THE EVOLUTION OF BEHAVIOR

§      Study of behavior in free-ranging primates

§      From “ecological” and “evolutionary” perspective

§      Relationship between:

§    Behaviors

§    The natural  environment

§    Biological traits of species studied

Ecological

§      Relationship between organism and all aspects of environment

§      For example food resources and predators

Behavior

§      May or may not be deliberate

§      Not necessarily the results of conscious decision making.

Behavioral Ecology

§      An approach that focuses on the relationship between behaviors, the natural environment, and biological traits of the species.

§      Some behaviors are influenced by genes

§      Subject to natural selection

Primate Social Structure

§       the results of natural selection in specific habitats.

§      Body size

§      Distribution of resources

§       Predation

Body Size

§    Larger animals require fewer calories by weight than smaller animals.

§    Larger  animals are better able to retain heat

§    Overall energy requirements are less than for smaller animals.

Distribution of Resources

§     Leaves can be abundant will support large groups of animals.

§     Fruits and nuts occur in clumps. These can most efficiently be exploited by smaller groups of animals.

§     Some species that rely on foods distributed in small clumps tend to be protective of resources

Predation

§    Primates are vulnerable to many types of predators

§    Where predation pressure is high, large communities are advantageous.

PRIMATE SOCIAL BEHAVIOR

§      Primates solve major adaptive problems in a “social context”

§      Several behaviors reinforce integrity of group

§      Includes dominance, communication, aggression, affiliation and altruism

§      Many primate societies are organized into dominance hierarchies.

§      These impose a certain degree of order 

Displays

§      communicate emotional states

§      Elaborate, complicated, repetitive

§      Gorilla – chest slapping, tear vegetation as threat display 

Aggression (Against Intrusion)

§     Often to protect individual or group resources

Home Range

§      Primate groups are associated with a home range where they remain permanently

Core Area

§       is portion within home range

§      Contains the highest concentration of predictable resources

§      The core area can also be said to be a group’s territory, and it’s the portion of the home range defended against intrusion.

Affiliation and Altruism

§      Many behaviors minimize violence

§      Reinforce bonds between individuals and enhance group stability

Grooming

§      – pick through fur

§      Social grooming common among primates

§      Reinforces social relationships

Altruism

§      Behaviors that benefit another while posing risk to oneself,

§      Common in primate species

§      Defend another against a predator

§      Adoption of orphans

Patterns of Reproduction

§      In most primate societies, sexual behavior is tied to the female’s reproductive cycle.

§      Mating only when in “estrus” indicating female receptive

Bonding

§      A type of natural selection that operates on one sex, usually males.

§      Long-term, this increases the frequency of traits that lead to greater success in acquiring mates.

Dimorphism

§      Sexual selection produces dimorphism

§      Especially body size

§      Presence or absence of dimorphism can indicate mating structure

MOTHERS, FATHERS AND INFANTS

§      It is learned; it’s passed from generation to generation through learning (not “biological”).

§      Not just applied to humans

§      Term “cultural primatolgy” now used

§      tool use

§      1) “Termite fishing”

§      2) “Leaf sponges”

§      3) Hammerstones and platforms to crack nuts

Regional Variation

§      Only chimp habitually makes and uses tools

§      There are regional variations of tools used

§      Regional dietary preferences also noted for chimps

Closed System

§      It has been assumed t that nonhuman animals use a closed system of communication, where vocalizations don’t include references to specific external phenomena

§      These view now challenged.

Language

§      These views have been challenged:

§    Vervet monkeys use specific vocalizations to refer to particular categories of predators, such as snakes, birds of prey, and leopards.

