Humor is a complex cognitive function which often leads to laughter. Contemporary humor theorists have begun to formulate hypotheses outlining the possible innate cognitive structures underlying humor. Humor's conspicuous presence in the behavioral repertoire of humankind invites adaptive explanations. This article explores the possible adaptive features of humor and ponders its evolutionary path through hominid history. Current humor theories and previous evolutionary ideas on humor are reviewed. In addition, scientific fields germane to the evolutionary study of humor are examined: animal models, genetics, children's humor, humor in pathological conditions, neurobiology, humor in traditional societies and cognitive archeology. Candidate selection pressures and associated evolutionary mechanisms are considered. The authors conclude that several evolutionary-related topics such as the origins of language, cognition underlying spiritual feelings, hominid group size, and primate teasing could have special relevance to the origins of humor.

Darwin's emphasis on natural selection has had a transformative influence on how biological and medical sciences are conceptualized and conducted. However, the relevance of his ideas for the understanding of psychiatric conditions is still under-appreciated. Modern understanding of disease has required appreciation of the dialectical give and take between environmental influences, life history theory imperatives, human behavioral ecology, and characteristics of adaptive processes at all levels of the individual. This has enabled a better comprehension of metabolic disturbances, cancers, auto-immune disease, inherited anemias, and vulnerability to infectious disease (1). Here we propose that a contemporary and scientifically satisfying understanding of psychiatric conditions requires adopting a similar logic of inquiry, by taking into consideration the influence of environmental contingencies and natural selection in sculpting not just brain based mechanisms and processes germane to clinical neurosciences, but also diverse characteristics of behavior.One approach to understand psychiatric disorders in an evolutionary perspective builds upon Nobel laureate Nikolaas Tinbergen's ideas, suggesting that, for a full understanding of any given phenotypic trait, one needs to detect the development and nature of its mechanisms, construed as the "proximate causes", and, in addition, its evolutionary (or phylogenetic) history and adaptive value (2). Studying the proximate mechanisms is standard in psychiatry and the clinical neurosciences, but the questions pertaining to the phylogeny of traits have largely been ignored.Admittedly, placing dysfunctional cognitive, emotional and behavioral processes in the context of possible adaptation is not straightforward at first sight. The clinical directive requires that "disorder" represent the appropriate focus. However, a "disorder" -by definition -is counter-intuitive in the context of adaptation. By adaptation we mean a genetically-mediated structural or behavioral trait, which when possessed, increased survival and reproductive success in the environment in which the trait evolved. Were psychiatry's focus be placed on "traits" (i.e., cognitive processes, emotions, and behaviors), problems which are clinically relevant could more satisfactorily be understood as distorted expression of mechanisms that in earlier environments provided answers to problems of adaptive significance, but which currently interfere in light of prevailing environmental contingencies (3). Important to the understanding of a particular phenotype is the evolutionary concept of variation. Without variation, no evolution by natural selection could take place. Mainstream psychiatry has largely ignored the fact that variation is the rule, not the exception, and this creates conceptual tensions. Psychiatry conceptualizes "disorder" as a statistical deviation from a normative statistical mean, yet handles it as a category. In other words, both "normalcy" as well as "disorder" with regard to psychological or behavi...

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Previous research has posited striatal involvement in implicit learning. However, imaging studies have not directly compared learners with non-learners. Using functional magnetic resonance imaging with 15 study participants, we used an implicit learning task previously associated with striatal recruitment. Dorsal and ventral striatum activation was observed in the eight participants who demonstrated implicit learning. Ventral striatum activations occurred to a greater extent in implicit learning versus non-implicit learning participants, and were correlated with the degree of reaction time advantage in implicit learning participants, even after controlling for general decreases in reaction time over time. These findings strengthen the specificity of the striatum in implicit learning and are suggestive of a dissociation of striatal regions relative to elements of implicit learning performance.

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The theory of evolution may be relevant to psychiatric disorders. Evolution reflects changes in genes throughout time. Thus, evolutionary forces can shape any phenotype that is genetically rooted and that possesses a long history. Schizophrenia is likely an ancient condition with a substantial genetic component. Since the 1960s, several researchers have applied evolutionary principles to the study of schizophrenia. In general, schizophrenia is either viewed as an evolutionary advantageous condition or as a disadvantageous byproduct of normal brain evolution. This paper reviews major evolutionary explanations--historical and current--that speculate on the possible origins of schizophrenia.

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