Figure 1.

The allometry of birth rates across eutherian mammals on log–log axes. In Smith–Fretwell notation, this relationship is equivalent to regressing C on R·I⁻¹ from equation (1.3). Mammals and apes scale as approximately the −¼ power of body size. The ‘other primates’ include strepsirhines and haplorhines as both clades show similar scaling. Natural-fertility human societies are the only sample here where fertility increases with body size.