Biological Anthropology Exam #2

Ancestral traits

Features primates share with other placental mammals

Ancestral traits: mammary glands

Produce milk to nourish young

Ancestral traits: homeothermy

Fur for insulation, sweat glands

Ancestral traits: heterodonty

Incisors, canines, premolars, molars

Other ancestral traits

• Expansion of the neocortex

• Placenta, long gestation followed by live birth

• Maternal care of their young

Derived homologies/traits: petrosal bulla

• The one trait that characterizes all primates, to the exclusion of all other mammals

• Bony shell that encloses and protects part of the middle ear, and separates it from the interior of the skull

Derived homologies/traits: grasping hands and feet

Primates have evolved a high degree of grasping ability in the hand and foot

Grasping ability: opposable thumbs and “big” toe

• Primates have 5 digits in their hands and feet (ANCESTRAL HOMOLOGY)

• Opposable thumb: thumb can rotate so that the terminal pad of the thumb comes into contact with the terminal pad of one or more of the other digits

• Opposable big toe: all primates have a big toe that is splayed laterally, away from the other four toes, but humans are the exception

  • Allowed ancestral primates a steady anchor while reaching out to catch an insect

Grasping ability: nails instead of claws

• Seen in all primates except some NW monkeys

• Allows for more dexterity in grasping

Grasping ability: sensitive tactile pads

• Skin ridges on the tips of the digits

• Act to reduce slippage on arboreal supports

Derived homologies/traits: reduced reliance on olfaction (smell)

• Smell—or olfaction—plays a critical role in detection of predators or prey; however, smell is relatively less important in the trees

• Shared derived trait

• Particularly in haplorhines

Reduced reliance on olfaction (smell): olfactory regions of the brain are reduced

• Olfactory bulb: responsible for the perception of odors/smells - reduced in size in primates

• Haplorhine primates have a significantly higher percentage of pseudogenes among the olfactory receptor gene family than do other mammals

• Olfactory pseudogenes: genetic basis for some of this reduction in olfaction in primates

Reduced reliance on olfaction (smell): nasal structures of the skull are reduced

• Nasal structures of the skull are reduced in size

• General shortening of the snout

Reduced reliance on olfaction (smell): haplorhines lack a moist naked rhinarium area surrounding the nostrils

• The rhinarium is very useful to animals with a good sense of smell because it acts as a wind direction detector

•  Lost in haplorhine primates

  
  

Derived homologies/traits: enhanced visual sense

• Stereoscopic vision and enhanced depth perception

• Increased reliance on vision

• Haplorhines have evolved trichromatic color vision

Stereoscopic vision

• All primates can see in three dimensions

• Primate eyes lie in the front of the face

• Binocular vision (overlapping fields of view)

  • Binocular vision is not the same as stereoscopic vision (allows for depth perception)

• In primates, each half of the brain takes in and processes information from the entire visual world on opposite side - not just the opposite eyeball

• Enhanced depth perception

Color vision

• Monochromatic vision: black and white

• Dichromatic vision: only blues and greens

• Trichromatic vision: blues, greens, and reds

• Rods: differences in light intensity, black, white, grey

• Cones: contain pigments (opsins)

  • Most mammals have only two opsins - dichromatic

• See ripe fruits

Postorbital bar

• Primates have forward-facing eyes with an enclosed bony orbit (postorbital bar)

• Postorbital bar: supports the eye on the side

• Postorbital plate: behind the eye

Diurnal

Day active

Derived homologies/traits: large brain

• Large brain relative to body size

• Expanded neocortex

Derived homologies/traits: prolonged life history, single offspring

• Give birth to single offspring, with some exceptions and invest heavily in them

• Longer gestation

• Longer infancy and juvenile periods, and delayed reproductive maturation

• Long lifespan

Primates are social

• Learn from group mates: one reason for that long childhood

• Maintain close social bonds

Carnivores teeth

High-pointed cusps for tearing meat

Many herbivores teeth

Broad flat surfaces on cheek teeth for chewing tough grasses and plant materials

Primate teeth

Low, rounded cusps; generalized dentition that allows them to process most types of food

Generalized features of the primate dentition (i.e., features shared with other mammals)

• Teeth in the upper and lower jaw

• Bilaterally symmetric

• Heterodont dentition (incisors, canines, premolars and molars)

