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Biomedical subjects

Richard Wrangham

Publications and source records attributed to Richard Wrangham.

6 recordsLinked to original sources
PubMed2006

Overconfidence in wargames: experimental evidence on expectations, aggression, gender and testosterone.

Overconfidence has long been noted by historians and political scientists as a major cause of war. However, the origins of such overconfidence, and sources of variation, remain poorly understood. Mounting empirical studies now show that mentally healthy people tend to exhibit psychological biases that encourage optimism, collectively known as 'positive illusions'. Positive illusions are thought to have been adaptive in our evolutionary past because they served to cope with adversity, harden resolve, or bluff opponents. Today, however, positive illusions may contribute to costly conflicts and wars. Testosterone has been proposed as a proximate mediator of positive illusions, given its role in promoting dominance and challenge behaviour, particularly in men. To date, no studies have attempted to link overconfidence, decisions about war, gender, and testosterone. Here we report that, in experimental wargames: (i) people are overconfident about their expectations of success; (ii) those who are more overconfident are more likely to attack; (iii) overconfidence and attacks are more pronounced among males than females; and (iv) testosterone is related to expectations of success, but not within gender, so its influence on overconfidence cannot be distinguished from any other gender specific factor. Overall, these results constitute the first empirical support of recent theoretical work linking overconfidence and war.

Adolescent↗
PubMed2005

Social cognitive evolution in captive foxes is a correlated by-product of experimental domestication.

Dogs have an unusual ability for reading human communicative gestures (e.g., pointing) in comparison to either nonhuman primates (including chimpanzees) or wolves . Although this unusual communicative ability seems to have evolved during domestication , it is unclear whether this evolution occurred as a result of direct selection for this ability, as previously hypothesized , or as a correlated by-product of selection against fear and aggression toward humans--as is the case with a number of morphological and physiological changes associated with domestication . We show here that fox kits from an experimental population selectively bred over 45 years to approach humans fearlessly and nonaggressively (i.e., experimentally domesticated) are not only as skillful as dog puppies in using human gestures but are also more skilled than fox kits from a second, control population not bred for tame behavior (critically, neither population of foxes was ever bred or tested for their ability to use human gestures) . These results suggest that sociocognitive evolution has occurred in the experimental foxes, and possibly domestic dogs, as a correlated by-product of selection on systems mediating fear and aggression, and it is likely the observed social cognitive evolution did not require direct selection for improved social cognitive ability.

Animals↗
PubMed2005

The rise of the hominids as an adaptive shift in fallback foods: plant underground storage organs (USOs) and australopith origins.

We propose that a key change in the evolution of hominids from the last common ancestor shared with chimpanzees was the substitution of plant underground storage organs (USOs) for herbaceous vegetation as fallback foods. Four kinds of evidence support this hypothesis: (1) dental and masticatory adaptations of hominids in comparison with the African apes; (2) changes in australopith dentition in the fossil record; (3) paleoecological evidence for the expansion of USO-rich habitats in the late Miocene; and (4) the co-occurrence of hominid fossils with root-eating rodents. We suggest that some of the patterning in the early hominid fossil record, such as the existence of gracile and robust australopiths, may be understood in reference to this adaptive shift in the use of fallback foods. Our hypothesis implicates fallback foods as a critical limiting factor with far-reaching evolutionary effects. This complements the more common focus on adaptations to preferred foods, such as fruit and meat, in hominid evolution.

Adaptation, Biological↗
PubMed2003

'Cooking as a biological trait'.

No human foragers have been recorded as living without cooking, and people who choose a 'raw-foodist' life-style experience low energy and impaired reproductive function. This suggests that cooking may be obligatory for humans. The possibility that cooking is obligatory is supported by calculations suggesting that a diet of raw food could not supply sufficient calories for a normal hunter-gatherer lifestyle. In particular, many plant foods are too fiber-rich when raw, while most raw meat appears too tough to allow easy chewing. If cooking is indeed obligatory for humans but not for other apes, this means that human biology must have adapted to the ingestion of cooked food (i.e. food that is tender and low in fiber) in ways that no longer allow efficient processing of raw foods. Cooking has been practiced for ample time to allow the evolution of such adaptations. Digestive adaptations have not been investigated in detail but may include small teeth, small hind-guts, large small intestines, a fast gut passage rate, and possibly reduced ability to detoxify. The adoption of cooking can also be expected to have had far-reaching effects on such aspects of human biology as life-history, social behavior, and evolutionary psychology. Since dietary adaptations are central to understanding species evolution, cooking appears to have been a key feature of the environment of human evolutionary adaptedness. Further investigation is therefore needed of the ways in which human digestive physiology is constrained by the need for food of relatively high caloric density compared to other great apes.

Animals↗
PubMed2002

Sexual mimicry in hyenas.

Genital masculinization in female spotted hyenas has been widely explained as an incidental consequence of high androgen levels. High androgen levels, in turn, were supposed to be favored because they led to adaptive aggressive behavior. Incidental androgenization is no longer a tenable hypothesis, however, because genital masculinization has been shown to proceed in the absence of androgenic steroids. Thus, an alternative hypothesis is required. The genitals of spotted hyena females are not simply masculinized, but exhibit a detailed physical resemblance to the male genitalia. In the absence of satisfactory alternative explanations, we propose that selection may have favored sexual mimicry in females because they are more likely than males to be targets of aggression from other females. Male-like camouflage could theoretically be protective in three contexts: neonate sibling aggression, infanticide by conspecific females, and interclan territoriality. Current data suggest that if sexual mimicry is important, its effects are strongest among infants.

Aggression↗