Primatology

Why study Primates?

Help learn more about our own:

• life history,

• development

• adaptations

What is a Primate

• Look at suites of traits to distinguish

• also look at phylogenetic analysis

• BUT Remember: studies were conducted before the advent of DNA technology

Primate is Linnaean order which include:

• Lemurs

• Monkeys

• anthropoid apes

• humans

What suites we look at to distinguish them?

4 Categories:

• Locomotion

• Feeding

• Neural/sensory

• Life history (developmental)

How do we analyse these traits?

Look through lens of selective pressures which give rise to the traits:

Helps to understand why some traits have evolve

1. LOCOMOTION- selective pressure

Selective pressure created by habitat in which the animal lives

• Tree dwelling: Pressure= climb, swing, hang etc

• Ground dwelling: more time in life walking

2. FEEDING- selective pressure

Diet will affect:

• teeth

• digestive systems

• motor systems to ‘harvest’ food

  • Note: cross over between locomotion and feeding

3. SENSORY SYSTEM- selective pressures

Many and varied:

• Availability and form of food

• sociality

• presence of predators

• existence in complex 3D world

• adaptations to daytime living

All shape evolution of senses and brain

ALSO: shaped by animals life history:

• Human brain uses 20% of our energy

How we know what traits are functionally advantageous?- why difficult

Need to distinguish between traits which are adaptations vs traits which hvae evolved in association with other functional traits

How do we distinguish this?

Use isometric and allometric scaling:

Helps identify specialised adaptations (isometric) rather than ‘by products’ (allometric)

How use isometric and allometric scaling

By product:

• animal grows twice as tall as ancesteor

  • resonable to expect arms and legs to be twice as long

  • = not adaptaion: just by product

Adapatation:

• Find an animal twice as tall but with much LARGER torso and stumpy legs

  • conclude: must be adaptaion rather than scaling byproduct

Other example of scaling byproduct

Brain weight relative to body weight:

• Usually byproduct: large animals = larger brain

  • Generally allometric

• Humans do not fit generalised data: larger brain for body weight

  • Significantly above allometric line

  • THEREFORE = ADAPTATION

Looking at suit of traits:

Brains

Primates larger brains to body sizes:

• Enlarged neocortex (outer layer of brain)

• Humans- very much enlarged neocortex

  • Used for: higher cognitive functions

    • emotions, reasoning, understanding physical world

How compare neocortex size:

• Compare to Medulla (used for involuntary (respiration, heart rate etc)

• Medulla doesn’t really need to be that big?

Social Brain Hypothesis

Selective pressure for enlargement of neocortex is social complexity

• e.g to help know who is who, who is related to who, individual’s rank etc

Ecological Pressure Hypotheses

Larger brains evolved to aid finding food:

• Plot:

• x= amount of fruit in diet or distance to food or food extracting difficulty

• y= Neocortex size

Result:

NO CORRELATION

• only a correlation with group size and neocortex size

Implication on diet: Jarman-Bell Hypothesis

Larger animals generally have lower basal metabolic rates

• get by eating lower-energy food (leaves- gorillas)

Smaller

• Need more energy rich foods (chimp eats fruit)

Jarman-Bell Hypothesis Explanation

Diet acts as a constraint:

• higher energy diets: Permits development of larger brains

• Low energy diet: constraint on energy allocation to the brain

Chimp vs Gorilla

• Relative brain: Chimp = Larger brain (but smaller animal)

• Gorilla bigger brain absolute size: but smaller relative to size of animal

  • N.B not much evidence for omnivores for this!

Life History Traits

Normally among mammals

• Fertility rates, life expectancy etc allometrically allign with body size

Primates:

• Fall below allometric line for fertility

  • reproduce slower than other mammals

• Above for life expecany

• in general: slow life history

  • Longer gestation rates, slower postnatal dev, later ages at first reproduction

Life History related to large brains

Large brains = lots of energy needed to be made

• ‘Growing up’ needs energy

• Trade off in terms of:

  • 1. Energy allocation vs brain developments

  • 2. Parents energy/time vs parents reproduction rates

    • Cannot reproduce much if raising child

    • Evidence: Changes in altriciality (maturity of offspring at birth)

      • e.g Ruffed grouch chicks walk one day old

      • vs Meadowlarks at one day old rely on parents to feed and protect

      • Meadowlarks= ALTRICIAL

      • e.g new born horses to humans- foal can walk after a few hours

Socail consequences of slow life history

Generation length is long:

• get generation overlap

• Allows for:

  • Socialising

  • learning from others

  • building long-term relationships

    • TOOL USE

Sensory Traits

Most primates have:

• increase visual

  • Eyes face forward

  • allow steroscoptic 3D vision

  • accurate depth perception

  • coordinate brain, eyes, hands

Links to

• decrease olfactory

  • Shorter snouts (coz of eyes face forwards)

  • olfaction not needed

  • because can see: do not need smell vision

These two traits work together to promote/ decrease one another

Hypothesis for selective pressures on stereoscoptic vision:

1. Arboreal life hypothesis:

• can gauage precise location of food

• next branch to swing from etc

• need good depth perception

2. Visual Predation Hypothesis:

   • Depth perception needed to locate mobile prey

   • coordinate hand-eye movement

Not mutually exclusive hypothesis

• probably a combination of both!

