Behav Brain Sci. 2002 Aug;25(4):489-504; discussion 504-53.
Adaptationism--how to carry out an exaptationist program.
Andrews PW, Gangestad SW, Matthews D. (Department of Psychology, University of New Mexico, Albuquerque, NM 87131, USA.)
Adaptationism is a research strategy that seeks to identify adaptations and the specific selective forces that drove their evolution in past environments. Since the mid-1970s, paleontologist Stephen J. Gould and geneticist Richard Lewontin have been critical of adaptationism, especially as applied toward understanding human behavior and cognition. Perhaps the most prominent criticism they made was that adaptationist explanations were analogous to Rudyard Kipling's Just So Stories (outlandish explanations for questions such as how the elephant got its trunk). Since storytelling (through the generation of hypotheses and the making of inferences) is an inherent part of science, the criticism refers to the acceptance of stories without sufficient empirical evidence. In particular, Gould, Lewontin, and their colleagues argue that adaptationists often use inappropriate evidentiary standards for identifying adaptations and their functions, and that they often fail to consider alternative hypotheses to adaptation. Playing prominently in both of these criticisms are the concepts of constraint, spandrel, and exaptation. In this article we discuss the standards of evidence that could be used to identify adaptations and when and how they may be appropriately used. Moreover, building an empirical case that certain features of a trait are best explained by exaptation, spandrel, or constraint requires demonstrating that the trait's features cannot be better accounted for by adaptationist hypotheses. Thus, we argue that the testing of alternatives requires the consideration, testing, and systematic rejection of adaptationist hypotheses. Where possible, we illustrate our points with examples taken from human behavior and cognition.
example of exaptation:
- Water Bug: "Although behaviors may remain highly conserved through evolutionary time, the ecological functions they serve can undergo surprising transformations. We used phylogenetic, correlational, and experimental evidence to show how a >150-million year-old behavior, which originally evolved to facilitate migration, has been co-opted for flash flood escape in two distantly related giant water bug species (Hemiptera: Belostomatidae)" (Lytle & Smith 2004).
- "The human species is unique in its capacity to create revolutionary cultural inventions such as writing and mathematics, which dramatically enhance its native competence. From a neurobiological standpoint, such inventions are too recent for natural selection to have dedicated specific brain mechanisms to them. It has therefore been suggested that they co-opt or "recycle" evolutionarily older circuits with a related function (1), thus enriching (without necessarily replacing) their domain of use. For instance, learning to read recruits a left inferotemporal area originally engaged in object recognition, and even the seemingly arbitrary shapes of our letters may originate in a neural repertoire of junction detectors that are useful for scene recognition and available to all primates (2). In the case of mathematics, although foundational intuitions such as number sense (3) and spatial maps (4) are present in many animal species and in humans before their education, mathematical constructions vastly exceed these initial domains of inherited competence. It has been argued that analogies between number and space play a crucial role in the expansion of mathematical concepts (5). We investigated the role of brain areas for spatial coding in mental arithmetic." (Knops et al. 2009)