Unit 5 Primates and Primate Evolution Biology Lecture Notes

Unit 5 – Primates and Primate Evolution – Biology Lecture Notes

I. Introduction

a. Primates are a group of mammals that includes monkeys, apes, and humans.

b. They are atypical as a group in that they follow a generalized form that is not

specialized for any specific adaptive strategy

c. In addition, primates occupy every environmental niche on the planet, from the tropics

to the artic.

II. Primate Evolutional Trends

a. Primates are distinguished by three main evolutionary trends

1) Limbs and Locomotion

i. pentadactyly

ii. nails instead of claws

iii. prehensile hands and feet

iv. ability to maintain erect posture

v. retention of the clavicle

2) Dentition and Diet

i. generalized dental pattern designed for varied diet

ii. omnivorous subsistence pattern

3) Cranio-Neurology and Behavior

i. reduction of snout and de-emphasis of olfactory senses

ii. increased emphasis on vision and stereoscopic vision*

iii. increased complexity of the brain

iv. increased parental investment

v. increased dependency on learned behavior

vi. greater group cohesion

vii. adult males permanently associated with the group

*stereoscopic vision: when visual fields of each eye overlap and

sensory information from each eye is relayed to both sides of the

brain, allowing depth perception & accurate distance estimation

III. Explanations for Primate Evolutionary Trends

a. Arboreal Adaptation Hypothesis

1) The primates adaptation to an arboreal niche is principally responsible for most

of the unique primate evolutionary trends

2) Morphological characteristics such as dentition, diet, locomotory patterns, and

limb architecture are all due in some measure to the adaptation of life in the trees.

3) Physiological characteristics such as increased dependence on vision,

stereoscopic ability, reduction of the snout and de-emphasis on olfactory senses

are due to adaptations to an arboreal existence.

4) Behavioral traits such as omnivorous diet can be seen to take advantage of the

varied forms of food found in the forest canopy.

5) Dental generalization can also be seen to take advantage of the varied dietary

possibilities found in trees.

b. Visual Predation Hypothesis

1) Matt Cartmill has proposed an alternative explanation for the development of

primates unique evolutionary trends

2) This hypothesis is called the Visual Predation hypothesis, and considers that

primates unique adaptations are due to the use of a low forest canopy

niche and a reliance on insects and small fruits for subsistence

3) This hypothesis works well with the smaller primates, but fails to explain the

development of the larger primates, which clearly could not subsist on

small insects and fruit.

IV. Classifying the Extant Primates

a. Primary Classification of Primates within the Animal Kingdom

Kingdom – Animalia (animals)

Sub-Kingdom – Metazoans (multi-celled animals)

Phylum – Chordata (animals with a spinal chord)

Sub-Phylum – Vertebrata (animals with vertebral column)

Class – Mammalia (mammals)

Sub-Class – Eutheria (placental mammals)

Order – Primates

b. Secondary Classification within the Order Primates: This system classifies species

based on traditional taxonomic characteristics.

1) The taxonomic organization of species is hierarchical. Each species

belongs to a genus, each genus belongs to a family, and so on through

order, class, phylum, and kingdom. Associations within the hierarchy

reflect evolutionary relationships, which are deduced typically from

morphological and physiological similarities between species. So, for

example, species in the same genus are more closely related and more

alike than species that are in different genera within the same family.

Sub-Order – Strepsirhini – the Prosimians, including the Lemur and Loris

Sub-Order - Haplorhini – the Anthropoides, including all other primates

Infra-Order Tarsiiformes – the Tarsiers

Infra-Order Platyrrhini – New World Monkeys, including Howler, Spider,

& Marmosets

Infra-Order Catarrhini – Old World Monkeys

Super-Family Cercopithecoidea, including Langurs, Macaques,

and Baboons

Super-Family Hominoidea, including the Lesser and Greater Apes,

and Humans

Family Pongidae

Lesser Apes, including the Gibbons and Simangs

Greater Apes, including Orangutans, Gorillas, and

Chimpanzees

Family Hominidae, including humans and our ancestors

Genus Australopithecus

Species afarensis, africanus, and robustus

Genus Homo

Species habilis, erectus, and sapiens*

*only Homo sapiens are still extant

c. Grades of Primate Evolution: This system classifies species not strictly based on

normal taxonomic characters, but based on behavioral traits. Since primates are so similar

taxonomically, this system may be more useful for the study of primates.

