ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus110/24/17Primate Social Behavior & Mating Systems1• What is the framework for primate social behavior? Mating Systems!• Mating systems as a result of overlapping male & female strategies• Why be “social” and form groups at all?– Inclusive Fitness & Kin Selection• Effects of Social Hierarchies in primatesTopics for Today2ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus2Mating systems• Monogamy– Mono = 1, gamos = marriage, union– One male, one female• Polygyny– Poly = many, gyny = women– One male, multiple females • Polyandry– Poly = many, andry = men– Multiple males, one female• Polygynandry– Multiple males, multiple females3Figure 07.264Polygynandry:multi-maleANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus3Resource-defense polygyny5Female-defense polygyny6ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus4Why engage in same-sex competition & inter-sex mate choice?1. Which sex has the highest reproductive potential(number of offspring in a lifetime) given its mandatory parental investment?2. Which sex has the highest reproductive variance (range of numbers of offspring across the sex)?Given the above, each sex has a different strategy for maximizing its reproductive success given its different mandatory investment.7Why engage in same-sex competition & inter-sex mate choice?• Age of menarche• Age of menopause• Diet and fertility• High costs of cycling, pregnancy, lactationWhat are the Human Female Constraints on Reproductive Success (RS) (mammalian in general)8ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus5Why engage in same-sex competition & inter-sex mate choice?What are the Male Constraints?– “Where are the females?”9Why engage in same-sex competition & inter-sex mate choice?What are the Male Constraints?– “Where are the females?”• Because we are mammals with the high costs of internal gestation and lactation, male RS has a greater variance than female RS (>888 vs. 69).• Because we are mammals with the high costs of internal gestation and lactation, females are more choosy than males.10ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus611An argument used to justify male philandry (cheating)?Cornell StudyFemales are not always the Choosiest Sex12ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus7How Do Primates Form Mating Systems?Distribution of Resources (patchy)13Females map onto Resources14ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus815Females map onto Resources16Males map onto FemalesANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus9Distribution of Resources (even)17Females map onto Resources18ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus10Males map onto Females19Males map onto Females20ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus11Given twins needing paternal investment among Tamarins & Marmosets, fathers accepting polyandry is understandable.• Polygamy is not just for males! • But why are the mature siblings acting as Sibling Nannies when they could form their own family!?!?!?• Why are there multiple fathers!?!?!?21Darwinian Fitness =Direct Fitness (the individual’s fitness)+ Indirect Fitness(fitness gained through relatives)22ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus12Darwinian Fitness (including inclusive fitness)• “The sum of an individual’s reproductive success through its offspring, plus its influence on its relatives’ reproductive success, devalued in proportion to the degree of relatedness of the relatives.” • W. D. Hamilton (1964): Kin Selection23ALA #8 part 2Why did J. B. S. Haldane, one of the fathers of the Modern Synthesis, say,“I would give my life for three brothers or nine cousins!” ?24ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus13Hamilton’s Rule• Kin selection or altruism• rb > c– r = coefficient of relatedness between actor and recipients (probability that two individuals will share the same allele from a common ancestor)– b = sum of benefits to individuals impacted by behavior– c = fitness cost to individual performing behavior- r (degree of relatedness) times b (benefit) has to be greater than c (cost).Hamilton’s Rule: rb>cMore closely related individuals (higher r) can afford more costly acts of altruism.26ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus14Ground Squirrel Alarm CallingPercentage of Animals Giving Alarm Call0 10 20 30 40 50 60 70Young MalesYoung FemalesAdult MalesAdult FemalesExpectedObserved Kin Selection27The Problem with Group-Level Explanations• Altruism– Must ultimately favor the individual, not the group, to evolve– Cheaters entering the group via gene flow– Group-level explanations do not fit our understanding of evolutionary theory28ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus1529Kin Selection is a better explanation• W. D. Hamilton (1964)• Not all members of a group are equally related• Related individuals often cluster• Altruism can evolve through kin selectionKin Selection (through inclusive fitness) explainsSibling Nannies“Altruistic” alarm callsBrothers teaming up to take over a pride; brother cuckoldry30Eusociality among Naked Mole RatsANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota, Twin Cities campus16Given Inclusive Fitness, why would you want to hang around your relatives and compete with them for food & other resources?31Why Do Most Primates Form Groups?1) Resource-defense model.• Access to food: Large groups are better than smaller groups.2) Predation-defense model.• Larger groups suffer less predation than smaller groups. These two models work better with different types of primates: Resource-defense with arboreal fruit-eaters, Predation-defense with terrestrial monkeys. 32ANTH1001 Human Evolution G. Tostevin, Spring 2016University of Minnesota,
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