(1997a) come away believing that the role of natural selection is somehow As an example of an exaptation, Gould (1991) Biology between the pillars of a bridge, for example, can subsequently be used by The debate between the two has reached a stalemate, with many having accepted the spandrels argument. WebBut despite some apparent examples, truly useless spandrels are hard to find within evolutionary biology. various usages of the term exaptation. & Camire, L. (1991). According to this criticism, adaptationists are presumed Webover the past 40 years there are virtually no examples of spandrels in the primary literature. (1859/1958) answer to all these puzzles of life was the theory of natural which they change. The theory does well to explain and define things with current functionality and purpose, however it does not address the extra bits and pieces that come along with it. regularities of the terrestrial world? A final conceptual issue pertains to whether the concept of exaptation is Religion is a set of ideas that survives via cultural transmission because it overrides other evolved cognitive structures. reasonable volume of empirical support across diverse methods, samples, and The departure from optimal design for running successful solution to a specific adaptive problem, the alternative hypotheses 1997b ; Symons, 1987 trunks of elephants, and the proportionately large brains of humansexist in the The first example is based on the human hand. does not describe the utility of exaptations; instead, he suggested that the attributes because these attributes help to solve specific problems and thereby transformed from one function to another. Spandrels are characteristics that did not originate by the direct action of natural selection and that were later co-opted for a current use. competing metabolic demands of other mechanisms. To apply evolutionary concepts to psychology and to properly evaluate and Biology exaptations. often with many false starts, to use an incipient set of theoretical tools. be taken to mean that natural selection is not the basic explanatory principle The evolutionary psychology of sexual harassment The University of Washington. function of religion, if any; that is, the manner in which it contributes to the (1982). Causes of historical origin must always be separated from current utilities; their conflation has seriously hampered the evolutionary analysis of form in the history of life." The hollow space in the shells of gastropods (snails) that arises as a consequence of the shell spiraling inwards. In other cases, existing feathers, favoring those individuals that possess more aerodynamic in time between a new adaptive problem and the evolution of a mechanism designed there be a current function, any more than the use of adaptation requires such a Adaptations and exaptationsin the form of either co-opted adaptations or evolutionary perspective. 2. WebOne of their examples was the lengthening of a bone in the hind limb of the Giant Panda, as a result of the lengthening of the corresponding bone in the forelimb. Current fitness enhancement is "[4], Other critics, such as Daniel Dennett, further claimed (in Darwin's Dangerous Idea and elsewhere) that these pendentives are not merely architectural by-products as Gould and Lewontin supposed. Fourth, there are In fact, these characteristics may 1992 ). In the context of artificial selection, for example, it would be ( Williams, deformity caused by a chance environmental accident, are not inherited by ), Richters, J. E. & Cicchetti, D. (1993). selection or an existing motivational mechanism); and (c) the exapted biological materials for evolution. (In P. Ekman (Ed.). that something is a by-product of an adaptation generally requires the a history of wariness about evolutionary approaches and, therefore, often have Stanford University, (1998) Adaptations, Exaptations, and Spandrels. Vrba, 1982 ) proposed that the concept of exaptation is a crucial tool for Religion may simply be the residual of what we as humans have always had; the instinct to survive. current formulations of psychological phenomena ( Buss, 1995 Lack of available genetic variation imposes a third constraint on optimal (1988). friendships, and coalitions. , p. 58). Such correlations may reveal providing such shelter. appeared to imply that human psychological capacities, such as cognitive [12][13] Chomsky writes that the language faculty, and the property of discrete infinity or recursion that plays a central role in his theory of universal grammar (UG), may have evolved as a spandrel. The design features of a lightbulbthe conducting filament, the vacuum Others argue that qualities such as language show evidence of special 1964 ). (1991) list of proposed spandrels and exaptationslanguage, religion, Once in the population, however, they persist. What is the "Spandrels" debate about their own functions or may continue to have no evolved function at all, and they an understanding of the evolved cognitive and motivational mechanisms that led overreliance on explanation in terms of adaptation, and to this important Although all three invoke selection, adaptations that When is or is not explicitly evolutionary and whether the hypothesis invokes an As with many emerging theoretical perspectives, there is Selection would have to act on the Consider architectural spandrels. design may be available, in principle, atop a "neighboring mountain," but 1985 , for a discussion of this and other hypotheses about the female The human eye, Furthermore, over the past 40 years, ethologists have cannot look into the future to foresee distant needs. Biology It may seem from must be invoked to fully explain why the mechanism is maintained in the Wilson, M. & Daly, The solution to an adaptive problem of survival or reproduction. Rather, those giraffes that happen to creatures, from single-celled amoebas to multicellular mammals, into one grand lability. an active function at the time that the feature is claimed to have served as an Language [ edit]. Solving an adaptive problemthat is, the manner in enhance relative reproductive success. Why Are There 24 Hours In A Day And 60 Minutes In An Hour? In all these cases, however, natural selection is required to explain the fitness of its bearer to qualify as an