Chapter 5

Why we study primates:

1. Reasoning by homology 

• We share inherited similarities in anatomy and behavior 

2. Reasoning by analogy 

• How does evolution shape bodies and behaviors? 

3. Interpret human fossils

•  adaptations in environments occupied by ancestors 

What is a primate?

1. Physical

• Grasping hands and feet (opposable thumb)

• Nails instead of claws 

• Enhanced vision, reduced olfaction 

• Forward facing eyes encased in bone 

2. Movement

• Hind limb driven locomotion 

3. Life-history

• Long gestation

• Small liters (one or two)

• Long juvenile period 

• Long lifespan 

4. Teeth 

• All primates have 

1. Incisors, canines, premolar, molars 

2. Formula is I-C-P-M

• Humans and Catarrhines are 2:1:2:3

• Unspecialized molar teeth 

5. Location 

• Tropical animals, mostly forest dwelling

• Modern range: central and south america, africa, asia 

• Fossil range: included north america and europe 

Strepsirrhines:

• Features 

1. Mostly nocturnal 

2. Mostly solitary 

3. Tooth comb

4. Claws 

5. Acute sense of smell

6. Wet noses (rhinarium)

7. Slightly smaller brain 

8. Tapetum (reflective layer in back of eye)

9. Scent glands

• Two Infraorders

1. Lemuriformes (lemurs)

2. Lorisiformes (lorisi, galagos, pottos)

Haplorrhines 

• Tarsiformes (tarsiers), platyrrhini (New world monkeys), and Catarrhini (Old world monkeys)

Platyrrhines (New World Monkeys)

• Live in mexico, south and central america

• Mainly diurnal

• Tropical forests

• Arboreal - many have prehensile aka grasping tails 

• Quadrupedal through some suspensory climbers 

• 2-1-3-3 dental formula 

Suspensory locomotion traits

• Longer arms than legs

• Long fingers

• Shortened lumbar region of the spine 

Catarrhines (Old World Monkeys and Apes)

• Live in africa and asia 

• All diurnal

• Some arboreal some terrestrial

• Broad habitat range

• Larger body size 

• Large groups 

1. Male dispersal; female bonds 

• Dental formula 2-1-2-3

• Old World Monkeys have tails and parallel ridges on molar teeth

• Apes have no tail and no ridges 

Hominoids (Apes)

• Lesser apes (Hylobatidae) 

1. Asian apes

2. Gibbons and siamangs 

3. Arboreal, brachiators 

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• Very long arms, swing across gaps in forest canopy 

4. Pair bonding; male parental care

5. Males and females sing coordinated territorial duets to establish and maintain territory 

• Great Apes (Hominidae)

1. Orangutans (Pongo)

• Found only in tropical rainforests of Borneo and Sumatra

• Largest arboreal animal in the world 

1. Arboreal means long arms and long curved fingers and toes

• Eats fruits, leaves, and bark 

• Most solitary anthropoid

• Intense male/male competition for mates

1. Males defend home ranges of adult females and attack other male trespassers

2. Gorillas (Gorilla)

• Three subspecies 

• Exhibit marked sexual dimorphism 

• Spend little time in the trees 

• Spend most of the day feeding on ground plants, leaves, bark, fruits, and other vegetation

• Live in troops of  males and females with offspring

3. Chimpanzees (Pan)

• Light faced infants

• live in large groups, males and females together

• “Fission-fusion”

• Often split into smaller parties, which are not always composed of the same members

• These smaller, temporary groups change depending on the activity

• Well studied

• Live in equatorial africa

• Knuckle walk and tree climb

• Female dispersal

• Diverse diet: fruit, vegetation, insects, meat 

• Sophisticated tool use

1. Termite fishing poles

2. Using leaves as sponges 

3. Rocks to crack open nuts

• Highly intelligent 

4. Bonobos (Pan)

• Dark faced infants 

• Pink lips 

• live in large groups, males and females together

• “Fission-fusion”

• Often split into smaller parties, which are not always composed of the same members

