Perspective: Complex Adaptations and the Evolution of Evolvability

Abstract

The problem of complex adaptations is studied in two largely disconnected research traditions: evolutionary biology and evolutionary computer science. This paper summarizes the results from both areas and compares their implications. In evolutionary computer science it was found that the Darwinian process of mutation, recombination and selection is not universally effective in improving complex systems like computer programs or chip designs. For adaptation to occur, these systems must possess "evolvability," i.e., the ability of random variations to sometimes produce improvement. It was found that evolvability critically depends on the way genetic variation maps onto phenotypic variation, an issue known as the representation problem. The genotype-phenotype map determines the variability of characters, which is the propensity to vary. Variability needs to be distinguished from variations, which are the actually realized differences between individuals. The genotype-phenotype map is the common theme underlying such varied biological phenomena as genetic canalization, developmental constraints, biological versatility, developmental dissociability, and morphological integration. For evolutionary biology the representation problem has important implications: how is it that extant species acquired a genotype-phenotype map which allows improvement by mutation and selection? Is the genotype-phenotype map able to change in evolution? What are the selective forces, if any, that shape the genotype-phenotype map? We propose that the genotype-phenotype map can evolve by two main routes: epistatic mutations, or the creation of new genes. A common result for organismic design is modularity. By modularity we mean a genotype-phenotype map in which there are few pleiotropic effects among characters serving different functions, with pleiotropic effects falling mainly among characters that are part of a single functional complex. Such a design is expected to improve evolvability by limiting the interference between the adaptation of different functions. Several population genetic models are reviewed that are intended to explain the evolutionary origin of a modular design. While our current knowledge is insufficient to assess the plausibility of these models, they form the beginning of a framework for understanding the evolution of the genotype-phenotype map.

Towards a unified science of cultural evolution

“…Evo-devo studies the mechanisms that generate the phenotype, and whether these channel, bias, or limit evolution (Brakefield 2003). Issues studied include the evolutionary origins of phenotypic novelty, how fitness improvements are made without compromising past adaptation, influences and constraints on the rate and course of evolution, and whether evolvability, evolutionary adaptability, can itself evolve (Kirschner & Gerhart 1998;Wagner & Altenberg 1996;West-Eberhard 2003). Parallel issues are key to understanding cultural evolution, so there is potential for cross-fertilisation of ideas.…”

“…Of particular relevance is the notion that modularity can favour evolvability, the capacity to generate heritable, selectable phenotypic variation (Hansen 2003;Kirschner & Gerhart 1998;Wagner & Altenberg 1996;West-Eberhard 2003). In evo-devo, "modular" describes traits that have some degree of genetic and developmental independence: they are semiautonomous units.…”

Evolvable Production Systems: Approach towards Modern Production Systems

“…Despite having some similarities HMS and EPS paradigms diverge in several points and only EPS can achieve fine granularity (Onori and Barata, 2009). According to Wagner and Altenberg, for adaptation to occur the systems must possess evolvability, which can be defined as "the genome's ability to produce adaptive variants when acted upon the genetic system" (Wagner and Altenberg, 1996) or "the ability of an organism to adapt through evolutionary changes to new or altered environments" (Bowers, 2005). It is also highlighted by Wagner and Altenberg (1996) that adaptation is possible if improvements can be made in a stepwise approach (through evolution), demanding that improvements in one part of the system should not compromise past achievements.…”

A computational model of symbiotic composition in evolutionary transitions

“…That is, if the nucleotides of a gene were somehow distributed along the chromosome then they could not maintain their integrity through sexual recombination events, they would not be likely to be copied as a unit, nor be transferred horizontally as a unit. The usefulness of modules represented in sections of chromosome depends on the correspondence of genetic linkage with epistatic linkage (Watson and Pollack, 1999c;Wagner and Altenberg, 1996)-which must not be taken for granted.…”