The Allometry of Human Fertility and Energy Consumption
In this paper we hypothesize that allometric models explain
why human fertility declines as economic prosperity and energetic consumption
increase. Allometry is the study of the relationships between an organism’s
body size, energy consumption, and biological rates. Allometric relationships
are expressed as power laws with predictable exponents that are invariant
across a wide variety of plants and animals. Recent theory builds upon decades
of empirical biological research to show that allometric constraints result
from selection on organisms to maximize both metabolic capacity and the efficiency
of internal energy transport through fractal distribution networks. Life
is constrained by these allometric relationships across levels of biological
organization including within cells, individuals and populations.
Although human ecology is unusual in many respects, humans
and human populations also face energetic constraints which are describable
in terms of allometric theory. Here we present a model relating fertility
rates to per capita energy consumption rates in contemporary human nations.
Fertility declines as energy consumption increases with a scaling exponent
of -1/3, consistent with allometric theory and the scaling of fertility in
primates and other mammals. This emergent scaling relationship can be explained
by two factors. First, the networked infrastructure that delivers energy
to consumers scales similarly to biological energy transport networks. Second,
humans act to maximize the energetic fitness of their offspring. This analysis
of human fertility offers a framework for understanding the demographic transition
to smaller family sizes, with implications for human population growth, resource
use and sustainability.
Melanie Moses
University of New Mexico
Department of Biology
melaniem@unm.edu
James H. Brown
University of New Mexico
Department of Biology