Lower Primates

1) Grade 1 – Tree Shrews. While not classified as true primates, they may

represent an example of the transitional forms that existed about 70 mya, when

primates first emerged from early mammal forms

i. Tree Shrews, who all live in southeast Asia, have claws on all digits, no

stereoscopic vision, no parental investment, but are all arboreal, have

prehensile hands and feet, and have a similar diet to primates

2) Grade 2 – Prosimians (Lemurs, Lorises, and Tarsiers). Lemurs are found only

on the island of Madagascar, and are the only primates on the island. Lorises are

in equatorial Africa and southeast Asia. They exhibit a wide variety of forms,

including nocturnal and diurnal, terrestrial and arboreal, social and solitary. They

all have a rhinarium (wet nose). They may be seen as “living fossils” or links

between the rodent-like Tree Shrews and the anthropoids.

Higher Primates

3) Grade 3 – Monkeys (New and Old World varieties).

New World varieties exist primarily in tropical zones, are all arboreal, platyrrhines

(flat nosed), have prehensile tails, and locomote via brachiation and

quadrupedalism. Types include Marmoset, Tamarin, Squirrel, Capuchin, Howler,

and Spider Monkeys.

Old World varieties exist in every niche not permanently covered in ice, and

quadrupedal and mainly arboreal, but some baboon groups live in terrestrial

savannas and some macaque groups live in a semi-aquatic niche. No prehensile

tails, and many types have an ischial callosite, a special pad on their butts for

sitting long periods. Females have a periodic estrous cycle which limits their

fertility and sexual receptivity. Types include macaques, baboons, langurs, and

mandrills.

4) Grade 4 – Hominoids (Greater and Lesser Apes). Have larger body sizes, lack

a tail, have more complex behaviors and brains, and an increased period of infant

dependency

Lesser Ape varieties include the Gibbon and Siamang, both found in southeast

Asia. They are the smallest of apes, and locomote via brachiation (arm over arm

swinging through the branches)

Greater Ape varieties include Orangutans, Gorillas, Chimpanzees, and Humans

Orangutans (Pongo pygmaeus) live only on the Indonesian islands of Borneo and

Sumatra. Name means “old man of the jungle” in local language, are primarily

arboreal, but can locomote via quadrumanualism (knuckle-walking).

Gorillas (Gorilla gorilla), live in central Africa. They exhibit extreme sexual

dimorphism, with females about 200 lbs, and males over 400 lbs. they locomote

by knuckle-walking, are very social and highly intelligent.

Chimpanzees (Pan troglodytes), live in central Africa, and exhibit moderate

sexual dimorphism, locomote by a modified semi-erect knuckle-walking, are very

social and highly intelligent, even capable of some degree of tool making and

simple language.

Humans (Homo sapiens), live everywhere, and are both a typical and unique

hominoid, about which you will spend a significant portion of the class learning.

V. Fundamentals of Primate Behavior

a. Introduction: Studying nonhuman primate behavior helps us learn more about ourselves, and also may help us to prevent the growing likelihood of extinctions of many primate species.

b. The Evolution of Behavior: Primates are studied within an ecological and evolutionary framework, termed behavioral ecology

1) central to behavioral ecology is the premise that behaviors have evolved through

natural selection

2) behavior is viewed as a flexible, complex trait that is influenced by the interaction

between genes and the environment

3) behavioral ecology is an outgrowth of socioecology and sociobiology

i. socioecology studies the patterns of relationships between the environment and

social behaviors

ii. sociobiology also focuses on the relationship between natural selection and

behavior, but downplays the role of ecological factors

ex. male infanticide: in many primates, including baboons, orangutans,

chimpanzees, and humans, new males come into a group and drive out a dominant

male, then often kill the groups infants. This maximizes the males reproductive

success, allowing his offspring to be predominant.

c. Primate Social Groups. Unlike most other mammals, primates live in permanent social groups

1) as in other mammals, members of one sex disperse at maturity

i. male dispersal is the rule for most primates

ii. females disperse in baboons, chimpanzees, and gorillas

d. Primate Social Behavior.

1) Dominance Hierarchies serve to impose order within groups

i. rank or status is measured by access to resources, which may include access to

preferred mates or the exclusion of other members from those mates

ii. rank changes throughout an individuals lifetime

iii. males are usually dominant to females, with additional hierarchies within

those two groups

2) Communication includes gestures, facial expressions, and vocalizations

i. high-ranking members often express dominance through mounting gestures

ii. submission can be indicated by crouching, touching, presenting the

hindquarters, and grooming, and chimps reassure by holding hands and

hugging

3) Aggressive and Affiliative Strategies are balanced to preserve order.

i. dominance often is expressed through violence

ii. dominant individuals often form subgroups to consolidate power

4) Reproductive Strategies

i. generally, females are receptive to males only while in estrus

ii. a few primates form consortships, where males and females stay bonded

beyond the estrus cycle, include baboons, chimpanzees, and humans

5) Mother and Infant Relationships are the basic social unit in primates

i. the mother-infant relationship is essential to the development of all primates

ii. in higher primates like chimpanzees, both daughters and sons maintain

relationships with their mothers