Fast evolution – the decelerating mass
Fast body mass evolution with time dilation and a downward bend trajectory
A rββ/rα-ratio around zero generates body mass evolution with a dw/dt exponent of
x = (2d-1)/2d , [3/4 in 2D, and 5/6 in 3D; Witting, 2020]
As illustrated by the blue curves in Fig. 1, the resulting trajectory is bend downward in physical time due a natural selection time that dilates as
∂ ln τ / ∂ ln w = 1/2d , [1/4 in 2D, and 1/6 in 3D]
This evolution generates the typical life history correlations that we observe across the species of today, with lifespans and other biotic periods that increase to the positive 1/4 power of mass in 2D, and the positive 1/6 power in 3D. If evolution was always following this path we would, contrary to evidence, observe 1/4 and 1/6 exponents across the entire animal kingdom.
A rββ/rα-ratio around zero is expected when resource handling evolves much faster than the selected increase in the pre-mass component of mass specific metabolism. This may be the case for the largest species in an evolutionary clade that diversifies into a multitude of empty niches; especially if resource density is increasing across the gradient of niches, or if handling efficiency is increasing as a mechanistic function of the evolutionary increase in mass.
The maximum mass for trunked mammals evolved so fast that the increase in resource handling and/or resource availability outran the evolutionary increase in metabolic pace, with a rββ/rα-ratio of 0.1 and a dw/dt-exponent of 0.79 (Fig. 2). A rββ/rα-ratio of 0.1 is also found for the maximum mass across all species of terrestrial mammals (Witting, 2020).
The natural selection of metabolism explains curvature in fossil body mass evolution
The natural selection of metabolism explains curvature in allometric scaling
- Witting, L. 2020. The natural selection of metabolism explains curvature in fossil body mass evolution. Evolutionary Ecology 47:56--75, https://dx.doi.org/10.1007/s11692--020--09493--y.