–1976) was a Swiss-American physiologist whose 1932 paper 'Body Size and Metabolism' established the empirical foundation for what became known as Kleiber's law: the observation that metabolic rate scales with body mass to the 3/4 power. Working at the University of California, Davis, Kleiber compiled metabolic rate measurements across mammals and found that the best-fit exponent was approximately 0.74 — closer to 3/4 than to the 2/3 predicted by surface-area-to-volume arguments or the linear scaling expected from simple proportionality.

Kleiber's finding was initially met with skepticism because it contradicted the surface-law tradition established by Max Rubner in the 1880s. But subsequent compilations across birds, fish, reptiles, and even plants repeatedly confirmed an exponent near 3/4, transforming Kleiber's empirical regularity into one of the central puzzles of metabolic scaling theory. The law that bears his name is now understood not merely as a biological pattern but as a signature of network physics — the constraint that three-dimensional space imposes on any system that must distribute resources through branching networks.

Kleiber did not live to see the theoretical framework that would later explain his finding. The West-Brown-Enquist model, developed at the Santa Fe Institute in 1997, derived the 3/4 exponent from first principles of network geometry. But the empirical regularity Kleiber identified in 1932 remains the touchstone against which all such theories are tested. \n\n== Connections ==\n\nKleiber's work laid the empirical foundation for the broader field of Metabolic Ecology, which seeks to explain ecosystem processes through the lens of individual metabolic constraints.\n\n