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Human Biology, Behavior, and Evolution Notes PART 12 [COMPLETE]: 90% on final!

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Boston University
CAS AN 102

Female & Male Reproductive Strategies How did sex evolve? • Population of gametes of various sizes • Disruptive selection against middle sizes, selection for small and big gametes • Initial inequality of investment: Females with large gametes, males with small gametes Female and male have different investments in reproductive successs Female primates ⁃ Produce large, limited number of egg cells ⁃ Long gestation periods ⁃ Long periods of lactation ⁃ Lengthy parental investment Male primates: ⁃ Small, numerous sperm cells ⁃ Do not gestate young ⁃ DO not nurse young ⁃ Variable parental investment Triver's Parental Investment Hypothesis • Whichever sex invests more effort and more resources in offspring is the limiting resource for the reproduction of the less investing sex and thus the object of competition • The sex investing most becomes a limiting resource for the sex investing least Reproductive success limited by ⁃ Energetic constraints on reproduction and child survivorship (food) for females ⁃ Ability to find and retain a mate for males Natural selection: Must be variation in trait, trait must be heritable, there must be differential reproductive success Reproductive success: Leaving more copies of your genes in subsequent generations than do other individuals in your population ⁃ Limited by ability to find a mate, energetic constraints on reproduction, offspring survival Naturalistic Fallacy: Just because something occurs in nature it doesn't mean it is right or justified. Can also result in things we admire: cooperation, friendship, love. Three forms of sexual selection: intra-sexual competition, inter-sexual choice, inter- sexual coercion Female reproductive strategies: • Mothers must be able to obtain as much energy as possible from food to produce viable offspring • Females seek out food and compete over it when it is limiting • Nature of the food type determines the type of relationships formed by females within groups (dominance vs no dominance hierarchies) • Dominance relationships emerge as a means to forestall outright physical aggression • Pregnancy and lactation are energetically expensive • Long pregnancies and lactations for brain growth • High investment in each offspring --> selective about who fathers their offspring • Females will enlist help of female kin or males in order to gain access to resources or protect their offspring Female strategies in chimpanzees: ▪ Females usually immigrate into a new community at adolescence ▪ Immigrants must establish a core area within their new home range ▪ Where they establish core area has a huge impact on their reproductive success ▪ Female core areas clumped into neighborhoods that vary in foraging quality ▪ Female ovarian hormones are higher in high-quality neighborhoods ▪ Females living in higher quality neighborhoods have faster reproductive rates ▪ Females living in higher quality neighborhoods have improved offspring survival ▪ Highest rates of female aggression occur between new immigrants trying to establish a core area and resident females ▪ Female-female aggression increases when new immigrants enter the community ▪
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