Numbers of follicles and oocytes in mammalian ovaries and their allometric relationships

The numbers of ovarian follicles present in the reserve pool of non‐growing (‘primordial’) stages at the commencement of adult life in 19 species varied allometrically with both body weight (M, in kg) and with maximum life expectation (L, in years), the mathematical expressions being 27700M0.47 and 820M1.58, respectively. These allometric relationships, which could not be accounted for by differences in reproductive behaviour patterns or ovulation rates, indicate that species differences in the size of the follicular store, perhaps accompanied by more parsimonious utilization, could be a life strategy which guarantees fecundity throughout most of the lifespan. The number of follicles in humans at menarcheal age is commensurate with body size, and follicular deficiency at menopause in mid‐life may have therefore arisen adventitiously with lifespan extension.