human evolution exam 2

Three main primate tendencies 

1. Adapted for a lief in the trees (arboreal adaption)  

2. Eat a variety of foods (dietary plasticity) 

3. Invest a lot of time and care in few offspring (high degree of parental investment)  

 

Dietary plasticity  

• Lack of dietary specialization – generalized feeders (omnivorous) with generalized dentition  

• 4 types of teeth:

  • Incisors and canines: biting and cutting  

  • Premolars and molars: crushing and grinding  

Parental investment 

1. Relatively long gestation periods  

2. Few offspring, delayed maturation, longer lifespan than other mammals 

3. Greater dependence on learned behavior  

4. Relatively large and complex brain  

Arboreal adaption hypothesis  

• Traditionally, the arboreal adaptation seen as the primary factor in primate evolution  

  • Selected for 3D and color vision  

  • Grasping prehensile hands/feet 

  • Tropical arboreal environment = varied foods  

Visual predation hypothesis  

• Primates evolved in bushy forest undergrowth relying on insect diet  

• Grasping hands and vision for grabbing insects 

• Tree jumping/ climbing is a result 

Two suborders 

• Prosimii (strepsirrhini)  

  • Lemurs, lorises, tarsiers  

• Anthropoidea (haplorhini)  

  • Monkeys, apes, humans  

Promsimians

• lemurs and lorises

• Most primitive  

• Greater reliance on olfaction (long snouts) 

• Mark territory with scent 

• Shorter gestation and maturation 

• Unfused mandible and frontal bones  

• “Dental comb”, grooming claw

Tarsiers 

• Nocturnal  

• SE Asia  

• Mated pair and offspring  

• Diet: insects and small vertebrates 

• Difficult to classify 

Anthropoids

• monkeys and apes

• Larger body, larger brain  

• Eyes fully forward; postorbital closure 

• Fused mandibles, frontal bones 

• Longer gestation; longer maturation; increased parental care  

Catarrhines vs. Platyrrhines 

• Catarrhines  

  • Owm (old world monkeys) and apes  

  • Nostrils closer and downward 

• Platyrrhines 

  • Nwm (new world monkeys) 

  • Well separated nostrils  

New world monkeys 

• Almost exclusively arboreal  

• Prehensile tails (some) 

• Two (size) groups:  

  • Callitrichids  

  • Cebids  

Callitrichids (marmosets and tamarins)  

• Claws instead of nails 

• Twins rather than single births  

• Family groups  

  • Mated pair  

  • 2 males and 1 female  

Cebids 

• Larger than callitrichids  

• 30+ species  

• Diet varies with combo of fruits and leaves  

• Most are quadrupeds  

• Spider monkeys are semibrachiators  

old world monkeys

• Two subfamilies 

  • Cercopithecinae 

  • colobinae 

cercopithecinae  

• Many exhibit  

  • Sexual dimorphism  

  • Ischial callosities  

• More generalized than colobines  

• More omnivorous  

  • Cheek pouches to store food while foraging  

Colobines  

• Leaf diet, sacculated stomach  

• Colobus monkey exclusive to Africa  

• Langurs found in Asia  

• Proboscis in Borneo  

OWM vs. Ape molars 

• OWM  

  • Bilophodont molars 

• Ape 

  • Y-5 molars  

Hominpods

• humans and apes

• Gibbons and siamangs  

• orangutangs

• gorillas

• chimpanzees

ecology

the interrelationship between an animal and its habitat  

adaption

the process by which a species changes or adjusts to its environment – can be anatomical or behavioral  

Ecology affects 

• Behavior  

  • Type of foraging strategy  

  • Type of social group  

  • Size, # of males and females  

• Anatomical structure  

  • Type of locomotion  

  • Type of dentition  

The ecological niche  

• Where you live (habitat)  

• What you eat (diet) and how you extract it (foraging strategy) 

• When you are active  

• How you move  

primate habitats

• Two types of tropical/subtropical habitats  

  • Tropical rain forests  

    • Moist, less seasonal, more trees 

  • Tropical woodland savanna  

    • Drier, more seasonal, less trees  

tropical rain forests

• Climate  

  • Equatorial belt  

  • Warm temperature  

  • High annual rainfall  

  • >60 inches  

  • Consistent: less seasonality  

• Primates 

  • Arboreal  

  • Specialists  

  • High species richness  

tropical woodland savanna

• Climate  

  • N or s of equatorial belt  

  • Temperature is not constant  

  • Lower humidity  

  • Less rainfall  

  • Dry seasons  

  • More seasonal  

• Primates 

  • Less species richness 

    • No more than 4 or 5 species  

    • Generalists  

    • Terrestrial primates  

      • Many old world monkeys such as baboons or macaques  

What's so important about diet  

• Influences all aspects of a primates life 

  • How nutritious is the food you eat?  

