What does this equation mean?

Put the three numbers next to each other and the puzzle sharpens rather than resolving. A species that weans early is, on the usual mammalian logic, moving resources toward producing more offspring faster. A species that delays first reproduction by five years relative to a close comparator is, on the same logic, moving resources the other way, into growth and skill before any output. A species in which a large share of the reproductively spent population survives for decades afterward is carrying dependents — grown or not — who cannot be explained by ordinary offspring investment, because offspring investment stops paying by the time the investor can no longer reproduce. The three facts do not obviously belong to a single motive. One classic model puts a number on how much of the delay in maturity is simply growth: the allometric relationship between body weight and growth rate that Kaplan and colleagues cite from the wider mammalian literature is $\frac{dw}{dt} = A w^{0.75}$. where w is body weight and A is a taxon-specific growth constant; most mammals run at a constant of about 1, but “the mean primate value for A is about 0.4” [ 3 ] . Primates grow slowly relative to other mammals of the same size to begin with, and humans, on the same equation, grow slower still during middle childhood than even that primate baseline would predict, while gaining weight faster than juvenile chimpanzees do at ages 5 to 10 in absolute terms — 2.6 kilograms a year against 1.6 for chimpanzees over the first five years, reversing to 2.1 against 2.5 kilograms a year for chimpanzees between ages 5 and 10 [ 3 ] . Slow, uneven growth by primate standards, early weaning, late first birth, and a long tail of survivors who are done reproducing: that is the package the rest of this article is trying to explain, and it is expensive enough, in strict energetic terms, that “somebody has to be paying for it” is not a metaphor. It is the actual argument on offer three different ways.