Vervet Monkeys

§    Vervet monkeys have different alarm calls for particular predators

§    Snakes, eagles, leopards

§    Not involuntary

§    Learned (but limited)

Apes

§      Psychologists (especially working with chimpanzees) report that

§      Apes can learn to interpret visual signs and use them in communication

§      That apes can’t speak has Less to do with intelligence than to:

§      1) anatomy of vocal track 

§      2) language-related structures in the brain

Experiments (primate communication)

§      Attempts to teach chimpanzees to speak failed

§     Experiments with other methods (next)

Washoe

§     Infant chimpanzee

§     Was taught ASL (American Sign Language)

Loulis

§      Enfant placed in Washoe’s care

§      Learned signs taught by Washoe

Sara

§     Chimp

§     Plastic chips recognized as symbols for various objects

Koko

§     Gorilla

§      ASL

§     Learned 500 signs

Chantek

§     Orangutan

Sherman and Austin

§     Chimpanzees

§     Used symbols to categorize “classes” of objects

§     (not just “specific” items)

Lana

§     Chimp

§     Computer keyboard (chips)

Kanzi

§     Bonobo (Chimp)

§      Used symbols (lexigrams)

§     Claimed that young Kanszi began “spontaneously’ acquiring and using symbols

Cenozoic Periods

§       Paleocene (65 m.y.a.)

§       Eocene

§       Oligocene

§       Miocene

§       Pliocene (next chapter)

§       Pleistocene

§      Holocene(Recent)

Levels of Primate Evolution

§       Early Ancestors

§    (placental mammal radiation)

§    Followed by four levels

§       1)  Prosimians

§       2) Anthropoids

§       3) Hominoids

§       4) Hominids

EARLY PRIMATE EVOLUTION

§     Placental mammal radiation 65 m.y.a.

§     During Paleocene

§     Earliest primates diverging

§     Generalized - therefore hard to classify

§      Earliest definite primates appear

§      “the first primates of modern aspect”

§      These fossils found in North America and Europe

§      Continents connected (until Oligocene)

§      Mostly extinct by end of Eocene

Eocene Prosimian Radiation

§      Eocene primates:

§      Some are ancestors of prosimians

§      Such as lemurs and lorises

§      Some are ancestors of tarsiers

Oligocene

§      Numerous fossils of several species of early anthropoids in Oligocene.

§      Most are “Old World Anthropoids”

§      (especially from Fayum)
§      Early Anthropoid radiation in Oligocene
§      Most Oligocene fossils from Fayum, Egypt

New World

§      By early Oligocene continental drift separated the New World (the Americas) from Old World

§      Ancestry of New and Old World forms (“monkeys”) separate after 35 years ago.

§      Suggested that first anthropoids arose in Africa and reach South America by “rafting”

Apidium

§    Small primate

§    Squirrel-sized arboreal quadruped

Aegyptopithecus

§    Spectacular hominoid radiation

§    Diverse Miocene hominoid fossils found in Africa, Asia, Europe

§     “the golden age of hominoids”

§    Many species

§    Much morphological variation

§    None in New World

Miocene Hominoids

§      Diverse

§      Evolutionary relationships often reinterpreted 

§      Hominoids are grouped geographically

§      These hominoids are generalized and primitive

§      Proconsul is best known genus of Early Miocene Hominoid in Africa

§      Especially from East Africa (Kenya)

§      More found in Namibia (southern Africa)  

§      Dryopithecus is best known European genus

§      Sivapithecus is best known genus

Some Conclusions about Miocene Hominoid

§      3) Most too “derived” to be ancestors to living forms

§    (not generalized ancestral form)

§      4) Except  Sivapithecus may link to orangutan

§      5)  Evidence of  “DEFINTE” hominids from the Miocene has not yet been indisputably confirmed

§      However, new finds in Kenya, Ethiopia, and Chad suggest hominids diverged in latter (end of) Miocene (Chad back 7 m.y.a.)

Hominid Divergence

§      Initial divergence of “hominids” from African “hominoids” most likely occurred during late Miocene

§      (there are probable Miocene hominid fossils  (late Miocene)

§      Hominids (family Hominidae) are BIPEDAL

§      First definite Hominid fossils found in Africa

§      Numerous found have been found in Pliocene and first half of the Pleistocene

§      Refer to this period as “Plio-Pleistocene

§      New discoveries show earliest hominids date back to end of Miocene (7-5 m.y,a)

Definition of Hominid

§      Distinctive hominid characteristics 

§     Bipedal locomotion

§     Large brain

§     Tool making (at some stage)

§     These are significant in defining hominids

Mosaic evolution

§      Characteristics did not evolve at same time and place

§      “Mosaic Evolutionary Pattern”  -  physiological and behavioral systems evolve at different rates.

