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January 21 Survey Research and Other Approaches to the Study of Human Mate Preferences

January 21 Survey Research and Other Approaches to the Study of Human Mate Preferences

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SEXUAL SELECTION (continued)
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Genetic Quality Because males in many species do not provide paternal investment in offspring, generally thought that costly signals are advertising “genetic quality” Example, healthier males may have immune systems better adapted to local parasites, and females’ offspring could inherit genes for these immune responses Direct empirical evidence for signals of genetic quality?
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Genetic Quality in Peacocks 4 Peahens randomly assigned to mate with each male Eggs incubated by chickens and later in an incubator (standardized rearing conditions; control for maternal effects) Measured the mean area of each peacock’s eyespots Correlated eye-spot size to mean weight of offspring on day 84 Released 12 offspring from each male into a park and counted number of marked offspring that had survived after 24 months
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Results Petrie (1994)
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Genetic Quality In barn swallows, strong female preference for length and symmetry of male tail feathers Moller (1990) cross-fostered ½ nestlings of fathers with longer vs. shorter tails and infected nests with a common parasite Biological fathers’ tail length predicted resistance to the parasite, but foster fathers’ tail length did not Gluing longer tails onto naturally short-tailed males reduced their survivorship Biological Father Long Tails Short Tails resistance no resistance resistance no resistance Adoptive Father Long tails Short tails
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Runaway vs. Handicap Models What is Zahavi’s argument for why most exaggerated male traits are more likely to be costly signals of quality than arbitrary targets of female preferences? Other males seem to fear and defer to males with exaggerated traits: should not happen if traits are arbitrary In humans, will consider whether specific traits may be attractive because they are costly signals of health, fertility, etc.
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What are females choosing? Models of female choice evolution: Fisherian runaway selection Costly signals/fitness indicators (indirect benefits) Direct benefits Sensory bias and chase-away
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Direct Benefits 2ndary sex traits may sometimes advertise parenting ability or delivery of other benefits to female Males with brighter plumage may be better at finding food and delivering it to females/offspring (caretonids and red color dependent on diet) Male song rate may index food abundance in territory and thus direct benefits vs. genetic benefits Male size/dominance may be preferred for protection (direct benefit) vs. for good genes (primate species like chimpanzees) Healthier males may provide better paternal care to offspring Direct benefits arguments played more minor role in evolutionary biology, probably b/c males provide nothing but sperm in most species In humans, male paternal care and mate provisioning makes direct benefit hypotheses more important
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Sensory Bias and Chase-Away Male 2ndary sex traits may mimic female sensory biases
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