The concept of the theoretical morphospace

Abstract

The study of evolutionary constraint requires a metric — a map for visualizing the occupied and unoccupied evolutionary pathways that are theoretically possible. Two such maps are the often cited ‘adaptive landscape’ of genetic frequencies (from Sewall Wright) and David M. Raup's ‘morphospace’ of coiled shells. Schindel (1990, p. 270) What is a theoretical morphospace? Imagine a room whose floor is covered with beautiful glass models of sea shells. The glass sea-shell models are carefully arranged in a pattern of parallel rows on the floor, such that as you walk down one row after another, you can see the glass models change their geometries progressively from one type of sea shell to another. At the end of one row you might find a glass model that looks very much like a snail shell, but at the end of that same row the spire of the models has become so low that the glass model now looks more like a clam shell. You are walking in a theoretical morphospace (Fig. 4.1). The concept of the theoretical morphospace was first proposed by the palaeontologist David M. Raup in 1966; it is an extension of the adaptive landscape concept. Theoretical morphospaces may be defined most explicitly, if a bit tersely, as ‘ n -dimensional geometric hyperspaces produced by systematically varying the parameter values of a geometric model of form’ (McGhee, 1991, p. 87). The main difference between the adaptive landscape and the theoretical morphospace lies in their dimensions.