Catarrhine teeth

2.1.2.3

• 2 incisors: cut food

• 1 canine tooth: tear food, also behavioral functions

• 2 premolars and 3 molars: crushing and grinding

Types of teeth

• Anterior teeth: ingestion

  • 2 incisors and 1 canine

• Posterior teeth: chewing

  • Premolars and molars

Insectivory

• Insect-eating

• Sharp crests for puncturing the outer skeleton of insects

Folivory

• Leaf-eating

• Well-developed shearing crests for cutting tough leafy material into small pieces

Folivore-frugivore

Frugivory

• Fruit-eating

• Low cusps for crushing soft fruits

Suborder Strepsirhini

• Superfamily Lemuroidea

  • Lemurs, aye-aye, sifaka

• Superfamily Lorisoidea

  • Lorises, galagos (bush babies)

• Were the first modern group of primates to diverge from early ancestral primates

Suborder Haplorhini

• Superfamily Tarsioidea

  • Tarsiers

• Superfamily Ceboidea

  • Monkeys of Central and South America

• Superfamily Cercopithecoidea

  • Monkeys of Africa and Eurasia

• Superfamily Hominoidea

  • Gibbons, great apes, humans

• Include catarrhines and platyrrhines

Cladogram

Every line but the bottom line is haplorhines

Ancestral mammalian traits of Strepsirhines

• Sense of smell is well-developed

  • Retain the rhinarium

• Lower jaw (mandible) is not fused

• Eye has a tapetum lucidum

  • Most are nocturnal

  • Improves vision in low-light conditions, but at the expense of visual acuity (sharpness of vision, or ability to resolve fine details)

Strepsirhines derived traits

• Grooming claw on 2^nd digit of hind limb

• Tooth comb

  • Together, the grooming claw and tooth comb appear to have evolved as a grooming package

• Postorbital bar

Strepsirhini: Infraorder lorisiformes

• Lorisoidea - Galagos & Lorises

  • Africa and Asia

• Nocturnal

• Varied diets (fruits, flowers, leaves, gums, insects, small mammals & birds)

• Many show: 

  • Solitary foraging

  • Infant parking

  • Many species give birth to either singletons or twins, and some species give birth twice per year

Strepsirhini, lorisiformes: Galagos

• Bushbabies

• Africa

• Known for their leaping abilities – Vertical Clinging & Leaping

• Solitary foragers

Strepsirhini, lorisiformes: loris, potto

• Africa and Asia

• Slow quadrupedal locomotion; reduced 2^nd digits, strong, wide grasp

Strepsirhini, lemuroidea: lemurs

• Madagascar

• Extremely diverse, representing ~ 25% of all extant primate genera

• Vertical clinging and leaping

  • Long powerful hind limbs

  • Long flexible back

  • Long fingers for grasping supports when they land

Strepsirhini, daubentonia: aye-aye

• Diet specialized for wood-boring insect larvae

• Except for thumb and big toe, all digits have claws; elongated and thin 3^rd digit, functions like a skewer

• Large continuously growing incisors

Prosimians

Strepsirhines + Tarsiers

Anthropoids

Monkeys and apes

Haplorhines: Tarsiers, Monkeys, Apes, Humans

• Central and South America, Africa, Asia, and Europe

Derived traits of Anthropoids:

• Most are diurnal 

  • Lack the tapetum lucidum

• Reduced olfaction, enhanced vision

  • Lack the rhinarium

  • Eyes more forward-facing

• Full postorbital closure

• Lower jaw is fused in most

• Larger relative brain size

• Longer developmental periods

• Increased social complexity

Haplorhini, Tarsioidea - Tarsiers

• SE Asia

• ‘Prosimian’ traits (i.e., strepsirhine-like):

  •  Grooming claw

  •  Unfused lower jaw

  •  Nocturnal, Small social groups

• Haplorhine traits:

  •  Lack: tapetum lucidum, rhinarium, tooth comb

• Other derived traits:

  • Adaptations for vertical clinging & leaping

  •  Large eyes relative to body size, orbit anatomy

  •  Nocturnal predators of small vertebrates

Quadrupedalism (Terrestrial or Arboreal)

•  Hind limbs and forelimbs of near equal length

•  Arboreal species have long tails to aid in balance on top of branches

•  Shoulder blade positioned to the side of the ribcage

  Platyrrhines (‘flat-nosed’; Central/South America)

