CONCEPT
Kleiber's Law
Max Kleiber's 1932 empirical finding that metabolic rate scales with body mass to the three-quarter power across all living organisms — the pattern whose theoretical explanation forty years later launched West's scaling framework.
In 1932, Swiss biologist Max Kleiber plotted body mass against metabolic rate for animals ranging from mice to steers on logarithmic axes. The points fell on a straight line with slope approximately 0.75. A cow ten thousand times larger than a mouse requires not ten thousand times more energy but roughly one thousand times more. The larger the organism, the more metabolically efficient per unit mass. The finding sat in the biological literature for six decades as a curiosity — a regularity without a theory. When Geoffrey West, working with ecologists James Brown and Brian Enquist in the mid-1990s, recognized that quarter-power scaling appeared across dozens of biological variables spanning twenty-seven orders of magnitude, Kleiber's law transformed from empirical oddity into the signature of a universal architectural principle governing all life.
In The You On AI Field Guide
The mathematical precision of Kleiber's finding is what makes it consequential. When metabolic rate is plotted against body mass for organisms ranging from