Exploring Geladas: Insights into Primate Behavior and Ecology
School
University of Calgary**We aren't endorsed by this school
Course
ANTH 311
Subject
Anthropology
Date
Dec 11, 2024
Pages
39
Uploaded by BailiffRainCat68
Anth 311: Primate Behaviour January 11: Class 1 Geladas and Small-scale Conservation in Ethiopia (Reading 1)- They are known as the bleeding heart baboons because of their distinctive red chest patches. The most notable baboon-related feature is their ground bases lifestyle (they are NOT true baboons of genus Papio) they are a form of their genus (theropithecus) they live in the highlands of Ethiopia, where they assemble in large herds on the high-altitude savannas and forge for roughly 50% of daylight hours. At night they sleep on steep cliff sides. They rarely climb trees. Consume a primarily graminoid-based diet(grass and sedges)- 2 well-known subspecies: Theropithecus gelada gelada and Theropithecus gelada obscurus, both live in the Rift Valley of Ethiopia - Ecological specialists. Studies found that they spend roughly 90% of feeding time on above-ground graminoids during the wet season- One male with 2-10 females with sole mating access to these females. Females stay in their natal groups. Juvenile males disperse around the age of 6 and live in all-male units for several years. As polygynmous pirates, geladas experience high levels of male-male competition resulting in pronounced sexual dimorphism (male 19kg female 11kg) In such a social system infanticide risk is high for females. Females have been observed to spontaneously terminate their pregnancies following the arrival of a new harem male.- Live in multi-level societies that exhibit fission-fusion dynamics in a hierarchically nested social organization. Herds can reach up to 1200 individuals January 16th: Class 3Humans as PrimatesAnthropology: the study of humanity 1. Socio-cultural 2. Linguistics3. Archaeology4. Physical(biological)Why study primates in anthropology?- Primates are our closest living relatives- Like other primates, humans are highly social - Some traits that we conceive as human are inherited from our NHP(nonhuman primate) ancestors
5 types of primates*(65 million years or earlier) - Lemurs and lorises(most primitive traits)(strepsirrhines-curved nose/wet nose)- Tarsiers- New world monkeys- Old world monkeys - Apes (Haplorhines-simple nose)What is a primate?- No single characteristic1. Emphasis on vision more than smell 2. Emphasis on manual dexterity a. Opposable thumbs b. Nails instead of claws 3. Generalized dentition 4. Big brains for their body mass 5. Long life spans and slow growth 6. Social relationships 685 species and subspecies of primates - Mostly tropical Humans as Primates1735- Linnaeus introduces the binomial system of taxonomy in his Systema Naturae(the first to call humans primates)- Chimpanzees and Bonobo are more closely related to each other than gorillas because of “Pan”- The last common ancestor LCA of chimpanzees, bonobos, and humans lived 6-9 million years ago and was- Black haired- Knuckle walking- Chimp sized- Eating fruits/leaves - Ape size brainRelevance of nonhuman primates in human evolutionary biology Homoplastic traits(convergent)- Traits that appeared in the last species AFTER the last common ancestor Homologous traits(primitive)- Traits that were probably shared with the last common ancestor - EX: 5 fingers/same as other primates/ancestors Homoplasy vs HomologyBaboons and Chimpanzees are used as “referential models”- Used to understand early human behavior- Early studies on baboons find that many characteristics affect behavior
Louis Leakey and 3 pioneering primatologists- Jane Goodall (chimps)- Dian Fossey (gorillas)- Birute Galdika (orangutans)January 18th: Class 4Earths history - If compared to a calendar year- January first: 4.6 billion years ago - Dec 14-26: Jurassic and Cretaceous periods, the time of the dinosaurs - Dec 31, 11:37 pm: Modern H. Sapiens appear- Dec 31, 11:59 pm: Industrial revolutionAdaptive radiation- Refers to the evolutionary process by which a species diversifies to occupy different ecological niches- Leads to speciation and organisms become differentiated from one another and their common ancestor Characteristics of primates- No single feature - Primates are primarily tropical, tree-dwelling (arboreal) mammals with excellent visual systems, grasping extremities, big brains, and slow life histories- Posses combination of ancestral and derived traits - Locomotion- how they travel/walk- Knucklewalking- Suspensory - Terrestrial quadrupedalism - Vertical leaping/clinging- Generalized limb structure(pentadactyly)- Fingerprints- Grasping extremities(prehensility)- Nails rather than claws(callitrichids(tamarins and marmosets) have re-evolved claws)- Large brains relative to body size compared to other mammals - Big neocortex- Responsible for cognitive abilities such as reasoning - Link between brain size, sociality, and learning - In primates, the neocortex makes up 50-80% of the brain's total volume- Generalized dental pattern- Related to omnivory - Heterodont: having different tooth shapes (homodont-same tooth shapes)- 32-36 teeth - BUT some specializations
- Primate Origins - Plesiadiforms - “Archaic” primates - Paleocene (65mya)- North America, Europe, and Asia- Most have nails, not claws The Eocene(56-34 Ma)Primate Origins- Arboreal hypothesis - Primate trait used in a complex 3D environment - Visual predation hypothesis - Primate traits useful for predation - Angiosperm co-evolution hypothesis- Primate traits useful for grasping fruits and flowers; mutually beneficial relationship Strepsirrhines- Bushbabies- Lorises and pottos - Lemurs(only found in madagascar)- Long muzzle with moist nose(rhinarium)- Tapetum lucidum(causes eye shine)- Orbits not fully enclosed in bone - Two part mandible - toilet/grooming claw on second toe - Toothcomb in lower jaw - Behavioral Characteristics:- Lemurs- Nocturnal or diurnal - Solitary and gregarious - Arboreal and terrestrial - Mainly frugivorous - Laorises and Galagos - Nocturnal - Often solitary - Arboreal - Feed on gum, sap, nectar and insects
Haplorhines = anthropoids(monkeys and apes)+ tarsiers - Tarsiers (south asia)- New World Monkeys (central america, south america)- Old wold monkeys (africa and asia)- Apes - Diverged from streps -63mya- Larger brains relative to body size - Orbits fully enclosed by bone - Dry noses- Mostly diurnal - No vitamin C production(streps produce this)Tarsiers- Nocturnal - Arboreal - No tapetum - Nostrils separated from mouth by dry upper lip- Orbit encased in bon e- Eats insects and small vertabrates- Some solitary pair-bonded, some groups Anthropoidea - Monkeys apes and humans Features:- Reduced muzzle - Dry nsoe - Nails on all digits - Complete bony eye orbit - Fused lower jaw