• Broad nose, with outward-facing nostrils

• Smaller body size

• 3 premolars in each quadrant (2.1.3.3)

• All are arboreal

• Some, but not all, have prehensile tail

• Most have 2 color vision

• Some have prehensile tail

Catarrhines (‘down-nose’; Africa/Asia)

• Narrow nose, downward-facing nostrils

• Larger body size

• 2 premolars in each quadrant (2.1.2.3)

• Arboreal & terrestrial

• None have prehensile tails

• All have 3 color (trichromatic) vision

• Ischial callosities

Haplorhini, Anthropoidea, Platyrrhini: Marmosets, Tamarins

• Anthropoidea;  C. & S. America

• Callitrichidae: Marmosets, tamarins, Goeldi’s Monkey

• Small bodied (< 1kg)

• Omnivorous, insects & plant exudates

• Variety of social grouping patterns:

  • Usually only one breeding female

  • Intense female-female competition, with suppressed ovulation in subordinate females

  • Twinning is common

  • Males are principal caregivers

Haplorhini, Anthropoidea, Platyrrhini: other monkeys, family cebidae

• Diverse group; taxonomy debated

• Insectivore-frugivores

• Diverse social organization – monogamy (night monkeys) to multimale-multifemale

• Capuchins: Tool use; large brains, slow life histories

• Golden-faced saki: Dental specializations for eating hard nuts (seed predators)

• Night monkey: The only nocturnal monkeys; Monogamy

• Spider monkey: Prehensile tails; highly suspensory

Haplorhini, Anthropoidea, Catarrhini: Cercopithecoidea

• Africa, Asia

• Colobine monkeys

  • Dietary specialist on mature leaves

  • Arboreal quadrupeds; also adaptations for leaping

• Cercopithecine monkeys

  • Arboreal & semiterrestrial species

  • Dietary omnivores

  • Cheek pouches

  • Sexual swelling (bright red butts)

    • Ischial callosities in all

Haplorhini, Anthropoidea, Catarrhini: Hominids

• Apes and humans

• Loss of the tail

• Relatively large brains and enhanced cognition

• Prolonged development

• Postcranial adaptations for suspensory posture and locomotion

Hominids: Suspensory (incl. brachiation)

• Short hindlimbs, elongated forelimbs

• Mobile shoulder joint 

• Shoulder blade located on the back

• Long and curved fingers for grasping branches

Hominids: Gibbons and Siamangs

• Tropical forests of SE Asia

• Smallest of the apes (“lesser apes”)

• Diets focus on fruits

• Socially monogamous

• No sexual dimorphism

• Brachiation

Hominids: Brachiation

Haplorhini, Hominoids: Great Apes

• (Family Hominidae: Orangutans, Gorillas, Chimpanzees, Humans)

• Borneo & Sumatra (Orangutans); Central & West Africa (Gorillas, Chimpanzees)

• Large body size (‘Great Apes’)

• Show suspensory adaptations, but are quadrupedal on the ground

Knuckle-walking

• African great apes

• Form of quadrupedalism practiced by great apes

• Wrist joints are stabilized

Haplorhini, Hominoids, Great Apes: Orangutan

• Genus Pongo

• Male adult:  ~80 kg

• Female adult:  ~36 kg

• Highly frugivorous

• Females are solitary, with dependent offspring

Haplorhini, Hominoids, Great Apes: Gorilla

• Genus Gorilla

• Male adult:  162-170 kg

• Female adult:  71-95 kg

• Folivore-frugivores

• One-male & multimale groups with multifemale females and dependent offspring

Haplorhini, Hominoids, Great Apes: Chimpanzee & Bonobo

• Genus Pan

• Male adult, Chimps:  43-59 kg

• Female adult:  34-46 kg

• Diverse diet, mainly fruit; bonobos more folivorous

• Multi-male, fission/fusion; female bonds important in bonobos

• Tool use & hunting

Major threats

• Nearly half of the world’s primate taxa are classified as Threatened, and in danger of going extinct