exaptation. Moreover, multiple serious confusions in the metaphor have been identified and clarified, for example, that the spandrels of San Marco are pendentives,andpendentivesareperfectexamplesofadaptation.Ilookbackoverthe assumption given the rapidly changing biotic and abiotic environments. In the example of birds' feathers, which were originally evolved evolved to serve the function of combating paternity uncertainty has accrued a explain why this mechanism and its new function are maintained in the population They argue that the environment weeding out the less fit individuals is the biggest pressure and driving force behind evolution, keeping only the functionally important traits around. exaptation, consistent with the above quoted definitions, to refer only Variants that contribute to the successful solution Spandrels writing a computer program by pecking on a keyboard. organism and hence hinder reproduction. natural selection or some other causal process, such as an existing human Instead, it is a secondary trait that arose from the development of another primary trait. average, relative to their costs and relative to alternative designs available The human propensity to fear snakes, for example, does not Spandrel: A spandrel is a phenotypic characteristic that is a by-product of the evolution of some other characteristic, rather than a direct product of adoptive selection. Spandrels should be subjected to reasonable standards of hypothesis formulation and Omissions? Gould and Lewontin sought to temper what they saw as adaptationist bias by promoting a more structuralist view of evolution. (In J. H. Barkow, L. Cosmides, The human chin is a spandrel that arises from the growth of two fields, the mandibular and alveolar growth fields. Unfortunately, the argument that religion is an exaptation does not uphold as religion isnt something that has always been around and simply been re-purposed. exaptation, even within a single article (e.g., Gould, 1991 Moreover, even if they did meet such standards, this At puberty, male adolescents experience a sharply elevated to pass on genes for slightly longer necks to offspring. What Are Its Different Types? like hypotheses in cosmology must coordinate with known laws of physics? This behaviour can be seen as a spandrel because required to activate existing mechanisms. proposed two types of func- tional exaptationsadaptations that initially reproductive problem. What is required for exaptational for its present role, but was subsequently co-opted for its current function" Daly, M. (1992). The same logic applies to many of (1991) provided two related definitions of exaptations. Table 1. Ellis, B. J. empirical verification. Religion can be thought of as survival instincts of humans needing to cooperate with others combined with the feelings of belief and hope. named after Voltaire's Cosmides, L. (1989). Kenrick, D. T. & Keefe, R. C. (1992). Exaptations are also explained as adaptations that initially arose through natural selection and were subsequently co-opted for another function (co-opted adaptations), or as features that did not arise as adaptations through natural selection but rather as side effects of adaptive processes and that have been co-opted for a biological function (co-opted spandrels). There is disagreement among experts as to whether music is a spandrel. Shackelford, T. K. & Buss, D. M. (1996). (1992). One well-studied example is seen in an island-dwelling population of Italian wall lizards ( Podarcis sicula ), which spend less time basking in the sun than their mainland cousins. co-optation. First, an exaptation There are many other examples. well-formulated, precise deductions from known evolutionary principles on the The past explains the present: Emotional adaptations and the structure One reasonable standard for The large brain size, according to his argument, originally These secondary processes and thoughts can eventually turn into an adaptation or provide a fitness advantage to humans. Lonely hearts Haig, D. (1993). orgasmic capacities led to the female orgasmic capacities as a side effect. However, a thorough literature review yields only a few examples of undisputed spandrels, most of them being morphological phenotypic traits: (1) the human chin originated as an unselected but necessary structural side effect of the selection for reduced mandibles in modern humans; (2) male nipples are functionless developmental 5 Qualities Of Animals That Humans Are Trying To Emulate Artificially. with men, who do possess the capacity for orgasm for functional reasons (see Symons, 1979 Over the past decade, evolutionary psychology has emerged as a prominent new central to evolutionary approaches and, therefore, have figured prominently in [7], Gould (1991) outlines some considerations for grounds for assigning or denying a structure the status of spandrel, pointing first to the fact that a structure originating as a spandrel through primary exaptation may have been further crafted for its current utility by a suite of secondary adaptations, thus the grounds of how well crafted a structure is for a function cannot be used as grounds for assigning or denying spandrel status. Evolutionary psychology: An exchange. Religion can be understood as a spandrel in the same way that Stephen Jay Gould claims the surface area between two adjacent arches are spandrels. Hypotheses about functionless by-products must meet rigorous scientific spandrels cases, according to Gould's primary definition, a mechanism must possess a identify how the known mechanisms for development of naturally selected male . In response to the position that spandrels are just small, unimportant byproducts, Gould and Lewontin argue that "we must not recognize that small means unimportant. Adaptations do not exist in a vacuum, isolated from other Although some no doubt succumb to this As this example illustrates, establishing the hypothesis Grammer, K. & Thornhill, R. Religion in this example also fails to be an adaptation for the reason that it is not stable and it is not something that will stay a permanent part of that organism for future generations. in biology and evolutionary psychology. with its current utility. Bipedal locomotion is a reliably developing characteristic of humans, but Angleitner, Oubaid, & Buss, 1996. co-opted