Platyrrhines(new world monkeys)- Some have a prehensile tail - 3 premolars- All arboreal Behavioral Characteristics - All diurnal except for Aouts(owl monkey)- Arboreal - Social systems and diet vary between species - Smaller-bodied New World monkeys(marmosets and tamarins)= Callitrichidae- Some pair-bonded, some polyandrous - Twins - Eat gum- Larger bodies New world monkeys - Multimale- multfemale or one male units - Frugivors and folivores CatarrhinesOld world monkeys+ apes and humans(hominoids)- 2 premolars - All diurnal - Aboreal or terrestrial Cercopithecoidea- OWM- Two major groups 1. Colobines - Leaf-eating monkeys - Special stomach to aid in the digestion of low-quality food - Reduced or absent thumbs - Mostly arboreal and mostly folivores 2. Cercopithecines- Check pouches(food storage)- Diet and social systems vary - Arboral and terrestrial - Female philopatry and strong FF bonds Hominoidea - All apes(including humans)- Gibbons and siamangs - Oragnutagns - Gorillas - Chimpanzees and bonobos - Humans - Gregarious (except orangutangs)- Mostly frugivores except gorillas)- Arboreal and terrestrial - Exhibit diversity of social systems
January 23: Class 5 Natural SelectionTwo Observations:1. Animals are extremely well adapted to their environment 2. Many of the adaptations are extremely complex Evolution: small changes over long periods of time - Phenotypic: controlled by genes - GenotypeLamarck theory of the inheritance of acquired characteristics (WRONG)- Things happen to you over the course of your life that change and get passed on 1. Evolution as a historical phenomenon a. What happened over time(Pre-Darwininan idea)2. Natural selectiona. How it happened 3. Evolution VIA natural selection a. Charles Darwin/Alfred Russell Wallace Darwin and Wallace - Darwin had it “more right” than Wallace- Took 22 years to write his book based on his observations - Wallace would collect specimens Natural Selection - The process by which traits become more or less common in a population - One mechanism that causes evolution - 4 conditions 1. Competition 2. Variation 3. Reproduction 4. InheritanceCompetition - Over reproduction is always a threat(every species)- Lead to extreme competitions - Limited resources - Food - Shelter - Mates - Not everyone can survive and reproduce
Example: FINCH(Darwin)Diet:- Cacutm fruit - Flowers - SeedsDepending on what food is being eaten- the beak shape changes 1977-78- Drought on daphne major(island)- The seeds got harder(change in the environment)- Medium ground finch died because they are not able to handle the hard seeds due to ecological change - Birds that had deeper bekas had better survival Adaptation: a feature shaped by natural selection, promoting survival and reproduction Fitness: the relative ability of an organism to survive and transmit its genes to the next generation - Direct fitness: # of your genome copies you directly pass to the next generation - Indirect fitness: # of your genome copies passed indirectly to the next generation via kin - Inclusive fitness: # of your genome copies passed in total to the next generation(Direct + Indirect Fitness)Hamiltons Rule - If you are going to help someone you should get something in return based on how closely related you are- “I would lay down my life for 2 brothers OR 8 cousins”- Share a proportion of genes with relatives- More likely to help close kin What is evolution?- The non-random survival of randomly variating replicators - The sum of changes in allele frequencies in population over time - Descent with modification Typological thinking - Ideal types/essences- Reality = deviation from ideal - No variation Evolutionary thinking - Population thinking - Variation with species is the essence - Individuals = samples of populations - Probabilities, not certainties - Phylogenetic (tree thinking)- Variation between species - Can examine when traits arose
Misconceptions:- MASSIVE shifts in thinking: Everything is related and every living thing is equally “evolved”- Individuals don't develop- populations evolve Non-Adaptive Traits 1. Mutations Genetic drift - Random fluctuations in allele frequencies - Population bottlenecks - Contraction of population size due to environmental event/ecological factor - reduced genetic diversity - Founder effect - Founding of new population by non-representative sample 2. Incident by-productPhenotype: a description of your physical traits Genotype: your heritable genetic identity Behavior- How animals interact with the environment and each other - An animal response to a stimulus carried out by the Musco-skeletal system - Pleiotropy: one gene affecting several phenotypic traitsBehavioral Ecology - Evolutionary theory applied to behavior - Same conditions apply as with natural selection- Competition - Variation - Reproduction - Inheritance Sociobiology/behavioral ecology - Applying evolutionary principles, specifically natural selection, to behavior - Trying to understand how behavior might be naturally selected/adapted/evolvedTinbergens 4 questions and levels of analysis 1. Adaptive value (function)2. Evolutionary History (phylogeny)3. Causation (mechanism)4. Development (ontogeny)
January 25: Class 6 Sexual Selection Phenotypic gambit: ignore genetics and focus on the fitness of phenotypesEstrus: the period around the time of ovulation where the female can conceive (can advertise the timing of their ovulation)Ex: baboons sexual swelling. New world monkeys don’t have advertised ovulationCurrency used to measure ‘success’ in evolutionary terms = the number of offspring an individual produces Sexual selection- Darwin - Addition to natural selection needed to explain differences between the sexes- Intrasexual selection = competition for mates- Intersexual selection = choice of mates Bateman principle - Males benefit predictably by mating multiple females - Females need only one mating partner- Females as the “ecological sex”- Males are the “mate getting sex”- Why are males bigger- Better fighters- Favored in female - Have more offspring Two types of mating system1. Polygynous- many females per male 2. Monogamous- one female per male Sex ratio changes based on the operational sex ration which means how many animals are sexually active and sexually receptive - More competing males per sexually active female = relatively larger males Scramble competition - High rate of sperm production - High sperm quality - High readiness to mate Infanticide4-step mamalian socioecological model 1. Environmental risks and resources 2. Female ecological strategien3. Male mating strategiesa. Male coercion b. Female counter-strategies
- Infanticide first studied in colbine monkeys in Asia- one male multiple females- Aggression directed at a females infant that makes her more likely to mate with the aggressor or liekly to mate with other males at a cost to the female- When a male kills an infant the female mates with the male that kills the baby and creates a rapid inter-birth interval - Not inherently infanticidle(only very specific situations)Geladas- Always fighting - Estrus located on the females chest- Sitting pads - Bruce effect(termination of pregancy before the baby is born)- Male takeover of hare in geladas- Hormonal evidence for pregnancy termination in gelads following male takeover(through collecting fecal matter)- Traumatic events for the femalesJanuary 30: Class 7 Chimpanzees and BonobosMonophyletic = group contains a common ancestor and all of its descendants Paraphyletic = group does not contain all descendants of a common ancestor Chimpanzees- Moderate sexual dimorphism - Femlaes 40kg- Males 50kg - Lowlnad forest and woodland - Pan troglodytes- Diet- Ripe fruit - Young leaves- Pith, flowers- Insects, meat- Preferred foods- eaten in proportion to availability, high quality - Fallback foods- always available, eaten when preferred foods scarce - Spend over 50% of their day time hours chewing - 30-200 indiviiduas in a community - A typical community - Most females anestrous(not in estrous)- All community members are never together at one time Bonobos- Once known as “pygmy chimpanzee”- but actually, same size as chimpanzees- More juvenile-like behavior - More play, less aggression - Pan paniscus- “Parties” - Diet- More leaves compared to chimpanzees
