Fig. 1: Individual and population scaling relationships.

A Individual scaling relationships (thin gray lines) result from variation in body size due to variation in a single environmental or genetic factor, with all other size-regulatory factors held constant. However, because each individual has a single genotype and is exposed to a single combination of environmental factors, it occupies only a single point on its individual scaling relationship (white circles). The observed population scaling relationship (red line) is the scaling relationship among individuals in a population. B The distribution of individual scaling relationships determines how the population scaling relationship responds to selection (Frankino et al. 2019), and can be classified as speedometer, broomstick, or seesaw, depending on where the median point of intersection (green circle) lies relative to the bivariate mean of trait sizes (yellow circle).