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ANT 2301 (23)
Lecture

Sexual Selection

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Department
Anthropology
Course
ANT 2301
Professor
Geoffrey Thomas
Semester
Fall

Description
ANT 2301 NOTES 09-03 Topic 2 SEXUAL SELECTION  INTRA VS INTER SELECTION  Darwin o Descent of man and selection in relation to sex (1871) o Males fight with antlers for access to females  Intra sexual selection –“male-male competition”  Females wait for victor or choose the most beautiful  Strategies o Maximize reproductive success o Males- mate w. every available female w/out getting hurt from other males o Females- choose the “most fit” mate  Sexual selection theory o Special form of nat. selection o The struggle by one sex for mating w/ other sex o Two forms:  Intrasexual selection: male-male competition for access to females  Intersexual selection: female mate choice  Happens to correlate with good genes  Greater decorations in males with polygyny  Females more decorated with monogamy  Female choice favors 3 kinds of male traits o 1) That directly increase fitness of female  Defend good territory, protect, provision o 2) Indicate good genes, offspring fitness  Peacock eyespots = >offspring survivorship o 3) nonadaptive but conscious  Frog mate call that is easiest to hear  Runaway sexual selection o Female mutant appears among pop. Of non-choosy females… o Male w. random preferred trait gets equal chance w. non-choosy +> odds w/ choosy female, so he has >RS o He passes on preferred random trait + the preference to daughters o Trait and preference spread (self-fulfilling)  Female Mate Choice o Females invest more in offspring so they have more to lose by making a bad mate choice so you expect them to be more choosy  Mate Choice Mechanisms in Primates o Active solicitation  Females in estrus will follow males around, making distinct vocalizations and facial expressions o Refusals to mate  Refuse to mate and will show aggression against courting males o Subtle signals  Sometime a female will persistently approach other males, often of a lower rank that her current partner  What traits might a female select for in a mate o Dominance rank o Unfamiliarity  Avoid harmful effects of inbreeding  Prevent infanticide o “Good genes” o Variety of mates  Group care of offspring  Difference between choice and preference o Preference is desires or propensities that an individuals possesses  Does not always result in choice o Female mate choice is an action that can be observed and measure- what the female does  May be affected by male behavior  Male behavior constrain female choice o Male-male competition  Lower males might not be allowed to get near females o Male coercion of females  Males will often use aggression to initiate and maintain coercions o Dominance and reproduction  Isn’t always what it seems- coercion (rape)  Female mate choice in chimpanzees o Females exhibit preferences for particular males o Males may affect female options o Therefore, females must try to control whether sexual interactions occur and the outcome of these interactions o Study measured whether females were effective at implementing their mate preferences  Expectations and results o Females expected to be more choosy and males more competitive during fertile periods than non fertile periods o Female success should be positively correlated with females factors such as rank and rage and negatively correlated w/ measures male rank and age o Although males were generally dominant to females the females could effectively resist male solicitations  Intrasexual selection o Commonly believed that male mating competition results in increased sexual dimorphism  Ass. w/ mating systems  Polygynous systems have unimale/multifemale groups where the male can defend the small group of females  Bigger= easier to defend females  OPERATIONAL SEX RATIO o Gros-Louis and Richards 1996: sexual dimorphism, the OSR and the intensity of male competition in polygynous primates  Consider adult sex
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