• These smaller, temporary groups change depending on the activity

• Hippies very much peaceful 

• Live in small area in democratic republic of congo

• Not well studied

• Female dispersal 

• Eat fruit, vegetation, some meat 

5. Humans (Homo) 

• Global species 

• Diversity in social and mating organization with tendency to pair bond 

• Diversity in diet, primarily omnivores 

• Complex verbal language 

Bonobo Socio - sexuality 

• Sexual activity separate from reproduction

• Diverse sexual behaviors

• Face-to-face sexual interactions with genital contact between females  (unique among primates)

• Reducing tension, promoting bonding

• Occurs after aggressive conflicts (repair social relationships) or when groups come together (build new relationships)

Why the difference in behavior between chimps and bonobos?

• Richer food patches and less periods of food scarcity in forests inhabited by bonobos = relaxed competition 

• Female bonobo sexuality, more female centric society, lower aggression 

Apes 

• Larger body and brain size

• Longer life span

• Longer intervals between births 

• Tendency toward upright posture

• Shorter and lesser projecting face and muzzle

• No tail

• Locomotion:

1. Suspensory and vertical climbers

2. Gorillas, chimps, and orangutans spend considerable time on the ground. 

Primate Ecology 

Primate Diets 

• Protein 

1. Insects

2. Animal prey

3. Young leaves

• Carbohydrates

1. Fruit 

2. Gum 

• Fats and Oils 

1. Insects and animal prey 

2. seeds

Diet Specialization 

1. Insectivores

• Small body size 

• Sharp cusps on teeth

• High, sharp crests of molar teeth

• Simple digestive system 

2. Folivores

• Large body size

• Small, sharp incisors

• Sharp shearing crest on molars

• Enlarged, well developed digestive system

3. Frugivores

• Medium body size 

• Large broad incisors to puncture rind of fruit 

• Low cusped relatively flat molars (crush) 

• Relatively large digestive system, but not as large and complex as folivores 

4. Gummivores 

• Small body size 

• Claws in some

• Long robust incisors 

• Some have projecting incisors and canines to scrape bark from tree 

• Unspecialized digestive system 

Among primates, folivores tend to have 

• Small sharp incisors 

Home Range Versus Territory 

• Home range: the entire area occupied by a primate group

• Within the home range is a core area where the group is more frequently

• This core area (“Territory”) is defended against intruders

• Other parts of the home range might overlap with other groups, but not the core area

Gorillas:

• Leaves and other vegetation

• Small home range b/c

1. Vegetation = Hyper-abundant

Chimpanzees:

• Fruit, some leaves, some red colobus monkeys

• Large home range b/c

1. Travel far to find ripe fruit

2. Different fruit ripen at different times

How does the diet of a primate affect its home range?

1. Availability of food

• Leaves and seeds are often more plentiful than fruit.

2. Seasonality of food

• Ripe fruit and leaves are not always present.

Primate Territoriality 

• Varies by species

• Costs:

1. must defend the area 

2. Dangerous aggressive interactions 

• Benefits:

1. Can protect limited resources such as mates and food

• If benefits outweigh cost then territoriality is favored however is resources not limited the cost is likely larger than the benefit 

Dominance 

• Many primates organized in dominance hierarchies

• They reduce violence as dominant individuals can threaten without attack 

• Males and Females

1. Separate hierarchies 

2. Males dominant over females besides lemurs and bonobos 

3. Monogamous pairs are codominant 

• Female Hierarchies:

1. Mother rank

2. Can change during life depending on age, aggression, time in the group, intelligence 

• Dominance learned as infants

1. Infant observes how mother responds to others and how she treats others 

2. Gestures, fascial expressions behavior 

3. As they get other they play wrestle with peers 

Communication 

• Many intentional forms such as gestures, facial expressions, vocalizations 

• Displays (complex combinations of behaviors example: tortillas chest slapping 

• Threatening communications 

1. Intense stare

2. Branch breaking 

3. Yawn to show canine teeth 

4. Crouch bobbing back and forth 

5. Mounting 

• Submission 

1. Crouched position 

2. Presented hindquarters 

• Reassurance 

1. Touching, patting

2. Grooming

3. Hugging, holding hands 

Grooming:

