Supernormal stimulus

Abstract: Adult magpies Pica pica provide parasitic great spotted cuckoo Clamator glandarius nestlings with a diet very similar to that fed to their own chicks. In both naturally and experimentally parasitized nests, great spotted cuckoo chicks were fed at a higher rate than magpie chicks in the same nest. This preferential allocation of food by magpie parents to great spotted cuckoo chicks is consistent with the supernormal stimulus hypothesis, because this result implies that cuckoo chicks provide stronger stimuli for parental care than host chicks. Great spotted cuckoo chicks receive most of the food brought to the nest by the foster parents, because they exploit a series of stimuli which jointly (or sometimes individually) operate as a supernormal stimulus. This hypothesis predicts that if any stimulus is masked, the efficiency of the cuckoo in eliciting parental care will decrease. Here, we analyze experimentally the effects of two of these stimuli, preferential feeding of large nestlings and of nestlings with conspicuous palatal papillae. Firstly, when we experimentally introduced one medium-sized (7–9 days) cuckoo chick into an unparasitized magpie nest where the largest magpie chick was 12–15 days old, the cuckoo did not receive significantly more food than the average or the largest magpie chick. Secondly, when unparasitized nests were experimentally parasitized with a cuckoo chick that had its gape painted to mimic that of magpie chicks, the parasitic cuckoo received less food than the average magpie chick.

Abstract: Animals often respond more strongly to extreme (supernormal) stimuli, never encountered in nature, than to the natural stimulus: birds preferentially retrieve extra-large or extra-speckled eggs, for example. An analogous phenomenon in discrimination learning, the "peak shift," suggests that many instances of supernormality may reflect the action of two factors during phylogeny: (a) asymmetrical selection pressure with respect to responsiveness to the relevant stimulus continuum (e.g., size, speckledness), and (b) independent selection pressures limiting the corresponding properties of the natural stimulus.

Abstract: Supernormal Stimuli: How Primal Urges Overran Their Evolutionary Purpose Deirdre Barrett W.W. Norton and Company, 2010 There appears to be rising interest in utilizing biologybased disciplines, such as evolutionary psychology, to explain human behavior.1 There is some value in this trend. The prevailing "Standard Social Science Model" states that the human brain is a "blank slate" and that behaviors are the result of socialization and environment - entirely nongenetic in origin. The "Standard Model" predicts that the causes of psychiatric disorders and social issues, such as war and poverty, are entirely socioeconomic in origin and that solutions to these problems are to alter socioeconomic conditions. By contrast, evolutionary psychologists point out that humans, as with other animals, posses innate behaviors, the product of an interaction between genes and the environment, which developed over the course of human evolution. The evolutionary psychologists views modern human behaviors as a result of "Stone Age brains" functioning within an evolutionarily novel environment. Problems arise when humans try to address challenges that were not present in the ancestral environment. Thus, unlike the "Standard Model," there is recognition that identifying the function of genes is crucial in understanding human behavior. With increasing acceptance of genetics in the study of human behavior, it is possible that treatment of individual psychopathology will become effective and that more reasoned approaches to solving social issues will be found. The presence of instincts adapted for the ancestral, hunter-gatherer environment and modern innovations, products of human intelligence, present a paradox. Evolutionary psychologist Deirdre Barrett, Assistant Clinical Professor at Harvard Medical School, suggests that modern innovations, especially those that are exaggerated, trigger unwanted behaviors. "Supernormal stimuli" are unnatural imitations of normal cues which can "exert a stronger pull than the real thing." For example, modern foods, including fruits and vegetables, have been processed such that their taste is markedly enhanced over their natural state. The easy availability of high-calorie, fat-laden foods only partially underlies the current epidemic-levels of obesity and metabolic disorders in the U.S. Rather than entirely pin America's health problems on fast-food corporations, Barrett points out that humans instinctively sought out high calorie, fatty foods as it was a matter of survival for huntergatherers and fast-food companies are merely catering to instinct. Instead of remaining a victim to instincts, she suggests that we resist the urge to overconsume by questioning our overconsumption and to seek healthier alternatives. Thus, to overcome the products of our intelligence, we need to engage the prefrontal cortex to moderate our instincts. The prefrontal cortex also mediates intelligence, yet Barrett does not mention that those with low IQ tend to be obese and, in general, unhealthy.2 Furthermore, with the difference in IQ across racial groups there are racial differences in the prevalence in obesity, with Asians and non-Hispanic whites having lower rates than blacks and Hispanics.3 Other topics in the book follow a similar theme, the downplaying of group differences in behavior based on genetic differences. Barrett argues that supernormal stimuli can evoke intergroup conflict, seeing expensive, high-tech military hardware as an example of a supernormal stimulus, superseding primitive displays such as war dances and chestbeating. Potential adversaries may either back-down or follow their own innate tendency to defensiveness by pouring vast resources into their own supernormal military "defensive" capabilities. Surprisingly, she suggests that humans are not by nature aggressive, and that aggression is a relatively recent behavioral development resulting from overpopulation and territoriality due to the transformation from the hunter-gathering state to agriculture. …

Abstract: Reed Warblers Acrocephalus scirpaceus fostering a single nestling Cuckoo Cuculus canorus bring food to it at roughly the same rate as they do to an average-sized brood (three or four) of their own young. The food brought, mostly flies and beetles, is also similar. We conclude that the Cuckoo does not provide a supernormal stimulus. We show that Reed Warblers, given experimentally-enlarged broods of seven or eight, can substantially increase their feeding rate. This raises the question of why the young Cuckoo does not exploit this ‘spare’ feeding capacity of the Reed Warbler hosts. We offer three explanations', (i) that the increased begging necessary would attract predators, (ii) that the young Cuckoo is unable to grow faster, and (iii) that it would not be to the advantage of a young Cuckoo, dependent on its foster parents for about 5 weeks (cf. 3 weeks for Reed Warbler young), to provoke a feeding rate that the warblers could not sustain.