  • Do you have to compete for food? 

  • Is the food available year round? 

  • Are you limited by your food? 

What limits diet choice

• Nutritional requirements 

• Habitat  

• Quality of food and tradeoffs  

• Body size  

• Food distribution  

requirements of diet

• Satisfy energy requirements 

• Calories 

• Provide specific nutrients  

• Proteins, fats  

• Vitamins, minerals  

• Water 

• Minimize exposure to toxins  

how much diet do you need

• Basal metabolic rate (BMR) 

• Active metabolism  

• Growth  

• Reproduction  

diet types

• Frugivory  

• Folivory  

• Insectivory  

• Gumnivory  

• Graminivory  

• Semnivory  

diet tradeoffs

• Insect, small animals 

  • High quality, but small and hard to find  

• Fruit  

  • High energy, but low protein 

• Leaves 

  • Abundant. Protein, but low quality, and toxins  

• Seeds and grasses  

  • High quality but small, hard to get at and toxic  

size and food

• Big body, lower metabolism: can survive on low-quality food, but need lots of it! 

• Small body, higher metabolism: need high-quality, quickly digested food, but only need a little (ex. Tarsier, mouse)  

food distribution

1. Space 

• Clumped 

  • Found in patches; everybody competes  

• Evenly distributed  

  • All over, everyone spreads out  

2. Time-seasonality 

• Seasonal habitats  

  • Diets must change during the year 

  • Food shortages  

• Non seasonal  

  • Constant food supply 

activity patterns

• Diurnal  

• Nocturnal  

• Cathemeral  

• Crepuscular  

primate locomotion

• Vertical clinging and leaping  

• Quadrupedalism  

• Suspension  

• Knuckle-walking  

• Bipedalism  

Quadrupeadalism  

• Aroboreal  

  • Adapted for branches  

  • Shorter limbs  

  • Curved digits  

  • All new world monkeys, colobines 

• Terrestrial  

  • Adapted for the ground 

  • Longer limbs  

  • Short digits  

  • More stability in shoulder and elbow  

  • Some OW monkeys  

Suspensory locomotion  

• Arms longer than legs 

• Very long forelimbs 

• Mobile joints 

• Curved digits (fingers and toes) 

• Only “true” brachiators are gibbons  

Primatology 

• Study of primate behavior and ecology  

  • Behavior is an adaption to environment 

  • Behavior is result of evolution: natural selection  

primates problem

• Get enough food  

• Avoid becoming food  

primates solution

• Live in social groups  

  • Benefit avoid predation  

    • More individuals = more eyes  

    • Dilution effect 

• Cost: more individuals = more noticeable to predators  

• Benefit: others help find food protect food supply from other social groups 

• Cost: food competition 

  • Group can't be too big  

• Relationship between group sixe and other group encounter success for capuchin monkeys  

resource defense model

• Animals group together to defend resources  

• Upper limit to group size  

  • Too big: disadvantage, too much within group  

• Ways to resolve within group conflict  

  • Dominance hierarchies  

Dominance hierchies resolve within group conflict  

• Individuals ranked relative to each other  

• Access to resources  

• Reduce aggression  

• Rank not permanent  

• Rank may be inherited  

• Can affect reproductive success  

Predator avoidance model  

• Live in groups for defense against predators  

• Benefits of reduced predation risk outweighs costs of within-group competition  

• The two models interact: 

• Predator avoidance: minimum size  

• Resource competition: maximum size  

social benefits of living in a group

• Learning is easier 

• Finding a mate is easier  

• Sharing information is easier  

• Assistance in rearing offspring  

• Divisions of labor are possible  

social system

The grouping pattern in which a primate species lives, including its size and composition, evolved in response to natural and sexual selection pressures  

elements of a social system

• Group size and composition  

• Use of the environment 

• Breeding/mating system  

• Nature of intragroup social behavior  

• Emigration pattern  

ranging patterns

• Home range: the spatial area used by a primate group  

  • The area that contains all the resources used by group members for feeding, resting, and sleeping  

• Territory: an exclusive home range defended against other groups  

territory defense

• Benefits: prevents outsiders from exploiting resources  

• Costs: vigilance, energy of defense  

philopatry

staying in ones natal (birth) group as an adult  

• females

dispersal

leaving group upon reaching puberty 

• males

principles of sociobiology

• Behavior has some genetic basis  

• Behavior is subject to process of evolution by natural selection in the same way as morphology  

Reciprocal altruism

help now in exchange for help later 

• certain conditions must be met

  • Frequent interactions  

  • Individual recognition 

  • Way of punishing cheaters 

  • Long term benefits outweigh costs  

the logic of natural selection

• More individual are born each generation than can survive and reproduce which results in competition among individuals 

• There is biological variation both morphological and behavioral among individuals 

