Male CompetitionBecause male success is dependent upon access to females, not food, males compete for mates in a number of waysBy being more attractiveBy beating up the competitionNot all male-male competition is physical violenceEx: sperm competition in multi-male, multi-female social groupsOne-male multi-female groupsintense competition and infanticideMales compete with each other for access to groups of femalesTenure of resident males in groups is often very shortWhen males join groups, they often commit infanticide (kill infants)Infanticide (killing infants)Selection favors this strategy because natural selection usually acts on individuals and on relative fitnesssexually-selected male reproductive “strategyLactation inhibits female cyclingUnweaned infants death makes females available for reproduction soonerBecause male tenure is short (-2 years), infanticide enhances male’s reproductive opportunities in the context of one-male, multi-female groupsIf infanticide is a sexually-selected male reproductive strategy, then we would predict and some empirical data (observations) show:Infanticide will be linked to changes in male residence or statusMales will kill unweaned infants onlyMales won’t kill their own infantsInfanticidal males will gain reproductive benefits from their actionsPrimate Behavioral Ecology II: Evolution of CooperationOutlineDifferent types of social interactionsThe problem of altruismThe solutionsKin selectionMultilevel selectionReciprocal altruismDifferent types of social interactionsStrategies used during social interactions can incur costs or impart benefits to the fitness of those involvedGRAPH from book- cases between actor and recipient with a positive or negative fitness effect+- Selfish: improves its own fitness at the detriment of someone else++ Mutualistic: both parties cooperate to get mutual benefit-+ Altruistic: the actor does something that decreases its own benefit, to do someone else a favorHighlighted to show cooperation that we will be focusing onCalling reduces relative individual fitness of altruists if it increases chance of being eaten-- Spiteful: ill go out of my way to knock you down, when in turn they pay a cost as well, both worse offThe Problem of AltruismPresence of altruism poses an evolutionary problemAltruistic acts are costly to self and beneficial to the fitness of othersSo how can altruistic behaviors, like alarm calling, evolve by natural selection?And yet, altruism occurs in natureAlarm callsTerritorial defenseFood sharingCommunal care of youngThe Solution for AltruismHow can altruism evolve: how can the frequency of altruists ever increase?Here’s the trick:Social interactions must be nonrandom (assortative) such that altruists interact with other altruists more than with non-altruistsAltruistic acts must be “directed” at other altruists.How do primates do this?Kin selection (Hamilton 1964)Assumes that altruism is underwritten by genes.We know close relatives share genes through common descentAltruists that selectively aid kin will tend to aid those who carry same gene for altruism (creating positive assortment).Hamilton’s Rule: Altruistic acts will be favored by selection when:rb > cr: relatedness (proportion of alleles shared between altruist and recipient)the probability that 2 individual acquire the same allele due to descent from a common ancestorr value high with parents, low to non familyb: benefit to recipient (# of additional offspring resulting)c: cost to the altruist (# of fewer offspring resulting)Hamilton’s rule yields predictions about altruismAltruism is restricted to kin, as r=0 in non-kinHigher relatedness facilitates more costly altruismMultilevel selection (Wilson 1975)Altruism may evolve in a population when groups with greater frequency of altruists out-compete groups with fewer altruistsHowever, this can only occur when variation between groups is greater than variation within groupsThis is unlikely to be the case in most primates (but see humans)Reciprocal altruism (Trivers 1971)If altruists take turns giving (and receiving) benefits to (and from) each other and not cheaters, then altruism can evolveReciprocal altruism requiresFrequent opportunities to interact in different rolesAbility to keep track of help given and receivedOnly help those who provided help in pastb>cEx: grooming dyads may be examples of reciprocal altruism at work in primatesOutlineImportant components of paleoanthropologyGeologic timeGeography/continental driftPaleoclimatologyTaphonomy: How do fossils form?Dating techniques: How old are the fossils? (finishes in week 4)PaleoanthropologyThe multidisciplinary pursuit seeding to reconstruct and then explain the timing and nature of evolutionary change in the morphology and behavior of our hominin relatives.“Paleo” = oldGeologic time scale shows age in eon, era, period, epoch segmentsGeographyContinental drift: the movement of large tectonic plates on top of denser rocks beneath0-100mm per yearPaleoclimatologyClimatic conditions of the past are analyzed with oxygen isotope ratios from deep-sea coresCold periods alter the ratio of 016/018 found in the ocean, which in turn alters the ratio in foraminifera shellsShown by drilling a deep sea coreDating deep-sea coresA number of sourcesSedimentation rate estimatesVolcanic glass in cores (can be dated with K/K or K/Ar)PaleomagnetismMovement of the magnetic north pole from AD 600-1900The north pole moves/wandersEquatorial pacific core RC12-65 graph w/reversals (white part)TaphonomyThe study of how fossils and the fossil record formFossilFossilization/mineralization: the process by which organic material is replaced by minerals, creating a stone copy of the organic originalWhy are they so rare?Few conditions lead to the formation of fossils:Rapid burial in fine sedimentGentle burialCorrect chemical environment (mineral-rich water) Male Competition Because male success is dependent upon access to females, not food, males compete for mates in a number of ways- By being more attractive - By beating up the competition - Not all male-male competition is physical violenceo Ex: sperm competition in multi-male, multi-female social groups One-male multi-female groups- intense competition and infanticide- Males compete with each other for access to groups of females- Tenure of resident males in groups is often very short- When males join groups, they often commit infanticide (kill infants) Infanticide (killing