Exaptation

About: Exaptation is a research topic. Over the lifetime, 359 publications have been published within this topic receiving 18111 citations. The topic is also known as: pre-adaptation.

Exaptation; a missing term in the science of form

Abstract: Adaptation has been defined and recognized by two different criteria: historical genesis (fea- tures built by natural selection for their present role) and current utility (features now enhancing fitness no matter how they arose). Biologists have often failed to recognize the potential confusion between these different definitions because we have tended to view natural selection as so dominant among evolutionary mechanisms that historical process and current product become one. Yet if many features of organisms are non-adapted, but available for useful cooptation in descendants, then an important concept has no name in our lexicon (and unnamed ideas generally remain unconsidered): features that now enhance fitness but were not built by natural selection for their current role. We propose that such features be called exaptations and that adaptation be restricted, as Darwin suggested, to features built by selection for their current role. We present several examples of exaptation, indicating where a failure to concep- tualize such an idea limited the range of hypotheses previously available. We explore several consequences of exaptation and propose a terminological solution to the problem of preadaptation.

The Structure of Evolutionary Theory

Abstract: * *1. Defining and Revising the Structure of Evolutionary Theory * Part I: The History of Darwinian Logic and Debate *2. The Essence of Darwinism and the Basis of Modern Orthodoxy: An Exegesis of the Origin of Species *3. Seeds of Hierarchy *4. Internalism and Laws of Form: Pre-Darwinian Alternatives to Functionalism *5. The Fruitful Facets of Galton's Polyhedron: Channels and Saltations in Post-Darwinian Formalism *6. Pattern and Progress on the Geological Stage *7. The Modern Synthesis as a Limited Consensus * Part II: Towards a Revised and Expanded Evolutionary Theory *8. Species as Individuals in the Hierarchical Theory of Selection *9. Punctuated Equilibrium and the Validation of Macroevolutionary Theory *10. The Integration of Constraint and Adaptation (Structure and Function) in Ontogeny and Phylogeny: Historical Constraints and the Evolution of Development *11. The Integration of Constraint and Adaptation (Structure and Function) in Ontogeny and Phylogeny: Structural Constraints, Spandrels, and the Centrality of Exaptation in Macroevolution *12. Tiers of Time and Trials of Extrapolationism, With an Epilog on the Interaction of General Theory and Contingent History * Bibliography * Index

Adaptation, Exaptation, and Constraint: A Hormonal Perspective.

Abstract: We approach conceptual issues in evolutionary biology from an endocrinological perspective, noting that single hormones typically act on several target tissues and thereby mediate suites of correlated phenotypic traits. When several components of such a suite are beneficial, an important evolutionary question is whether all are adaptations or some are exaptations. The answer may depend on whether the traits arose in response to selection on variation in systemic levels of the hormone on variation in responsiveness of target tissues to invariant levels of the hormone. If the former, selection probably acted directly on fewer than all traits; beneficial traits arising indirectly would be exaptations. In contrast, multiple beneficial traits that arose out of independent changes in target‐tissue sensitivity to invariant hormone levels could all be adaptations. Knowledge of specific hormonal mechanisms as well as of historical selective regimes will be necessary to draw such distinctions. Endocrine c...

Genomic analysis of a key innovation in an experimental Escherichia coli population.

Abstract: Evolutionary novelties have been important in the history of life, but their origins are usually difficult to examine in detail. We previously described the evolution of a novel trait, aerobic citrate utilization (Cit 1 ), in an experimental population of Escherichia coli. Here we analyse genome sequences to investigate the history and genetic basis of this trait. At least three distinct clades coexisted for more than 10,000 generations before its emergence. The Cit 1 trait originated in one clade by a tandem duplication that captured an aerobically expressed promoter for the expression of a previously silent citrate transporter. The clades varied in their propensity to evolve this novel trait, although genotypes able to do so existed in all three clades, implying that multiple potentiating mutations arose during the population’s history. Our findings illustrate the importance of promoter capture and altered gene regulation in mediating the exaptation events that often underlie evolutionary innovations.