Articles

Morphological Diversity From Genetic Identity

by Giuseppe Semonti

Examples of highly divergent forms possessing one and the same DNA are so conspicuous and so numerous that the marvel is that they have attracted so little attention. As a symbol of morphological diversity emerging from genetic identity we can take the caterpillar and the butterfly. There is nothing in which one resembles the other:

The caterpillar is torpid; it crawls; it is usually dull-colored; its mouth has a chewing apparatus; its body is monotonously segmented, with all those hooks for feet. What we call metamorphosis is not really a change in form. Once the pupa or chrysalis stage is reached, the caterpillar starts emptying itself; its organs dissolve, and its outer covering is shed. Only certain groups of cells, called imaginal disks, remain vital. From these develop all the structures of the adult (the "imago"): antennae, stylets, proboscis, eyes, articulated legs, wings, and the fluttering lightness that warrants calling the butterfly "psyche.

Caterpillar and butterfly are widely differing forms, the one not derived from the other but both from totipotent embryo cells, some of which the caterpillar retains in its body so that they will in due course destroy it and replace it with another. The process of substituting the butterfly for the caterpillar is stimulated by adenotropic and ecdysic hormones and is repressed by a neotenic hormone. But the effects of these hormones are the simplest and most non-specific imaginable; and it is certainly not they that build the marvelous design of the butterfly on the corpse of a caterpillar. DNA may lend itself to such diverse forms, but it is not the DNA that imposes the blueprint, nor is it the hormones that do the organizing. Instead, it is one or more morphological destinies, lying in wait somewhere until they can one day reveal themselves.

Giuseppe Semonti, Why is a Fly Not a Horse?, (Seattle: Discovery Institute Press, 2005) 102, 103