• Habitat loss, fragmentation, modification

• Hunting for bushmeat, pet trade

• Disease

• Political instability

• Climate change

Primate diets

• Primates obtain nutrients from many different sources

  • Carbohydrates from fruit and gums

  • Fats and oils from animal prey such as insects, also nuts and seeds

  • Protein from insect and animal prey, and young leaves

• Leaves are also high in fiber, which can be difficult to digest

  • Most colobines eat leaves and have enlarged large intestines

• Insectivores tend to be smaller in body size

  • Smaller animals have relatively higher energy requirements, and eat small amounts of high-quality foods

• Folivores tend to be larger in body size

  • Can afford to eat large quantities of lower-quality foods

Diets influence ranging patterns

• Leaves are more abundant in supply, and predictable in space and time

• Fruits tend to be less predictable in supply, and patchily distributed in space and time

• Folivores tend to have smaller home ranges than frugivores

Why do primates live in groups

• Costs of sociality:

  • Greater competition for resources

  • Vulnerability to infectious disease

• Two main benefits of sociality:

  • Enhanced access to resources

  • Reduced vulnerability to predation

Resource defense model

• Primates live in groups because groups are more successful in defending access to resources than lone individuals

• Joint defense of food resources is profitable when:

  • (1) food items are relatively valuable

  • (2) food sources are clumped in space and time

  • (3) there is enough food within defended patches to meet the needs of several individuals

• Fruit often meets these three requirements

• Thus, between-group competition over food resources favors group living

• Problems of group living:

  • Benefits gained in between-group competition are offset by costs from within-group competition

• RDM doesn’t explain why folivores live in large groups

Predator defense model

• Group living evolved as a defense against predators

• Terrestrial species tend to form larger groups than arboreal species

• Solitary haplorhines (e.g., orangutans, spider monkeys) are large in body size and apparently face little danger from predators

• Juveniles suffer higher mortality in smaller groups than in larger groups 

• Primates seem to adjust their behavior in response to the risk of predation (e.g., alarm calling)

• Weaknesses of the model: predation is very difficult to observe, and it is, therefore, difficult to establish whether it is linked to group size

Reproductive asymmetry

• Primate mothers are almost always the primary (if not exclusive) caretakers of offspring

• The behavior of fathers is much more variable

Reproductive potential

The maximum number of offspring an individual can produce

• Female productive potential is more limited

• Male reproductive potential is very high

Reproductive asymmetry: female strategies

• Females can improve likelihood of offspring’s survival in 2 ways:

  1. Invest more care & energy into offspring  - requires food and other resources

  2. Be choosy about males fathering offspring only mate with quality males

• Female strategies are heavily influenced by the distribution of food in environment

Female strategies: scramble competition

• When resources cannot be easily monopolized

• First-come, first-served basis

  • Resources are of low value, highly dispersed, or occur in large patches

Female strategies: contest competition

• Occurs when access to a resource can be monopolized 

• Some individuals exclude others, and obtain more of the resources

  • Resources patches are clumped, of intermediate size and high value

Dominance

• Often measured as direction of approach-retreat interactions, or the direction of submissive and aggressive behaviors

• When there is contest competition, dominance rank may determine priority of access to preferred resources, increase reproductive success of high ranking individuals

Reproductive asymmetry: male strategies

• High variance in reproductive success

• Limited by access to females

  • Leads to competition among males for mates

• Males can up reproductive success by the number of mates

  • They do this through ‘competition’ with other males to gain access to mates

• All of nothing

Reproductive asymmetry strategies

• Female reproductive success is limited primarily by access to important resources necessary for survival

  • Female strategies are primarily influenced by the distribution of food

• Male reproductive success is limited primarily by the availability of mating opportunities

  • Male strategies are primarily influenced by the distribution of fertile females

Paleontology

The study of extinct organisms based on their fossilized remains

Fertile females: clumped

• Monopolization of fertilizations possible

• One male group

Fertile females: dispersed

• Female dispersed or synchronous breeders

• Difficult to guard and monopolize

• Pair bonds, multiple groups

Appeal to nature fallacy

• Just because something happens in nature doesn’t mean it’s desirable, ethical, or unavoidable

• Observations of primate behavior are not valid justifications for reprehensible human behavior

Social organization

• Female versus Male philopatry

• In female philopatric groups, related females tend to have high degree of affiliation and territorial defense