• Using fingers to pick through fur of another individual

• Hygiene: removes dirt and insects 

• Pleasurable, comforting 

• Mothers groom infants

• Males groom sexually receptive females 

• Subordinates groom dominants 

• Restores peaceful relationships after conflict 

Defense against Predators:

• Fleeing or taking cover

• Vocalizations

• Interspecific associations 

• Increased group size 

1. Detection: more eyes to see predator 

2. Deterrence: mobbing behavior 

3. Dilution: lowers individual risk of death 

Why are Primates Social?

• Benefits 

1. Avoidance of predators 

2. Feeding competition (defense of food patch)

• Costs

1. More competition for food and mates 

2. Increased disease transmission  
   

Primate Social Systems

1. Polygynandry 

• Multiple males, multiple females 

• Both males and females mate with more than one partner 

• One of the two most common forms of social organization in primates

2. Polygyny

• One male, multiple females 

• Male mates with multiple females, but females mate with the resident dominant male only 

• Intense male - male competition 

• One of the two most common forms of social organization in primates

3. Bachelor Groups

• Travel together

• Hierarchical

• Waiting for future opportunities (most=none)

• One may challenge the resident male (not coalition)

4. Monogamy

• Pairs

• Some extra-pair copulation 

5. Solitary 

• Associated with polygyny 

• Adult female home range is alone or with dependent offspring 

• 1 males territory overlaps with several adult females

Viviparity: The trait of giving birth to live young.

Conspecific: A member of the same species.

Sexual Dimorphism: Differences in body size or morphology between sexually mature males and females.

Opposable thumbs: Of a thumb or big toe: capable of touching one or more of the remaining digits of the same hand or foot. Most primates, including humans, have an opposable thumb, whereas most primates, but not humans, also have an opposable big toe and can bend their big toe to touch the other toes on the same foot.

Hind limb dominated: A form of locomotion that depends mainly on the hind legs for power and propulsion.

Molar: A broad, square back tooth that is generally adapted for crushing and grinding in primates. Anthropoid primates have three molars on each side of the upper and lower jaws.

Incisor: A front tooth in mammals. In anthropoid primates, incisors are used for cutting, and there are two incisors on each side of the upper and lower jaws.

Canine: A sharp, pointed tooth that lies between the incisors and the premolars in primates.

Premolar: A tooth that lies between the canines and molars.

Brachiation: A form of arboreal locomotion in which animals suspend themselves from their hands and move by swinging from one hold to another.

Binocular vision: Vision in which both eyes can focus together on a distant object to produce three-dimensional images.

Stereoscopic vision: Vision in which three-dimensional images are produced because each eye sends a signal of the visual image to both hemispheres in the brain. Stereoscopic vision requires binocular vision.

Strepsirrhine: Any member of the group containing lemurs and lorises. The system classifying primates into haplorrhines and strepsirrhines is a cladistic alternative to the evolutionary systematic taxonomy, in which primates are divided into prosimians and anthropoids, and tarsiers are grouped with prosimians.

Haplorrhine: Any member of the group containing tarsiers and anthropoid primates. The system that classifies primates into haplorrhines and strepsirrhines is a cladistic alternative to the evolutionary systematic taxonomy, in which primates are divided into prosimians and anthropoids, and tarsiers are grouped with prosimians

Dental Formula: The number of incisors, canines, premolars, and molars on one side of the upper and lower jaws.

Maxilla: The upper jaw.

Mandible: The lower jaw.

Bilaterally symmetrical: In animals, the quality of having the morphology on one side of the body's midline be a mirror image of the morphology on the other side.

Prehensile: Of hands, feet, or tails: capable of grasping objects, such as food items or branches.

Cooperative breeding: A mating system in which there is one breeding female and all group members help care for the offspring.