- Fission-fusion - Also assemble in parties February 1: Class 8 BaboonsTest: 80 multiple choiceOld world monkeys- CerceopithecoideaOmnivorous Complex social organizaiton Cercopithecines- Morphological characteristics - Cheek pouches(food storage)- Behavioral characteristics - Both arboreal and terrestrial - Female philopatry which leads to strong FF bondsMandrills(forrest baboons)- Poorly known primate - Fruit motivates omnivore - Female hordes w/male influxes during breeding season - Big group of females and males are off living in solitary besides breeding season - Male coloration testosterone-dependent and reliably correlated with male rank Drills- Fruit omnivore - MM-MF or OMU possibly-tiered super groups Theropithecus gelada(not baboons)- Ethiopia - Grass eater- Female philopatric - Multi-tier social structure, OMU reproductive units - Female social within matrilines- Genus: papio- Tropical grasslands- Chacma baboon- infanticide really high Savannah baboon social organziation - Stable troops - >10 females- >5 males - Large, diurnal terrestrial quadrauped - Easily observe- Best studied primate - Generalist diet - Social structure - F-F: kinship(relatedness), alliances(female- - bonded)- F-M: friendships + consortships
- M-M: dominance, since coalitions- Female philopatry - Females breed in natal groups - Males disperse in adolescence or early adulthood - Importance of kin- Females form kin-clusters - Spatial association: grooming/how close to eachother - Domiancne rank among females - Younger daughters have advantage/higher ranking when about a reproductive age- slotted into dominance rank-one below the mother but above the older sisters- because of reproducutive value(more ability to reproduce)- Stable ranks (all FF in one matriline outranks FF of another)- High ranking female baboons tend to eat better and have higher reproductive success- Coalitionary support is kin bias - Female-male relationships - Consortships + friendships - Always paying close attention to the sexual swelling - One female, one male - Typically a few hours at at time - Consortships occur for a few days around ovulation - Dominant male tends to take over at peak fertility - Friendships - Males and females spenting time together grooming eachother outside of the ovulation period - Females have 1-2 male friends - Males have 0-8 female friends - Freidnship benefits - To the female - Protection by male and babysitting by male- tend to be intolerant of infants except friends - To the male - Paternity: increased present and future probability of paternity or maybe they have already mated and hes caring for HIS baby- Agonistic buffers: Friends infants are used as buffers(no one will attack you that bad if you have a baby)- Male-male relationships - New male immigrants have highest ranking(young/pumped with testosterone and the best fighters)- Frequent coalition partners - Tend to occur betwee older and mid ranking individuals
Hamadryas baboons- Omnivore, very arid habitat (low resource density)- Neither sex philopatric but some males stay in natal clan or band - Multi-tier social structure, OMU reproductive untis - Females social mostly with unit male - High infanticide risk - Groups of females widely dispersed - Males are huge and mean to make sure that females dont stray away at all
AFTER EXAM 1February 8: Class 10 Primate diets and socioecology “Diet is the single most important parameter underlying behavioral and ecological differences among living primates”Diet Requirements:- Carbohydrates- Amino acids(protein)- Fats and oils - Vitamins, minerals - Water Avoid toxins:- Concentrated in adult leaves - Examples: caffeine, tannins, alkaloids2 theories on food as a selective pressure 1. Satisfy nutritional requirements- Relevant concepts for human society, zoos- Energy: -> maintain condition, immune system - Micronutrients: -> dietary imbalance 2. Maximize nutritional gain - Predicted by optimal foraging theory - Animals limited by food supply - Energy: -> maximize net energy gain -> maximize fitness Optimal foraging - Foraging behavior based on intrinsic properties of potential foods:- Nutritional quality - How much time/energy to fin and harvest - What item to include in the diet? What kinds of patches to occupy? How long to stay?- Maximize- Amount of food - Quality of food - Minimize- travel/search time - Processing - Digestion - Competition Captivity vs wild - More food=more babies - Provisioned baboons = grow faster and reach sexual maturity earlier 4 factors determine how much food is required per primate1. Basal metabolic rate2. Active metabolism
3. Growth rate4. Reproductive effort (17-30% extra costs in lactating females)Wild fruits are not as rewarding as bananas(nature-perfect food/infinite/highly digestible)- Low pulp to seed ration - Pulp often dy and strong tasting Digestive adaptations to frugivory - Large, broad incisors - Low cusped, relatively flat molars - Large (but relatively unspecialized digestive system)Leaves- Foliage (leaves and stems)- Main fallback for frugivorous primates - Preferred food for some (esp colbines) Adapted to deter folivory - Rich in protein, but tough and often toxic Folivores- Large body size - Small incisors - Sharp shearing crests on molars- Enlarged, well-developed digestive systems Fibre protects foliage by reducing digestibility, making chewing difficult - Humans eat much less fibre(50-10%) than apes and many monkeys(30-35%)Seeds - Rich in lipids and protein - Protected by shells and or toxins - Specialisation needed to crack nuts - Thick enamelled molars in species that open nuts (durophagous foods)- Saki pithecia(long canines)Insects - Rich in lipids, protein, easy to digest bu hard to catch- Small primates, large canines, sharp cusps - Tarsier- the most insectivorous of the primates(NO plant food)pointy molars for slicing animal prey - Aye-aye: huge incisors for gnawing wood to get to larvae under the bark Chimpanzee diet- Preferred food is ripe fruits: eaten in proportion to availability - Fallback foods: eaten in(negative) proportion to preferred foods Liem’s paradox- Species often prefer not to eat the foods to which they are specifically adapted Niche differentiation is NOT OBVIOUS when food is abundant Chimps and Gorillas- Live sympatrically- in the same habitat- Same fav food(fruit)