Bipedal Locomotion

§      Walking on two feet

§      Most distinctive feature of family Hominidae

§      Bipedal locomotion is single most important characteristic of hominid evolution indicating if a fossil is a hominid

§      Other features (like brain size and behavior) become significant later

The Bipedal Adaptation

§      Efficient bipedalism as the primary form of locomotion is seen only in hominids.

§      Advantages of bipedalism:

§     Freed the hands for carrying objects and for making and using tools.

§     In the bipedal stance, animals have a wider view of the surrounding countryside.

§     Bipedal walking is an efficient means of covering long distances.

Bipedal Modifications

§      Pelvis most dramatic

§      Shorter, broader, oriented more to sides

§      (basin-like shape)

§      (elongated in quadrupeds)

§      Others modifications:

§      Foramen magnum repositioned

§      Spinal curvature

§      Lengthening of leg

§      Femur angled inward

§      Longitudinal arch

§      Big toe realigned

§      The foramen magnum is repositioned farther underneath the skull

§      Note the more forward position in the human cranium.

Biocultural Evolution

§      Most distinctive human behavioral feature:

§      Dependence of culture

§      Biology makes culture possible

§      Culture further influences biological evolution

Paleoanthropology

§      Paleoanthropology is defined as the study of early humans.

§      Paleoanthropologists reconstruct the anatomy, behavior, and ecology of our ancestors:

§      It is a diverse multidisciplinary pursuit

§      Paleoanthropologists use skills of several disciplines:

§      Geologists, archaeologists, physical anthropologists. Paleoecologists

§      For example

§      Geologists may locate potential early hominid sites

§      “Sites” - locations of discoveries

§      Archaeologists search for hominid trace and study artifacts

§      “Artifacts” are objects or materials made of modified for use by hominids

§     Relative dating determines only whether an object is older or younger than other objects.

§     Chronometric (absolute) dating provides an estimate of age in years based on radioactive decay.

Relative Dating Techniques

§      Stratigrapy - based on the law of superposition, that a lower stratum (layer) is older than a higher stratum.

§      Fluorine analysis applies to buried bones and groundwater seepage. Bones incorporate fluorine during fossilization.

Relative Dating

§      First major category

§      Determines if object is older or younger than other objects

Stratigraphy

§      Layering of deposits

§      Based on the law of superposition,

§      Lower stratum (layer) is older

Fluorine analysis

§      Bones incorporate fluorine from groundwater during fossilization

§      Longer buried - more fluorine

§      Only compare  bones from same location

Biostratigraphy

§      Uses fossils of better known animals to help date associated hominid remains

§      (for example pigs, rodents, baboons)

Paleomagnetism

§      Shifting of the geomagnetic pole

§      Magnetic particles act as ancient compass

§      Point to location of pole when rock formed

Chronometric or Absolute Dating

§      Second major category

§      Provides an estimate of age in actual number of years

§      Most  are “radiometric”

§      Based on rate of radioactive decay

§      Elements disintegrate form another element

Potassium/argon (K/Ar)

§      Potassium decays into argon gas

§      Heating “resets” clock

§      Volcanic rock in East Africa

§      (dates rock - not bone)

§      (used for old events to age of earth)

Carbon-14

§      Radiometric method

§      (commonly used by archeologists).