Basal metabolic rate: The rate of energy use required to maintain life when an animal is at rest.

Secondary compound: A toxic (poisonous) chemical compound produced by a plant and concentrated in the plant's tissues to prevent animals from eating the plant.

Alkaloid: A type of secondary compound produced and kept in a plant's tissues that makes the plant distasteful or even poisonous to herbivores.

Gum: A sticky carbohydrate that some trees produce in response to physical damage. Gum is an important food for many primates.

Frugivore: An animal whose diet consists mostly of fruit.

Folivore: An animal whose diet consists mostly of leaves.

Gummivore: An animal whose diet consists mostly of gum.

Dominance matrix: A square table constructed to keep track of dominance interactions among a group of individuals. Usually, winners are listed down the left side and losers are listed across the top, and the number of times each individual defeats another is entered in the cells of the matrix. Individuals are ordered in the matrix so as to minimize the number of entries below the diagonal. This ordering is then used to construct the dominance hierarchy.

Transitive: A quality of triadic (three-way) relationships such that the relationships between the first and second elements and the second and third elements automatically determine the relationship between the first and third elements. For example, if A is greater than B and B is greater than C, then A is greater than C. In many primate species, dominance relationships are transitive.

Social Organization: The size, age–sex composition, and degree of cohesiveness of primate social groups.

Polygyny: A mating system in which a single male mates with many females. Polygyny is the most common mating system among primate species.

Mating system: The form of courtship, mating, and parenting behavior that characterizes a particular species or population. An example is polygyny.

Polygynandry: A mating system in which both males and females mate with more than one partner of the opposite sex

Derived traits of primates: 

1. Most primates have opposable toes and thumbs that they use for grasping.

2. There are flat nails on the hands and feet in most species, instead of claws, and there are sensitive tactile pads with “fingerprints” on the fingers and toes.

3. Locomotion is hind-limb dominated, meaning that the hind limbs do most of the work, and the center of gravity is nearer to the hind limbs than to the forelimbs.

4. Unspecialized olfactory apparatus that is reduced in diurnal primates 

5. Visual sense is highly developed. The eyes are large and move forward in the head, providing stereoscopic vision 

6. Females have small litters, and gestation and juvenile periods are longer than in other mammals of similar size 

7. The brain is larger than the brains of similarly sized mammals, and it has several unique anatomic features 

8. The molars are relatively unspecialized and max of two incisors, one canine, three premolars, and three molars on each side of lower and upper jaws

9. Several subtle anatomical characteristics that are useful to systematists such as eye orbits that are fully encased in bone but that are difficult to interpret functionally 

platyrrhine 

• Diurnal

• Live in forested areas

• Mainly arboreal 

• Quadrupedal

• Round nostrils 

• Three premolars on each side of upper and lower jaws

• Central and south america and southern mexico 

Catarrhine

• Narrow nostrils face downward 

• Two premolars on each side of upper and lower jaws

• Larger than platyrhine species 

• Occupy larger variety of habitat than platyrrhine 

• Africa and asia

Where Primates Live Today:

• Nonhuman primates do not live in the wild in Australia.

• Living nonhuman primates are primarily located in tropical regions of the world.

Where they don't (not true statements below) 

• Both living and fossil nonhuman primates have been found distributed throughout most parts of Asia.

• Living nonhuman primates inhabit a much wider region than their fossil ancestors did.

• Fossil nonhuman primates were found in more equatorial areas than living nonhuman primates.

Strepsirrhines include the lorises, lemurs, and galagos. Haplorrhines include the tarsiers, monkeys, apes, and humans.

One-male, multifemale social groups are very common among primates and the term "polygyny" is often used as a shorthand describing the mating system in these groups.

An animal’s basal metabolic rate is the energy needed to regulate essential body functions. Energy is also needed to sustain growth, development, and reproduction.

