The predominance of quarter-power scaling in biology

1. Recent studies have resurrected the debate over the value for the allometric scaling exponent that relates whole-organism metabolic rate to body size. Is it 3/4 or 2/3? This question has been raised before and resolved in favour of 3/4. Like previous ones, recent claims for a value of 2/3 are based almost entirely on basal metabolic rate (BMR) in mammals. 2. Here we compile and analyse a new, larger data set for mammalian BMR. We show that interspecific variation in BMR, as well as field metabolic rates of mammals, and basal or standard metabolic rates for many other organisms, including vertebrates, invertebrates, protists and plants, all scale with exponents whose confidence intervals include 3/4 and exclude 2/3. Our analysis of maximal metabolic rate gives a slope that is greater than and confidence intervals that exclude both 3/4 and 2/3. 3. Additionally, numerous other physiological rates that are closely tied to metabolism in a wide variety of organisms, including heart and respiratory rates in mammals, scale as M^-1/4. 4. The fact that quarter-power allometric scaling is so pervasive in biology suggests that different allometric relations have a common, mechanistic origin and provides an empirical basis for theoretical models that derive these scaling exponents.