- Can eat similar amounts of fruit - Many of the species of fruits in their diets are the same Niche differentiation IS OBVIOUS when preferred food is scarce- For example when the fruit supply is scarce chimps seek ripe fruit while gorillas seek leaves and stems- Feeding adaptations tend to be for fallback foods(diet when food is scarce)Solution to Liem’s paradox - Foods to which species are adapted are fallback foods - Preferred foods are easy to eat(ripe fruit) they tend not to demand special adaptations - When preferred resources are available, they are eaten- Feeding adaptations are mostly designed for the diet when food is scarce because that is when individual variation in feeding success matters most2 types of feeding competition - Scramble competition: occurs when increasing the group size results in less food for every individual - Contest competition: dominants get access to food over subordinates - Can be within-group or between group or both - Type and degree of competition experienced by animals is affected by the abundance, distribution and quality of the food Optimal group sizes- Hypothesis: natural selection should balance the costs and benefits of group-living to result in optimal group sizes- Intermediate sizes should be associated with better individual feeding success-> higher RS, lower stress levels, etc - These patterns are confirmed in some species but not in others February 13: Class 11- Multi-level sociality (REVIEW LECTURE)Multilevel societies - Most complex social systems in mammals - Social systems with multiple distinct social levels are nested within each other (each level includes the ones below it)- Humans live in multilevel societies - Highly integrated social networks- Immediate family (kids/spouse) - Related Family(siblings/parents)- Extended family (cousins/aunts/uncles)- Friends and family Importance of studying multilevel societies- Fundamental to understanding the evolution of human sociality - Insight into the origins also help us understand the adaptive functions of social complexity At least 7 primate species with multilevel sociality - Proboscis monkey - Gelada - Douc langur
- Hamadryas baboon - Snub Nosed monkey Not just in primates and humans (elephants, killer whales, zebras, sperm whales) Can vary in:- The number of social levels - The names given to the social levels DEFINITION:- Social systems of a minimum of 2 stable and consistent levels between the individuals and the population - Core unit(one male unit) and upper-level(band- one male with multiple reproductive females + their offspring) (BOTH ARE MANDATORY)- Each level contains the next CORE: - Highly cohesive and stable - Interact more frequently within their own unit than between unit( stay in regular or permanent proximity)- Usually polygynous(OMU)- Follower males(don't desire any offspring)- Most socially cohesive INTERMEDIATE LEVEL: - Closely associated core units - Interact more with units in the same clan - Not mandatory UPPER LEVEL- Multiple core units - Stable enough to be recognized - Membership in an upper level can be consistent or not(may separate)APEX LEVEL- Temporary aggregation of upper levels at sleeping sites or foraging sites - Distinctively larger - Not mandatory - Bands will come together and sleep nearby for safety How do we know that they are true organisation levels?- Quantifying social levels Fission-Fusion Dynamics - Cleave and coalesce to form subunits in response to socio ecological factors - Food availability, predation, mating - Subgroups vary in size and composition - Not a type of social system Why split? EX: HAMADRYAS BABOONS- Operate different functions at different social levels - OMU- access to reproductive partners - Clan- male-male relationships - Band- protection and resource defence
- Troop- predator protection at sleeping cliffsEvolution of Multilevel societies- Gelada and Hamadryas baboons- Originally large multi-male multi-female groups - Large group sizes due to localised resource - High aggression and harassment by unfamiliar individuals - Split into stable OMUs- Snub-nosed monkeys- Independent OMUs merged due to the persistent threat of infanticide from bachelor monkeys Social structure of core units- Geladas- Female philopatric - Core units shaped by kin bonds among closely related females- Female-female bonds - Hamadryas baboons - Male philopatric - Pair bonds between the leader male and his females provide core unit stability - Male-female bonds - Female dispersal limited to band(females are highly related within their bands)- Females are more closely related maternally within OMUs - Leader and follower males are more closest related maternally then expected - Kin selection among females is likely an organizing principle Consequences of MLs- Reproductive units and bachelor males live in close proximity - A high density of competitors - Promoted evolution of signals of male quality - Sexually dimorphic traits are more pronounced in MLS compared to other societies (Red Chest on Gelada)
Class 12: Social BondsWhy do primates form social bonds/how does it affect well-being?Example: Brains of polar explorers shrunk after 14 months of solitude- prolonged social isolation associated with reduced cognitive function- No true example of solitary humans - Innately social - Social relationships make humans healthierBonds:Female-Female bonds: - Defence against males - Competition with other females - Younger daughters have a higher rank - Female bonobos form coalitions more often than males- Coalitions are all against males. females always win - Olive baboons: agonistic relationships among females have few reversals Cercopithecine monkeys - Matrillenail hierarchies against other matrillenials- Close kin are allies against more distant kin - Infants of mothers that are more social survive longer - Buffer - Benign environment for infant - Access to resources, lower rate of harassment, mother less stressed- Okavango baboons- Longevity = more reproductive successMale-male bonds:- Much rarer in males because of competition - Restricted primarily to species in which males are usually the philopatric sex(chimps)- Some groups have no male-male bonds - Polyadic aggression: 2 or more individuals acting together in aggression against others - Coalition: an interaction. Partner might not be a long term ally- Alliance: a relationship. Partner is a long term ally (has social bond)Dominance rank:- In chimpanzees males often display to assert dominance . to test whether others express subordinacy - Hair erect, stand bipedal making subordinates look small, give submissive grunts or screams
- male/female conflict of interest: - Female aim: mate with many males(paternity confusion)- Male aim: mate guarding(paternity certainty)- Maintain close proximity to female - chase/attack males - attack/intimidate female - Some males will let other males mate with his female to gain/maintain social hierarchy Assamese Macaques- Female philopatric - Male dispersal but nonkin males form close social bonds - Males in many species seem unable to set aside their competitive differences to form bonds that could, over the long term, be of mutual benefit.Female-male bonds - Sex biassed dispersal does not allow kinship bonds to form between the sexes - Male RS is increased by limiting association with Females after fertilization Benefits to male: - Future matings - Increased social support Benefits to Females: - Help with offspring - Increased access to resources - Protection against predation - Protection against aggression and infanticide Male-Female friendships: - Hanging out outside of the estrous time - Defined by a break in a frequency distribution of proximity scores Baboons - Against infanticide and the consequences of female aggression in baboons - Paternal care (males taking care of their babies)- Access to future mating partnersChimpanzees- No friendships between males and females in chimpanzees IMPORTANT- What leads to all of the relationships - Aid in longevity = higher reproductive success