Morphological traits- Hand based

Hand based

• High degree of prehensility (graping)

  • opposable thumbs

  • HUmans have flexible hands (not all primates)

  • Flexible feet and prehnsible big toes

    • For Arboreal living

    • Humans lost- due to bipedalism

  • Most have them

    • Spidermoneky lost: uses tail as appendage

    • swing through trees (brachiation)- do not need thumb

  • NB: also found in opossums, panda, many marsupial and frogs

• Sensory nerves in fingertips and nails (no claws)

  • enhance coordination and tactility of hands and feet

Morphological traits: Arms and legs

Clavicle:

• highly developed in primates

• Presence high among mammals

  • primates, bats, monotreme highly developed

  • marsupial presnt

  • rodents edentates- rudimentary

  • Not in whales, horses

• How helpful?

  • Mobility of arms and shoulders

  • great range

  • climbing, holding on to trees

  • ALSO: Pre adaptation for tool use

Morphological traits: Teeth

Fewer teeth than many other mammals

• specialisation of molars, premolars, canine, incisors

• reduction in numbers is related to:

  • changes in shape of mouth and face:

    • Due to vision increase

  • Also: Dietary changes

    • Frugivore: different requirements to insecti/carnivore

Co-Evolution hypothesis

• Angiosperms evolve into tropical forests

• become bigger

• Seeds got bigger

• Needed Larger animals to spread seeds

Therefore:

Availability and food type drove evolution of animal traits

and

Animal traits drove evolition of availabiltiy and type of food

• Can see throught evoelution:

  • pollination, predator/prey evoltuion in the Campbrain explosion

  • more examples etc

How primate Order is Structured

500 species, 200 classified in 20 years

Divided into Several Clades:

• Prosimians:

  • Lemurs, loris, galagos

  • Earliest diverging

• Tarsiers: not considerd prosimins any more

  • sister to rest of them

• Platyrrhines (‘flat nose’) (New world)

  • marmosets, capuchins, spider monkey

• Catarrhines (Down pointing nose) (Old world Monkeys)

  • baboons, macaques, colobus

• Lesser ages (gibbons)

• Great Apes (chimps, gorillas, orangutans and humans

Platyrrhines + Catarrhines= Anthropoids

Anthropoids + Tarsiers = Haplorrhines (‘simple nose’ i.e wet-nosed)

Where do most primates live

Subtropical areas with biodiversity hotspots

• Amazon

• Congo basin

• Malaysia/SE Asia

• Madagascar

  

Characteristics of different groups: Prosimians

Note: easy to find exceptations because of selective pressures

Where: Africa and Asia

• Eyes:

  • Reflective layer in eyres

• Size:

  • Small

  • but were large lemurs once

• Olfaction

  • have scent glands

  • use a lot

• Arboreal

  • except ring-tailed lemurs

• Mostly solitary

  • except some lemurs

• Mostly nocturnal

  • Except some lemurs

Note: execptions are with lemurs!

Platyrrhini

Where: America

• Direunal

  • Except Owl Monkeys

• Group living

• Some have Fast reproduction rates e.g Tamarinds

  • Some have cooperative breeding system

    • one dominant couple breeds

    • others look after offssrping

  • Some slow reproduction

    • e.g capuchins, howler/spider monkeys

  • Some, Harems of females to one male polyandry

• Vision

  • Mostly dichromatic 2 colour vision

    • except howler monkeys

• Large brains and tool use

  • Only in Capuchins

Colobines (found in Cercopithecidae)

• Diet: Leaves

  • Specialised stomach

  • sharp molars

• Diurnal

• Live in groups

• Harem mating system

  • One male, several females

• strong sexual dimorphism

  • infanticide common (similar to lions

Cercopithines- (found in Cercopithecidae)

Where: Africa and Asia

• Society

  • Females form coalitions among related females

  • with rank

  • help eachother

• Diet:

  • mostly frugivores

• Mating systems:

  • Vary

  • harems or polyandry

  • sexual swelling to show when females are sexually receptive

    • why?: increaess liklihood dominant males will mate with them

    • and encourage less dominant to mate too

    • result: reducing risk of infanticide

• cheek pouches:

  • store food

  • eat a lot quickly

  • broken down by saliva

  • so can eat when in trees

Lesser apes (gibbons and siamangs)

Where: Tropical Asia

Society:

• live in couples

• territorial

• offsrping disperse

Tail?

• No apes have tails

Locomotion:

• brachiation- swing

Greater apes (orangutans, gorillas, bonobos and chimps)

Orangutangs:

• semisolitary

• young are heavily dependent on parents

Gorillas:

• Harems or polyandrous/polygynous marting systems

Bonobos and Chimps:

• females disperse

• males born in group and stay in group

Notes on comparative approach:

Make sure to remeber homolgies and homoplasia

• Behaviour cannot be fossilised

• BUT: it can be inferred

  • e.g we ssee bone adaptation for biped walking

  • infer walking behaviour

  • e.g shape of teeth= diet behaviour

What comparative biology helps us do

Takes us beyond anthropocentric comparison

Allows us to:

• compare different population of the same species living in different habitat

• identify wehther behaviours respond to different ecological pressures

• OR

• whther species typical pattern in behaviour are a result of evolutionary history

i.e are behaviours due to ecological or evolutionary history?

In summary:

• evo relationships of groups of primates

• some characteristics of the groups

• some evo pressures causing these characteristics

• how we can use fossil evidence to infer behaviour or traits which do not fossilise

Sets the scene for understanding more about the conditions which made it possible for humans to evolve