• Individuals who possess certain favorable traits whether morphological or behavioral have a better chance of surviving or reproducing than other individuals who lack those traits and will thus 

Degree of relatedness of “r” 

• Full siblings ½ 

• Half siblings ¼  

• Parent-offspring ½ 

• Grandparent-grandchild ¼  

• Aunt/uncle - niece/nephew ¼  

• Cousin 1/8 

inclusive fitness

• An indivudals total genetic contribution to the next generation  

• Includes own direct fitness plus indirect fitness devalued by “r”  

• DF + r x IF 

hamiltons rule

• B x r > C 

• B = benefit to recipient  

• C = cost to actor  

• r = degree of relatedness between actor and recipient  

kin selection

Process by which traits or behaviors arise via natural selection through their effects on the survivorship or reproduction of relatives  

male and female stradegies

• Male reproductive success: limited by access to mates 

• Female reproductive success: limited by access to resources (pregnancy and lactation are energetically very expensive)  

Determinants of social groups  

• Females distribute themselves based on distribution of resourecs 

  • Fruit  

  • Leaves 

  • Insects 

• Males: distribute themselves based on where females are  

• Males – females – food  

types of social systems

• Solitary (noyau)  

• Monogamy 

• Polygyny: 

  • One male, multi female 

• Polyandry  

  • One female, multi male  

• Polygynandry  

  • Multi male, multi female (fission-fusion) 

Solitary/noyau 

• Usually nocturnal, solitary animals 

• Meet only to mate 

• Male ranges overlap females  

• Both sexes disperse 

• Orangutans  

• Strepsirhines  

polygyny

• Single male- multi female group and bachelor males  

• Groups that consist of one or more males and multiple females  

• Polygyny = multiple females  

• Characterized by complex social interactions 

• Dominance hierarchies  

• Mate guarding 

• Male male competition  

• harem 

• Usually female philopatry  

• Bachelor males  

• Multiple male influxes 

• Gorillas  

dominance hierarchy

ranking determined by contests (fights) 

• Multi male groups: males compete for dominance 

• Females have dominance hierchies too! Food  

infanticide

• The killing of infants, either by members of the infants group or members of a rival group 

• Usuallt happens during male takeovers 

• Male strategy  

  • Get females ready to conceive (in estrus) 

polygynandrous

• Multimale – multifemale social group (with male emigration) 

• Vervet monkey 

• Mate guarding impossible  

• Sperm competition  

• Paternity confusion  

fission fusion

• Multi male, multi female 

• Animals travel in foraging parties of varying sizes instead of in cohesive group 

• Response to patchy food distribution and competition for food  

sexual dimorphism

difference in body size or form between sexes  

• Larger or smaller body size  

• Secondary sexual characteristics: pelage, coloration, canines 

• One male multifemale: males much larger 

• Multi male, multifemale: males usually larger 

competitive males

• High ranking males attempt to monopolize conceiving females  

• Male rank is correlated with reproductive success  

• Male reproductive success tied to number of different females he can mate with  

Infanticide

sexually selected male reproductive strategy 

• If unweaned infant dies, female resumes cycling immeadiatelt 

• Death of infant makes females available for mating sooner 

• Infanticidal males gain immediate mating opportunities  

• If male tenure is short, infanticide enhances male  

Counterstratgies to thwart infanticide  

• Defend victims of attack  

  • Mothers

  • Female kin  

  • Males present at conception  

• Confuse paternity  

  • Estrus swellings  

  • Mate with many males  

  • Mate with newcomers 

primate communication

• Tactile (touch) 

• Olfactory (smell)  

• Optical (see) 

• Auditory (hear)  

tactile

• Hugging, kissing, and grooming are forms of reconciliation  

• Provides feeling of well-being, reassurance  

• Often lifelong relationships  

olfactory

smell

• Prosimians (strepsirrhines): rely heavily on smell 

• Anthropoids (haplorhines): smell is reduced  

chemical signals/ pheromones

• Territory defense 

  • Body secretions  

  • galagos and pottos urine mark four times more frequently near the periphery of their ranges than in the center 

• Scent marking  

  • Marking territory  

  • Ring-tailed lemurs scent marking/ olfactory signals  

sexual receptivity

nonhuman primate females indicate readiness to mate through olfactory cues 

• Males often smell the perineal region of the female 

“sweaty T-shirt" study  

• Clause wedekind 1995  

• Had males where the same shirt and not shower  

• They put the tshirts in bins and the male and females were split by their immune system 

• Had the females rate the scents  

• Females perfered the immune system that differed from theirs  

optical

• One animal gains info from another by looking at it  

• Not only facial signals but how an individual spaces itself, and its body postures  

• Anthropoids (haplorhines) have better innervation to their muscles of facial expression than do prosimians  

auditory

• Species recognition  

• Each species has a unique repertoire  

• New species of busy babies and tarsiers discorved on the basis of their vocalizations  