Class 13: Dominance and HormonesBiological Sampling:- DNA-feces/hair/corpses- Parasite load-counting parasites in poop- Physiological correlates of behaviour-feces/urine(catch urine out of the trees)Hormones- Chemical messengers produced by the endocrine system - Endocrine gland: release hormones inside the body (into blood)- 2 effects of hormones - Organizational (Longterm)- Irreversible effects at birth - Occur during development - Activational (short term)- Temporary effects- Mostly in mature individuals - Act in body and brain2 types of hormones - Steroid hormones (sex hormone)- Circulate in blood- Found in saliva- measurable - Excreted in urine and feces- measurable - Glucocorticoids (cortisol-stress hormone)- Peptide hormones(c-peptide/insulin)TEST Q- Relatively longer 4D (lower 2D:4D ratio) indicates higher prenatal androgen exposure PAEFood and Female Reproductive SuccessAssumption- female RS is limited by access to food - Some measures of RS:- Earlier age of first reproduction - Shorter inter-birth intervals - Higher infant survival rates - Better survival during mortality crisisEnergetic Condition - Energy intake and output are difficult to measure - Insulin regulates glucose use(for energy or storage)- C-peptide shows how much insulin is produced by the pancreas - The amount of c-peptide tells us how much insulin is being produced by the pancreas- Wild animals are more limited to food access so they should have lower c-peptide than animals in captivity
Cortisol- A measure of both energetic and social stress- Higher in lower-ranking females - Higher-ranked females are not energetically stressed- Energetics of male dominance rank - Higher-ranking male chimps- Lower c-peptide/higher cortisol - Do not travel further than lower-ranking males - Are more aggressive than lower-ranking males - Aggression is energetically expensive - More charging and chasing - Higher levels of c-peptide Baboon study- Lower ranking animals have more stress hormones-except alpha males- In both stable and unstable hierarchies - Likely associated with increased energy expenditure from constantly fighting Male Dominance and Testosterone - Male RS is limited by access to females - In multi-male groups- males tend to compete - Higher-ranking males have significantly higher levels of testosterone Challenge Hypothesis - If maintaining high testosterone is costly, then male testosterone should increase when it's more advantageous(when reproductive opportunities are present) and peak when you're challenged - Prediction 1: Males should show increased testosterone production during the peri-ovulatory period or parous females(have given birth before)(correct)- Prediction 2: A rise in T is related to aggression not just copulation(correct)Female Dominance- Higher-ranking females also exhibit higher T- Higher rate of aggression - Females compete for statusFun Fact- vervet monkeys had blue scrota-brighter the blue the higher the rank
Class 14: Intergroup AggressionAre humans innately peaceful or violent?- Capacity for warfare is a human universal/unlikely to be simply a cultural artifact In-group vs out-group psychology- Likely shaped by a history of intergroup conflict Analyzing group-level processes- Must start with an individual level approach - What are the individual incentives to participate in between-group aggression - How is this balanced with intra-group competitive - Collective action problem - What are groups fighting over?- Resources (defend access to food)- Mates(done by males)- Intergroup dominance status(ability to win battles)Female defence hypothesis - Males are primarily concerned with defending females in IG conflicts - Male aggression should increase when sexually receptive females are present/higher ranking males should be more active in defenceResource defence hypothesis - Males can benefit by defending territories that are important to female RS- Defending access to food(territory) is indicated by home-field advantage Imbalance of power hypothesis - Troop living species: killing is rare- Little contact aggression in intergroup interactions - Few coalitionary attacks - One explanation is that the groups are similar in size - Lethal raiding: found in species with “parties”Why do some primates form coalitions to kill?*****1. Fission fusion social organzation (ecology)2. Subgroups vary in size, so large parties may meet lone members of a neighbouring group3. Asymmetrical distribution of the dominant party can afford the cost of aggression**** 1. Ecology 2. Fission-fusion grouping 3. Potential imbalances of power4. Low-cost lethal aggression 5. Increased inter-group dominance 6. Increased access to resources + mates
Prediction 1: power asymmetry between opponents provokes attacks Prediction 2: Power symmetry suppresses attack - Prolonged interactions - Mutual call, display fake attack, charge, little/no contact - Ends in one or both parties withdrawing - No death Prediction 3: victims of aggression tend to be male Prediction 4: Inter-group dominance = resources - More territory = higher body mass/bigger parties/ shorter interbirth intervalChimpanzee intergroup encounters- Resource defense polygyny- Male territoriality centres on a resource needed for breeding success- Females benefit from access to feeding sites- Males benefit from access to those females - Females don't participate in conflict directly, but: - They do vocalize before encounters to make groups seem larger/encourage attacking malesBonobos - Pass food around to other bonobos Implications for Humans - Parallels between chimpanzees and small-scale human societies(below military horizon)- Conflict over resources - Conflict precipitated by imbalances of power: avoid battles if possible - Small-scale warfare isn't necessarily very deadly - Risk of intergroup interns may have been very important in human evolution, even if mass mortality events were not observed- Above military horizon - very deadly Class 15: Life History and DevelopmentLife history - Patterns of growth, development, reproduction, and mortality - Natural selection alters timing of these events to maximize reproductive success - Pervasive tradeoffs(fixed pools of energy)Key trade-offs in life history - Number vs quality of offspring - Current vs future reproductive function - Age versus size at maturity - Resources (Growth, maintenance, reproduction)- Compared to most mammals, primates mature more slowly Juvenile- Weaned