At rest large animals use less energy per unit of body weight 

The dental formula shows how many of each type of tooth a particular species has on one side of its jaw. The dental formula is written like this:

2.1.3.3

—----------

2.1.3.3

Usually, the dental formula is the same in upper and lower jaws of the same species. There are some exceptions, though, such as the tarsier, which has two incisors in the upper jaw and only one in the lower jaw.

Dental formulas are counted from front to back, starting with the incisors. This image shows the mandible of a male colobus monkey. To find the dental formula, start with the incisors and count on one side: two incisors, one canine, two premolars, and three molars, giving a dental formula of 2.1.2.3.

Hylobatidae 

• Smaller body size 

• Pair bonded social groups 

• Strictly arboreal 

Hominidae 

• Arboreal and terrestrial 

• Larger body size 

• Varied social organization or social systems 

Gorillas are in africa 

RIng tailed lemur in madagascar 

Orangutans are found in far Southeast Asia in Sumatra and Borneo.

Howler monkeys are found in south america 

Different between male and female chimps

• Canines 

Same between male and female chimps

• Molars

• Incisors

• Brow ridges 

Extant nonhuman primates live

• South America

• Central America

• Africa

• Asia

Where extant nonhuman primates do not live

• Australia 

Apes and old world have 2.1.2.3 while platyrrhine and new world have 2.1.3.3

The Y-shaped pattern of the molars is found in apes; catarrhine monkeys have parallel ridges on their molars.

The infraorder Lemuriformes includes lemurs,, which are found only in Madagascar and the Comoro Islands off the coast of Africa.

Catarrhines have a 2.1.2.3 dental formula and are generally larger than platyrrhines. Prehensile tails are only found in platyrrhine species.

Territorial primates use vocalizations to announce their presence.

Territorial species aggressively defend the borders of their territories from outsiders.

Nonterritorial primates have home ranges that overlap with those of neighboring primate groups.

• If they mingle together they may interact peacefully, avoid each other, or fight 

Primate Extinction Dangers

• Hatat loss

• Climate change

• Bushmeat trade 

Why Comparative method is used

• The method allows scientists to discern the traits that primates have in common versus the differences that emerge from ecological variation.

• The method provides insight into hominin evolution since there is little evidence of behavior in the fossil record.

Female reproductive strategies/ success 

• lots of parental investment

• importance of longevity

• importance of social bonds

• access to good resources

Male reproductive strategies/ success 

• competition for access to mates

• limited parental involvement

• sexual selection

Counterstrategies against infantacide:

• Females try to confuse male about paternity

• Females try to protect offspring 

Intersexual Selection 

• females choose mates

• attractive traits that indicate quality

• rare among primates

Intrasexual Selection 

• male–male competition

• larger canines

Drive variation in female reproductive performance

• rank

• age

• longevity

• social bonds

Infancticide in baboons and impact on male-female relationships

• Females form friendships with one or two adult males.

• Male friends can intervene on behalf of their female friend and protect the female's young.

• A friendship between a female with offspring and a male does not increase the chances of infanticide.

Intrasexual selection favors traits that increase success in male–male competition.

Sexual selection results in male adaptations that enhance their ability to compete with other males for access to females.

Sexual selection as strong as ordinary selection 

Intersexual selection does not favor traits that increase success in female-female competition 

Groups that consist of multiple males and one female do not always engage in a cooperative breeding system.

• Sometimes one male breeds like in marmoset 

False: he male in one-male, multifemale groups has assured, exclusive access to the females.

• There may be competition with males outside the group who try to gain access to the females.

Sexual dimorphism arises from intrasexual selection.

Hrdy's hypothesis that infanticide is an evolved reproductive strategy has been subject to criticism. Sommer believes that the criticism is the result of "naturalistic fallacy."

• The naturalistic fallacy suggests people believe that if we accept infanticide as "normal" in primate groups, it must also be justified in humans; what is found in nature is "right, just, and inevitable" according to this fallacy.

Why are dominance hierarchies among the females of a primate species formed?

• Females flight over access to food resources 

Most important factor for female primate reproductive success is her ability to obtain nutrient rich resources

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