• Within and between group distinctions  

• Territory defense – long distnace vocalizations communicate whereabouts and allows members of different groups to avoid or approach each other  

Traditional view of non-human primate communication  

• Involuntary  

• No syntax  

• Affective vs. referential  

• Not symbolic  

Origins of human language  

• Primates do not learn or use language the same way as humans  

• Vocal tract and brain (broca’s area) adaptions for language  

  • Broca's area larger on left side in humans, chimps, and gorillas  

• Captive studies  

• Chimps and gorillas can interpret visual signs (sign language) and use them to communicate  

• Can teach each other  

• Can categorize new objects

human culture and communication

• Larger brains, complex learning  

• Think symbolically and use language  

• Adaptive strategy = culture  

Why are primates brains so big?

• Could have to do with  

•  finding food 

• Social engagement 

What selection pressure favors intelligence in primates? 

1. Ecological factors associated with locating and processing inaccessible food items 

2. Social factors associated with life in large complex social groups  

Ecological intelligence – selection would favor:  

• Spacial mental maps of food trees 

• “temporal maps” for sseasonal food 

• Ability to find and extract “hidden” foods (hard shelled nuts, buried roots and tubers, insect larvae in tree bark)  

• Ability to use tools to access food  

 

Social intelligence – selection would favor:  

• Ability to:  

• Deal with conflict and competition  

• Reconcile disputes (make peace)  

• Form dominance hierarchies  

• Form coalitions and enduring social bonds  

• Engage in reciprocity  

• Deceive others, detect deception  

“social brain hypothesis” (Dunbar 1998)  

• The view that our cognitive capacities constrain the size of primate societies (number of friends) 

• Alternatively, social complexities drove brain size to an upper limit related to group size  

primate brains

• Primate brains are adapted for an arboreal lifestyle  

• Significant adaption in the areas that process visual information 

• Primates are very good at depth perception and shape recognition 

Anthropoids (haplorhines) 

• Developed a diet focusing largely on fruit, unlike the very insectivorous prosimians (strepsirhines) 

  • Mental maps, group formation, territories 

• Even larger brains, especially the portion related to shape recognition  

Anthropoid visual system  

• Developed a much-heightened ability to recognize faces and facial expressions  

• Connections between amygdala (emotional brain) and neocortex (cognition, reasoning)  

• Can use facial expressions to communicate – and can interpret – emotional states  

• Social behavior further drives the evolution of brain size  

Frugivore vs. Folivore brains  

• Folivores have smaller brains than frugivores  

  • Gut needs to be very long to digest leaves  

• Heavy metabolic investment in digestion  

  • The balance cannot be made up by decreasing heart, kidney, or liver 

• So... brain size must be limited in folivores  

• Is there a selective release on frugivore brain size? Or reduction in folivore brains?  

deception

• behavior that acts to persuade another to believe something is false  

• Examples in primates:  false alarm calls, hiding to mate  

theory of mind

• Deceptive behavior in primates suggests the ability to think about what another individual is thinking  

• Knowing that other individuals have minds and beliefs, and these beliefs may differ from one's own beliefs  

• “Mind reading”  

• Usually evaluated through “false belief test”    

The machicavellian hypothesis  

• The most complex part of a primate's daily life is the everchanging nature of (multiple) social interactions 

• Success in reproduction and access to high-quality foods requires constant monitoring of one's social standing  

Tactical deception  

When one individual misleads a second individual in order to obtain some immediate goal, normally available to or under control of the second  

mirror recognition test

• Monkey and gorillas invariably FAIL  

• Chimpanzees sometimes pass/sometimes fail  

• Chimpanzees that are raised in human conditions are the most likely to PASS 

What do anthropoids do that might have set the stage for theory of mind  

• Theory of mind is evident in humans, but no clear evolutionary antecedents  

• There is a correlation between theory of mind and general problem-solving ability 

• It is very harcd for anthropoids to inhibit emotionally based facial responses because they are largely involuntary  

• This may explain their poor performance on many false belief tests  

• Anthropodis do use tactical deception, but without theory of mind they are relatively poor liars  

Criteria for cultural acts in other species  

• Innovation: new pattern is invented or modified  

• Dissemination: pattern is acquired (through imitation) by another from an innovator  

• Standardization: form of pattern is consistent and stylized  

• Durability: pattern is performed without presence of demonstrator  

• Diffusion: patterns spreads from one group to another  

• Tradition: pattern persists from innovators generation to the next 

• Nonsubsistence: pattern transcends subsistence 

• Naturalness: pattern is shown in absence of direct human influence  

Leaf clipping: symbolic behavior 

• In some communities 

  • Done by males – aggression, frustration  

• In other communities  

  • Done by males and females to indicate grooming or copulation interest, “flirting”