CHAPTER 3 Landscapes , Surfaces , and Morphospaces : What Are They Good For ?

Few metaphors in biology are more enduring than the idea of Adaptive Landscapes, originally proposed by Sewall Wright (1932) as a way to visually present to an audience of typically nonmathematically savvy biologists his ideas about the relative role of natural selection and genetic drift in the course of evolution. The metaphor, however, was born troubled, not the least reason for which is the fact that Wright presented different diagrams in his original paper that simply cannot refer to the same concept and are therefore hard to reconcile with each other (Pigliucci 2008). For instance, in some usages, the landscape’s nonfitness axes represent combinations of individual genotypes (which cannot sensibly be aligned on a linear axis, and accordingly were drawn by Wright as polyhedrons of increasing dimensionality). In other usages, however, the points on the diagram represent allele or genotypic frequencies, and so are actually populations, not individuals (and these can indeed be coherently represented along continuous axes). Things got even more confusing after the landscape metaphor began to play an extended role within the Modern Synthesis in evolutionary biology and was appropriated by G. G. Simpson (1944) to further his project of reconciling macroand microevolution, i.e. to reduce paleontology to population genetics (some may object to the characterization of this program as a reductive one, but if the questions raised by one discipline can be reframed within the conceptual framework of another, that is precisely what in philosophy of science is meant by reduction; see Brigandt 2008). This time the nonfitness axes of the landscape were phenotypic traits, not genetic measures at all. Even more recently, Lande and Arnold (1983) proposed a mathematical formalism aimed at estimating actual (as opposed to Simpson’s hypothetical) fitness surfaces, making use of standard multiple regression analyses. But while Simpson was talking about macroevolutionary change involving speciation, Lande and Arnold were concerned with microevolutionary analyses within individual populations of a single species. In principle, it is relatively easy to see how one can go from individual-genotype landscapes to genotypic-frequency landscapes (the two Wright versions of the metaphor). However, the (implied) further transition from either of these to phenotypes (either in the Lande–Arnold or in the Simpson version) is anything but straightforward because of the notorious complexity and non-linearity of the so called genotype–phenotype mapping function (Alberch 1991; Pigliucci 2010). This is a serious issue if—as I assume is the case—we wish to use the landscape metaphor as a unified key to an integrated treatment of genotypic and phenotypic evolution (as well as of microand macroevolution). Without such unification evolutionary biology would be left in the awkward position of having two separate theories, one about genetic change, the other about phenotypic change, and no bridge principles to connect them. One more complication has arisen in more recent years, this one concerning Wright-style fitness landscapes. Work by Gavrilets (2003; see also Chapter 17