• Solitary

• Pair living

• Group Living

  • Single Male -  Multi Female

  • Single Female - Multi Male

  • Multi Male - Multi Female

Mating system

• Different from social organization

• Monogamy

• Polygyny: male has multiple female partners

• Polyandry: female has multiple male partners

• Polygynandry: both male and females have multiple partners

Solitary

• Orangutan social structure strongly tied to erratic food supply

• Females live with their offspring; males are solitary

Monogamous pairs

• Little sexual selection

• Males do not invest much energy in courtship or mating

• Males invest heavily in their offspring and in maintaining long-term bonds with their mates

• E.g. gibbons and platyrrhines

One-male, multifemale groups

• Males compete actively to establish residence in groups of females

• Resident males face constant pressure from nonresident bachelor males; threat of aggression

• E.g. Hamadryas baboons

Multimale, multifemale groups

• Larger groups of females; one single male cannot monopolize access to all of them

  • Male-male competition is mediated though dominance relationships

• Male dominance rank is associated with reproductive success in many studies

• Female preferences can influence male mating success

• E.g. chimps

Sexual selection

• A form of natural selection that occurs when individuals differ in their ability to compete with others for mates or to attract members of the opposite sex

• Favors the evolution of traits that allow the limited sex (males in most species) to compete more effectively for access to the limiting sex (females)

Sexual selection: Darwin

Differences in reproductive success caused by competition over mates = sexual selection

Sexual selection: intersexual selection

• Where individuals exert choice among individuals of the opposite sex for mating partners 

  • Favors traits that make males (usually) more attractive to females

• Favors traits that:

  1. Provide direct benefits to their mates 

  2. Indicate good genes and thus increase the fitness of the offspring

  3. Make males more conspicuous to females (although they can be maladaptive)

Sexual dimorphism

When males and females differ consistently in size or appearance

• Greatest in one-male, multifemale (polygynous) social groups

  • E.g. gorrillas

• Least in monogamous social groups

  • E.g. gibbons

Human sexual dimorphism

• Humans have relatively low sexual dimorphism

• Differences in average height of males and females have been explained in problematic ways

  • Recent research has offered an alternative explanation for sex differences in human height:

    • Estrogen in skeletal growth

Sexual selection: intrasexual selection

• Competition among same-sex individuals for access to members of the opposite sex

  • Favors large body size, large canine teeth, and other traits that enhance competitive ability

Intrasexual selection: contest competition

• Contest competition for mates - traits that improve fighting success

  • Body size sexual dimorphism and canine dimorphism

Intrasexual selection: sperm competition

• In social systems where multiple males have access and male-male competition is high, sexual selection favors sperm competition

  • Increased sperm production (testes size)

Intrasexual selection: infanticide

• Act of killing a dependent infant

• One male groups most common

• Outsider males overthrow the resident dominant male, and a new leader male is established

• This may be followed by killing of unweaned infants by the new leader male

Human mate choice

• Humans are sometimes socially monogamous (sometimes serial monogamy)

• Many human societies have different mating systems (monogamous, polygynous, polyandrous…serial monogamy, etc)

• Humans choose mates on the basis of many factors, but some of them may be rooted on our evolutionary past

• Symmetry: honest indicator of the quality of someone’s genes

• Honest signal: information increases the fitness of the receiver

• Some evidence that humans select mates on the basis of odor cues, which indicate genetic diversity at important immune function loci

Major histocompatibility complex

• Proteins that allow immune system to detect foreign invaders

• Greater genetic diversity in MHC may allow for more robust immune response

Primates choose mates based on major histocompatibility complex (MHC) diversity

• Rhesus macaques

  • Males that were heterozygous at a MHC locus sired significantly more offspring than homozygous males increased fitness

• Pig-tailed macaques

  • Similarity in MHC antigens between mother and father predicts pregnancy loss

Behavior is shaped by natural selection

• Violent gorillas that commit infanticide have more offspring than peaceful gorillas that don’t → offspring inherit disposition to violent behavior → infanticide can evolve

• Dedicated marmosets that invest in parental care have more successful offspring that indifferent marmosets that don’t → stable bonds and male parental care will evolve

Human evolution didn’t stop in the Pleistocene

• Humans continue to evolve

• We are not “stuck in the past” any more than other species are

Evolutionary psychology

• A field of study that investigates evolutionary origins of modern human behavior

• Many of these studies don’t consider non-western people

• Some people (academics and non-academics) have used studies of primate behavior to uphold harmful stereotypes applied to humans 

• Beware justifications of bad behavior based on so-called “human universals”