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U of M ANTH 1001 - Lecture 4 9-12-17 Sexual Selection

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9/13/201711Today• Sexual Selection– Why do traits persist that seem detrimental to survival?29/13/20172The Peacock Problem• Darwin: “The sight of the peacock’s tail makes me sick.”• His solution: sexual selection (a type of NS)3Evolutionary Trade-off's in Sexual Selection1. Male-male Competition: – Exaggerated secondary sexual characteristics.– Sexual dimorphism.– Conflict between fertility and survival2. Female Mate Choice: – Handicaps as honest advertisements of genetic quality.49/13/20173Sexual Selection: Female Mate Choice5Sexual Selection: History of an IdeaDarwin’s View: Pre-existing female esthetic is the force selecting for exaggerated characteristics in males.Ronald Fisher’s Sexy Son Hypothesis and Runaway Sexual Selection: Females choose males with a trait that will be preferred by females, so they can have “sexy sons.”Amotz Zahavi’s Handicap Hypothesis: Males with exaggerated traits are at a disadvantage. Such a male must be VERY good to still be alive!69/13/20174Honest Advertising Hypothesis:(Building upon Zahavi)•Male “exaggerated traits” are indicators of male condition•The features that are used to indicate condition cannot be “lied” about…the indicator must be honest.•“Dishonest” indicators cannot evolve because females will be selected to ignore them (being lied to is costly).7Honest indicator example: bird coloration• Illness, parasites, starvation inevitably create byproducts.• These byproducts interfere with the production of certain pigments in birds.• “Sub-optimal” birds are duller in color than healthy birds.• We see only these colors used in the less-choosy sex’s exaggerated coloration.89/13/20175Difficulties with Darwin’s conception of evolution by Natural Selection• Did not have a working model of inheritance– Blended inheritance– Inheritance of acquired traits?• No clear account of how species formed• Genes, Alleles, DNA all unknown9Difficulties with Darwin’s conception of evolution by Natural Selection• Could only discuss evolution in terms of phenotype (one’s physical traits) and not genotype (one’s genetic make-up)• Accurate estimate of the Earth’s age was still unknown…109/13/20176Difficulties with Darwin’s conception of evolution by Natural Selection• BUT, these difficulties did not render his theories false, but make it more difficult for him to win acceptance for them• With a modern understanding of genetics and geology, Darwin’s theories of evolution (5 theories) are fully supported11Biological Evolution• It’s NOT just change over time• Lots of things change over time• Natural selection is the process of descent through modification12http://evolution.berkeley.edu/evosite9/13/20177Any


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U of M ANTH 1001 - Lecture 4 9-12-17 Sexual Selection

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