- Sexually immature - Independent locomotion - Able to survive if caregiver dies - Not full-sized Basic Life history model(Charnow model)- Assume fixed pool of energy; you can either grow or reproduce but not both - Wait too long and you may die before reproducing (extrinsic mortality)- When chances of dying are high, natural selection favours individuals who reproduce earlier - Delaying maturity improves survival and the number of offspring - Being a larger mother at the age of first reproduction is advantageous Natural selection balances between two competing factors - Delaying maturity improves offspring survival and number of offspring - Bigger = better as a mother - Wait too long and you may die before reproducing(extrinsic mortality)- Arboreal animals have a longer lifespan than terrestrial onesWhy long for juvenility?Ecological risk hypothesis- Intragroup competition is particularly hard on immatures, so slow and steady growth and development ultimately wins the race- Predictions 1. Juveniles should have lower foraging efficiency than adults a. Ingestions rates of juveniles are consistently lower than those of adults 2. Juveniles should suffer higher mortality from starvation than adults a. Juveniles spend more time acquiring foodb. Juvenile mortality is high during resource scarcity3. Juveniles should suffer more predation a. Juveniles should have lower success at foraging4. Juveniles of species with reliable foods should grow faster than species with unreliable foods Need to learn the hypothesis - Social complexity takes a long time to learn; the juvenile period allows the acquisition of adult competence - Not mutually exclusive with ecological risk hypothesis - Females are copying the moms and following what they are doing - The males are playing (relevant to human behaviour)Play- All primates play - Social play: predominantly “rough and tumble” wrestling, chasing, games of tag- High motivation: seek opportunities; special calls(laughter)faces
The function of social play in primates1. Motor training hypothesis (developing motor function)2. Social relationships hypothesis(developing social relationships)Gorillas- One silverback male and females Motor training:- Male gorillas RS depends upon size and fighting ability - Therefore M need more motor training than F- Predictions - Males play more than juv. females(true)- Males play more with males than females(true)Social relationships:- Gorillas only have strong adult MF bonds - Prediction - Juv. females play more with males than with females (true)How do you measure size in wild primates?- Non-invasive technique: photogrammetry fixed parallel laser as calibration - Distance finder + internal camera properties = absolute size- Males grow slower than females, but they keep growing Class 16: Primate Sexuality Sperm competition- Competition among sperm of two or more males for the fertilization of a single female - Scramble competition only occurs in species with multi-male mating - Results in both morphological and behavioural adaptations - Bigger testes make more sperm - Mouse lemur- largest testicle relative to body size- Longer penis = sperm closer to the egg- in species with multi-partner mating systems - Bone in the penis(baculum)walrus is unusually large - Spines - Might lock the penis into the vagina - Might help in sperm plug removal(solidified sperm- to block the next male) - Might provide biofeedback to males- Proboscis monkeys have black scrota and a red penis that is permanently erect
Mate Choice Darwin's theory of sexual selection - Reduced survivorship by males with elaborate structures is compensated by their advantage in reproductive success- Intrasexual selection: Male-male competition - Intersexual selection: Female Choice/ sexual coercionChoice vs preference - Females may have a preference for high-quality males, but the choice is whether or not they get to act on that preference Male choice- Measures of female attractiveness- Male copulatory size - Male part size - Copulation rate in high vs low-ranking males - Rates of male-male aggression - Strong correlations with the presence of older femalesOrnamentation in humans Class 11- PredationWhy do primates live in groups?Benefits - Safety - Food - Raising offspring Costs- Visibility - Competition - Disease Primates as prey - All primates are vulnerable - Mircrobeus- gorilla - Major predators- Raptors:birds of prey - Felids and other carnivores - Snakes - Primates including humans - Hard to study - Rare events - Studies tend to focus on the prey, not the predators - Predators normally not habituated - Important even if rare- Protective behaviour
Predation can be demographically significant, especially with small primates but even red colobus(10kg adult) suffer high predation - Even people are vulnerable(lions at night)Benefits of group living1. Dilution a. Selfish herd effect2. Vigilance a. The probability of someone being alert to danger increases with group size/can relax vigilance if more neighbours around b. Semantic communication (alarm calls refer to external objects)c. Larger groups= more vigilance 3. Active defence a. If you attack in a group(mobbing), you can sometimes deter a larger predator/can promote cooperation between nonkinb. Individuals take risks to jointly mob a predator c. Red colobus males have been killed while defending against chimpanzees Predation and group composition 1. Number of malesa. Males help in vigilance and defence b. Expectation: high predation risk= higher M:F ratio2. Polyspecific associationsa. Occurs in callitrichidae, cebidae, and cercopithecidaeb. May last for hours or days c. Can be more likely to form when predation risk is high i. Red colobus/diana monkeys ii. Ring- tailed lemurs/Verreaux’s sifaka d. Red colobus behaviour when Diana monkeys present:i. Lower in forest strataii. More feeding on ground iii. Fewer glances down iv. ^ implies less danger when Diana monkeys are present AFTER EXAM 2: Class 19: CooperationCooperation= joint action for mutual benefit - An action that 1) Benefit both the recipient and the actor 2) Provides a benefit to another individual (recipient) but not to the actor(investment, or “altruism”)Hunter-gathers cooperate routinely - Cooperation is operationalized as responding to calls to chase/dig/climb etc- Both sexes cooperate (roughly equally)*Far more cooperation than in non-human primatesWhat explains cooperation in nonhuman primates? KINSHIP
Inclusive fitness theory (kin selection)- Natural selection favors traits that maximize inclusive fitness- Because the actor's genes are spread through both direct and indirect fitnessFitness- Direct fitness- Number of your genome copies you pass directly to the next generation - Indirect fitness- Number of your genome copies passed indirectly to the next generation via kin - Inclusive fitness - Number of your genome copies that are passed in total to the next generation(direct + indirect fitness)Kin selection theory predicts and often finds - More cooperation in philopatric sex - Coalitinoary alliances are prominent among:- Female macaques- Male chimpanzees - But there are instructive exceptions- Ex: Bonobos are male philopatric BUT females more cooperative then males Grooming is altruism - Most instances between mother and infant - Occurs more often between kin than distant kin or nonkinKin Biases in Behavior - coalitions/alliances - Form during disputes- Altruism - Benefit: may result in victory in dominance contest - Cost: risk of injury - Closer kin show more support Kin Recognition A. Phenotype matching 1. Odor 2. Sight B. Familiarity - Via maternal relationship C. The paternal-relationship problem Non-kin cooperation - Contingent reciprocity “helping pays if the beneficiary returns the favor”- Female vervet monkeys (nonkin)- A grooms B- Playback “As distress call”- B’s interest in A’s call increases (compared to control)
