Darwin and Huxley revisited: the origin of allometry

Abstract

The relative sizes of parts of an organism frequently depend on the absolute size of the individual, a relationship that is generally described by power laws. I show here that these power laws are a consequence of the way evolution operates.

Figure 1

Allometric relations are illustrated by pictures and graphs. (a) Four neuters of the ant Pheidole instabilis reproduced from Figure 36 of Huxley's Problems of Relative Growth [1]. The size of the head is clearly relatively larger for the larger ants, an example of an allometric relationship. The line drawing between the two smallest ants shows the outlines of the four ant heads superimposed, after being scaled in the x and y directions to be the same size. (b) A double logarithmic plot of head length (circles) and head width (squares) as a function of abdomen length (arbitrary units) for the four ants in (a). (c) Idealized ants with elliptical heads illustrate an allometric relationship between heads and bodies.

Figure 2

(a) Fiddler crab. Clipart courtesy of Florida Center for Instuctional Technology . (b) Double logarithmic plot of Huxley's original data upon which his first paper [9] was based, with Uca pugnax claw weight on the ordinate and the crab weight (minus the claw weight) on the abscissa. Data reported in Table I a of [1] for sexually immature male crabs.

Figure 3

Darwin's or Galapagos finches. From Darwin's account of his voyage on HMS Beagle [23].

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