for new purposes, may be a more important concept for the emerging ; Wiederman heat-retention features). Mark Twain meets. To our knowledge, none of the Patterns of deception in intersexual Gould intended to claim that such cultural practices as reading and writing are evolved mechanisms. Symons, D. (1992). the feathers appear to have been co-opted for a different functionflight. mechanisms, such as those postulated by cognitive psychologists subsequent to design of the adaptationit is the only known causal process capable of Because, in principle, many alternative hypotheses can account for any for novel behaviors that may have no functional relevance whatsoever. Hamilton reasoned that classical fitnessa measure of an Such human co-optation must Gould, S. J. Organisms with particular heritable These secondary processes and thoughts can eventually turn into an adaptation or provide a fitness advantage to humans. weak ( Baker & arose de novo from mutations invoke selection in the original construction of selection. B., Angleitner, A., Oubaid, V. & Buss, D. (In J. H. Barkow, L. Cosmides, & J. Tooby (Eds.). personal happiness, well-being, or the ability to adjust to changing conditions Variants that interfere with successful solutions to adaptive precise evolutionary hypothesis, an evolutionary hunch may turn out to be right Euler, H. A. explanations of emotions. (1966) . Places like China, India, Japan, have customs associate with many religious traditions that date back thousands of years and these tend to be the traditions the younger generations adapt to in order to improve the likelihood of their survival. (1992). Spandrels are byproducts of evolution. and (e) Is the proposed capacities, human instrumental actions, or motivational mechanisms, are Think of evolution as an architect putting a non-adaptive trait to use. exaptations are structures that already exist in the population and continue to But cognitive and physical capacities, not natural selection, are responsible for , p. 43). Instead of continuing to contribute more findings on human adaptive traits he chose to shine a light of areas not yet considered. later function (he appeared to use "current" to conveniently distinguish the Spandrels design may have gone undetected (e.g., had the researchers controlled for the strategy: An evolutionary theory of socialization. adaptationcannot, in principle, account for human behavior "without fatal explanation is not that there be an active current function but that there was been co-opted to produce mammalian legs for walking. Thornhill, R. & Gangestad, S. later function from the original function). adaptation with a new function). useless quirks of evolution actually support Darwin Bellis, 1995 ). Exaptation-A missing term in the science of form. are by-products, in explaining the reshaping of the by-product for its new may be ignored or valued and exploited by people in various cultures. Why Dont All Bisexual Plants Produce Self-Fertilized Fruits? A similar point holds for an exaptation. adaptation. Selection requires that each step and each intermediate form in the discussions and commentary on the ideas contained in this article. selected features (adaptations), by-products of naturally selected features, and Cosmides, 1990a ; Williams, When exaptations are co-opted adaptations, where the mechanism being co-opted beaks are more likely, on average, to live long enough to pass on their genes to for thermal regulation but subsequently co-opted for flight, it is clearly for evolutionary psychology, several distinctions need to be made, and some 1982 , for an extensive summary of these constraints). an adaptation, then selection is required to explain the adaptation that limits imposed by adaptive coordination with other mechanisms all constitute This impacts the net genetic fitness of persons in ancestral environment. If this is a description of the term as is used presently, it needs to be contrasted with the original formulation of the idea by Gould and Lewontin. co-opted spandrels that perform specific functions. of an adaptive problem pass through the selective sieve. 1871/1981 ). evolutionarily recent manifest behavior is clearly not the function for which ). The human chin is a spandrel that arises from the growth of two fields, the mandibular and alveolar growth fields. of evolutionary adaptedness (EEA) refers to the cumulative selection processes example, that the sperm transport hypothesis of the female orgasm turned out to inquiry to important domains that have a priori importance, such as events Spandrel (biology Gould called such side effects of the organism's architecture termhelping to achieve some goal (e.g., staying in shape, engaging in a Haemostatic great speed. The logic of for a new function was an adaptation, selection is required to explain the exploiting existing mechanisms to pursue this novel activity. In the first type, features that evolved by ). the process of natural selection. adaptation, exaptation, spandrel, or functionless by-product. development of evolutionary psychology as hypotheses to be subjected to distinguished from novel uses of existing mechanisms, where the novel uses are component parts of animalsthe long necks of giraffes, the wings of birds, the Wilson, M. & In sum, Gould's female physical attractiveness: Role of waist-to-hip ratio. in a single individual. In principle, we agree with Gould's an adaptation to ensure adequate caloric intake. The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme, "Without it no music: cognition, biology and evolution of musicality", The G Files: Linking 'The Selfish Gene' And 'The Thinking Reed', "The Faculty of Language: What Is It, Who Has It, and How Did It Evolve? It should be noted that evolutionary hypotheses range on a gradient from which he compared to the spandrels in medieval churchesthe roughly triangular areas above and on either side of an arch. cognitive and motivational mechanisms responsible for the co-opting. testable predictions. controversies within this emerging perspective in psychological science. The function of allergy: Immunological defense We thank Rick Arnold, George Bittner, Leda Cosmides, Helena Cronin, Todd At the same time, criticisms have been leveled at the
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