Contingent reciprocity maintained by punished - Food calling in rhesus: Low-ranking adult male A discovers food - Implication: reciprocal altruism vulnerable to defection - Males reward A’s altruism (food-calling) by not attacking him Byproduc mutualism - An individuals selfish actions incidentally benefit others The collective action problem - Collective benefit - One (or a few) act, others benefits - This favors “free-riding” - Obtaining benefits without paying - Reduces collective benefit Solving the collective action problem - Kinship has only a small effect of explaining male-male cooperation in chimpanzees(most males are not close kin)- So how do chimpanzees solve the collective action problem?By product mutualism - Other actions increase one's own chances of success - As a consequence of behaving selfishly, the donor inadvertently benefits the recipient - Hunts are more likely to occur if AJ is present - AJ and MS are consistently above the line. This means they tend to hunt first, supporting the evidence of their being “impact hunters”(hunt fist)Group hunting and cooperation - The significance of “impact hunters” - Impact hunters(10% of males) like to initiate hunts- Reasons are unknown - Possibly get more meat - Personalities vary - Impact hunters reduce costs for toher hunters- Hence promote cooperative hunting - This appears to be a general model for cooperation - “Impact individuals” lead the way - Others can then selfishly followManipulative mutualism - Individual B affects the payoff structure such that cooperation is immediately beneficial to Individual ASharing: joint use of monopolizable food items - Passive sharing: co-feeding on the same item/allowing others to take pieces- Active sharing: facilitated transfer/recruitment to a food source Food sharing in wild primates- Kin sharing - Parent/offspring sharing - Orangutans- Chimpanzees
- Capuchins - Spectral tarsier - marmosets/tamarins- Owl monkey- Sibling provisioning - marmosets/tamarins - Yellow-handed titi monkey Food sharing with mates- Associated with monogamous social systems - Mostly male-to-female - Females occasionally share with males - Occurs in birds and humans (Marlowe 2003)- Does not occur in all monogamous species Food sharing with mates - Monogamous primates- Food sharing in captive owl monkeys - Mainly male to female - More donations when F needs more food - Nonkin sharing - Pan paniscus- Carnivory relatively rare - Usually terrestrial verts- Occasionally monkeys - Large fruits- Possession by females - 80% possession by females - No kin advantage - Most sharing passive - Nonkin sharing - Pan troglodytes- Meat sharing (male-male/male-female)Meat for sex- Male chimpanzees exchange meat with females for sexual access - A popular and persistent idea - Supporting evidence:- Gombe: - An early study showed that hunting frequency increased if swollen females present - 5 unambiguous instances of males withholding meat until mating - Mating is frequently observed after successful hunts- Evidence against:- Gombe, Ngogo, Kanyawara - Swollen females NOT more likely to obtain meat
- Sharing did NOT increase chances of mating Social Hypotheses- Meat for sex- Predicts hunting is swollen females present - Negative effect of swollen females - Do males need to entice females? - Promiscuous mating - Females mate with many males - Paternity confusion - Male coercions/mate guarding during fertile period- Females appear to have limited choice - The logic of meat for sex hypotheses is fundamentally flawed Demand sharing - Sharing under pressure - Tolerated theft - Harassment, Manipulative mutualism - Theory - For the possessor, the value of the remaining resource declines with time - Defending food is costly:- Reduced feeding efficiency - Risk of injury - Allowing beggars to take some food saves costs of defense Chimpanzees(Gombe) possessors of meat harassed (sometimes gently, sometimes forcibly) by others trying to tear off chunks for themselvesThe possessor who completely defends his food has to cover it with his arms- so he cannot eat it!Demand sharing predictions- Harassment by beggars is costly to the professor - Harassment elicits sharing - Harassment declines after sharing Harassment imposes real costs: possessor eats slower when harassed by more beggars More harassment = more sharing Sharing reduces harassment Demand sharing … possessors pay beggars to go away Tolerated theft or demand-sharing - Recipients take from possessors /have some control over donors - Donors allow to be taken (do not give) offer minimal resistance - Theory: Recipients: persistence or fighting gives high benefits (even small amounts of meat give high-valueDonors: fighting gives low benefits (possess too much meat to eat; no storage)Favored by: lack of donor control
Class 21: Culture“Now we must define tool, redefine man, or accept chimpanzees as human”- Louis LeakyCultural evolution, not only genetic evolution, proceeds by a Darwinian process- Variation - Inheritance (not only from parent but from others in the social group)- Competition - Differential success- Relies on social learning Studying cultural behaviors in nonhuman primates helps us understand how human cultural capacities evolved - CCE: cumulative cultural evolution- adaptive modifications accumulate over evolutionary time, leading to incremental improvement of material and symbolic artifacts, as well as complexity Culture: that complex whole which includes knowledge, belief, art, morals, custom and any other capabilities and habits acquired by man as a member of society. - Tylor 1871- Broader view: a cultural behavior is one that is transmitted repeatedly through social or observational learning to become a population-level characteristicHow animal ethologists recognize culture- Behavioral variation among populations that “cannot be explained by genetics or ecology”- Ex: termite fishing is found wherever “fishable” macrotermes occur (probably ecological)Is variation cultural or ecological - No ecological explanation- must be culturalWhen genetic and environmental factors are controlled, wild chimpanzees rely on their cultural knowledge to solve a novel taskTools- Capuchins: the first monkey known to obtain food with tools - Rare case of capuchins occupying the savanna - No terrestrial predators - Select the heaviest or least fragile rocks - Get important amounts of food*Stone tools improve diet quality in wild monkeys - In bearded capuchins - Tool use does not change diet quantity - But it does improve diet quality - Lower fiber, more energy - Protein intake similar across days
