[Buffon and the longevity of species in the light of history].

Abstract

In 1749 Buffon proposed a general law for the longevity of species. In retrospect this law laid the foundation for modern studies of correlations between biological variables. Buffon refers to "la durée totale de la vie", the maximum lifespan, and claims that there is a systematic relationship between this variable and a measure of the growth period. It transpires that Buffon believed that by multiplying the age at the termination of the growth period by 7 one obtains the maximum lifespan. In vol III o the supplements to "Histoire Naturelle" he presents a table with, i.a., age at first reproduction and maximum lifespan for 31 Mammalian species, Furthermore, he claims that the growth period is equivalent to 2 times the age at first reproduction. From Buffon's data, one obtains a mean ratio of approximately 13 between maximum lifespan and age at first reproduction, where the expected ratio is 14 (2x7), i.e. very close to the observed ratio. Inspired by Buffon's proposition, we have investigated the same relationship in a modern dataset, comprising 564 Mammalian species. The best fitting statistical model for the relationship is not a simple multiplication, but an allometric equation: maximum lifespan = 11.47x(age at first reproduction)0.65. Taking into account the variation due to, i.a., phylogenetic constraints and adaptive divergence, Buffon's idea represents a basic biological relationship between life history characters.