Teaching- Teaching is characterized by the active involvement of experienced individuals in facilitating learning by naive conspecifics Meerkats- Criteria for teaching: all true for meerkats(decide that A teaches B)1. A modifies its behavior only in the presence of B 2. A incurs some cost or at least does not obtain an immediate benefit 3. B acquires knowledge or learns a skill in life or more rapidly or efficiently than it would otherwise do, or it would not learn at all- To date, the most convincing evidence of teaching in non-humans comes from meerkats, not primates Observational learning - Daughter chimpanzees practice and learn termite fishing faster and more thoroughly than sons a) Daughters spent more of their time at termite mounds engaged in fishingb) Daughters copied their mother's choice of tools. Sons did not c) Daughters obtained more termites per dip Social facilitation = activity of others that indirectly increases the chances individuals will learn behaviors- great tits: attention drawn to an oppurtunity to get food- and each figures the solution out Observational learning learning to perform actions or behaviors by watching others. Includes imitation - Experiment is needed to distinguish observational learning from social facilitation Summary- No evidence of teaching in primates- Transmission of knowledge/skills is not necessarily through observational learning - Whiten et al. Pan-pipe study: chimpanzees can obtain skills via observational learningClass 22: Primate ConservationOne of the richest mammalian ordersPrimates: 504 species form 79 genera and 16 families- ⅔ of all species occur in just 4 countries - Brazil, Madagascar, Indonesia, Democratic Republic of Congo What predisposes species to extinction risk?- Small population size - Small geographic range - Island endemism - Higher trophic levels - Slow lifes history - Complex social structures - Large ranges - Diurnlity - Large body sizeThe anthropomorphous apes… will no doubt be exterminated(Darwin)
Ecological importance of primates - Primates are prey, predator, and mutualist species in food webs and can thus influence ecosystem structures, functions, and resilience- Seed dispersal - Endozoochory = swallowing and defecationIn the past few thousand years, at least 17 species of lemurs have gone extinct Extinct lemurs are larger seeds Some large seeded Malagasy plants don’t have modern dispersers What are the threats to primates?- Human population growth - Urban population growth - Agriculture - Logging- Hunting/trapping - Farming - Pollution- Climate change - Civil unrest - Roads and rail Class 23: Primate EnergeticsOrigin or Homo Sapiens= 300kyaOrigin of agricultue = 10kya- For 95% of the history of Homo sapiens, we have lived as hunter-gathers - Hunting and gathering are likely responsible for the evolution of many uniquely human traits- Hunter-gathers were portrayed as animalistic, on the edge of starvation- This changed with the Orginal Affluent Society (Marshall Sablins)- The origin of the 15 hour work week - “How will all keep busy when we only have to work 15 hours per week”- John Maynard Keynes How do primates acquire and burn energy?How do humans do it differently?- Primates have slow life histories comapred to other mammals - How?- Metabolic deceleration - TEE= total energy expenditure(number of calories burned during this day)- Measured using isotopically tagged water that is consumed, and then urine is collected. Decay of the isotope in the urine gives TEE- For a given body mass, primates have lower TEE than non-primate mammalsPrimates decelerated their metabolisms Humans accelerated their metabolisms relative to other primates- Must take into account phylogenetic context Humans take a long time to develop, but they produce large surpluses as adultsHumans work fewer hours per day than other great apes
Humans get a lot of food compared to other great apesHunter-gathers produce a lot AND rest a lot Bipedalism makes humans more efficient at walking, helping them cover more territory to acquire high-quality resourcesLocomotor economy in humans and chimpanzees- Humans have U-shaped walking efficiency (cost of transport)- Chimpanzees don’t (grey line)- Humans walk more efficiently than chimpanzeesHumans have fewer muscle activations when walking compared to chimpanzees- lower energetic costs - Human walking is extremely efficient. This is why going for a walk won't easily burn the calories from a donutChimps are 1.5x stronger than humans How do humans and chimpanzees compare in terms of:Locomotor economy?- Humans better- enables longer day range to acquire higher quality resources Strength?- Chimps built for strength, humans for enduranceClass 24: OverviewArdipithecues Ramidus(Ethiopia 4.4mya)- Capable of bipedalism in trees and on the ground - Chimpanzee sized brainAustralopithecus afarenis (Ethiopia 3.5 mya)- Human-like from the waist down - Chimp-like from the waist up - High sexual dimorphism in body size Emergence of modern humans (300 kya)What makes us human?- “The evolution of fundamental prosocial attitudes”- Prosocial means “cooperative and or altruistic”- Shared intentionality is also key - Ability and motivation to engage with others in collaborative, co-operative activities with joint goals and intentions- The fundamental source for the majority, if not all, of our unique cognitive achievements- Cooperation, language, complex technologies, art, formalized norms and institutions, religion The aggression problem - rousseau/hobbes debate - Compared to primates… which view of humans is more accurate.- Man is born free and everywhere he is in chains ® humans are naturally cooperative, unaggressive - Solitary, poor, nasty, brutish, and short (H) humans naturally competitive and violent
To resolve debate: recognize 2 types of aggression Reactive vs Proactive - Throughout human evolution, reactive aggression has been reduced BUT proactive aggression is very important(war, torture, homicide, capital punishment)In the 17 years that Hill and Hurtado worked with Ache foragers, they never observed a scuffle between Ache men- Human males scuffle at 1/1000th chimpanzee rate - Reactive aggression very reduced in humans Chimps more aggressive than bonobosDomestication syndrome 1. Selected traited a. Reduction in aggression 2. Unselected traits a. Reduction in brain size b. Reduced muzzles, teeth c. White patchesSelf-domestication should operate similarly Hugely less aggressive behavior in bonobos - Within group or between group killing whether they are captive/wild or male/female - Less aggressive anatomy in bonobos - Shorter canines - Cranio-facial feminization- Reduced sexual dimorphismSelf-domestication syndrome in bonobos 1. Selected traits a. Reduction in aggression 2. Unselected traits a. Reduction in brain size b. Reduced muzzles, teeth c. Paedomorphic behaviori. Later offspring independenceii. Retain tolerance longer iii. More adult play iv. More adult homosexulaity d. Paedomporhpic behavior i. Whitetail tuft maintained latere. Paedomorphic cognition i. Later development of inhibition f. Pink lipsHunting and gathering (2mya)- Central place foraging - Not seen in any other primate; bring back food to share at central place- Widespread food sharing of hard to acquire food- Intergeneration food transfer
- Egalitarianism - Cooling the heart of the hunter to reduce the chance of individual domination Modern homo sapiens - Brain reduction in the last 30,000 years - Short face, small teeth - Reduced sexual dimorphism in skulls and post-cranial skeleton - Paedomorphic behavior Counter-dominance and capital punishment Counter dominance/reverse dominance hierarchy = teaming up on an upstart or bully - Requires language to coordinate attack - Can result in sanctions or capital punishment Victims of capital punishment in small scale society: BOTH MALE1. Aggressors 2. Noncooperators Occurs everywhere as a method of social control NOT possible in baboons/chimps because they cannot coordinate counter-dominanceIn a world without prison or police, capital punishment is the only way to stop an unrelenting bully- Key point that reconciles Hobbes and rousseau (selection against reactive aggression via proactive aggression)