§      Dates organic material (bone, wood)

§      From few hundred to 40,000 years (or 75,000)

§      Relevant for latter stages of hominid evolution

§      (such as Neandertals and modern humans)

Fission-Track

§      Counts tracks left in crystalline rocks

§      as uranium atoms disintegrate

Regions

§      The three regions where early hominid fossils found

§      Central Africa

§      East Africa

§      South Africa

§      In conclusion of chapter fossils divided:

§      Set I   Basal/pre-australopithecus

§      Set II Australopithecines

§    A. earlier primitive species

§    B. later, more  derived species

§      Set III Early Homo

Sets of Plio-Pleistocene Hominids (with some late Miocene)

§      Numerous hominid fossils

§      First found in South Africa

§      But focus shifted to East Africa

§      Especially Rift Valley

§    Ethiopia, Kenya, Tanzania

East African Rift Valley

§      Geological feature

§      (mountain building, faulting, volcanic activity)

§      Erosion exposes fossils

§      Volcanic material good for dating

South Africa

§      Fossils embedded in rock material

§      Dating difficult

Central Africa

§      Now discoveries in Central Africa (since 2002) are earliest

§      See Chad below

EARLIEST TRACES: PRE-AUSTRALOPITHECUS FINDS

§      Earliest remains classified as “hominids”

§      Starting around 7 m.y.a.

Chad (Central Africa)

§      Nearly complete cranium

Sahelanthropus tchadensis

§      Oldest (“basal”) hominid (if proven)

§      About 7 m.y.a.

§      (Late Miocene)

§      Cranium but no postcranial bones

Orrorin tugenensis

§      Genus assigned to Tugen Hills fossils

§      About 6 m.y.a

§      (“basal Hominid”)

§      “Hominid” because bipedal

Aramis

§    E. Africa, Ethiopia, Afar Triangle

§    Large “collection” of hominid fossils

§    Evidence of bipedalism

Ardipithecus ramidus

§      Genus assigned early Aramis fossils

§      A “basal hominid”
§      Bipedal

§      Well-known, widely distributed, and diverse

§      Found in South, Central and East  Africa

§      Genus ”australopithecus”

§       with several species (maybe 8)

Set II   Australopithecus

§      In summary end of chapter described as “Set II”

§      Includes:

§         A. Early primitive forms

§         B. Later more derived

Australopithecus common features

§      Clearly bipedal

§      Relatively small brains

§      Large teeth

Australopithecus: East Africa

§      More complete remains found  at famous East African sites:

§      Hadar – the “Lucy” skeleton

§      Laetoli - footprints

§      These belong to “Australopithecus afarensis”

§      E. Africa, Ethiopia  (Afar Triangle)

§      Dating -  3.9 and 2.3 m.y.a.

§      Finds include:

§      1) Lucy

§      2) Group of bones of 13 individuals

§      3) Stone tools may be 2.5 million years

§      (oldest cultural evidence yet found)

Laetoli

§      East Africa
§      Fossilized hominid footprints in volcanic ash 

§      Bipedal

Australopithecus afarensis

§      Laetoli and Hadar

§      More “primitive”  (less evolved)

§      than later australopithecines

Koobi Fora

(Lake Turkana)

Olduvai Gorge

§      E. Africa, Tanzania

§      Deep ravine 25 miles long

§      Two million years geological, paleontological sequence  

§      Louis and Mary Leakey conducted continuous

§      Gorge Includes

§      Australopithecines

§      Early Homo

SET III EARLY HOMO

§      The first of our genus “Homo”

§      But distinctively a different hominid genus

§      A Plio-Pleistocene hominid with a larger brain

Homo habilis

§      In  “Early Homo” category

§      Discovered at Olduvai gorge

§      Named “habilis”  (handyman) tools

§      Brain larger

§      Claimed to be early Olduvai toolmakers
§      By using name “Homo” it is argued that
§      Homo habilis was tool maker at Olduvai
§      And a second separate branch of  hominid evolution in the Plio-Pliestocene
§      And probable ancestor leading to Homo sapiens
§      Living at same time as a late line of Australopithecus

Early Homo

§      Evolving into one or more species

§      (like H. habilis and H. rudolfensis)

SOUTH AFRICAN HOMINID

§      In early 20^th century paleoanthropologists considered Asia as likely origin of human family 

§      Also Europe considered a center of human evolution

§      No one paid attention to Darwin’s suggestion that it was more probable that our early progenitors lived in Africa

South Africa

§     South Africa becomes important in history of  hominid discoveries

§      The first australopithecine “the missing link” between apes and humans was discovered at a quarry at Taung

§      The “first” discovered. Not the “earliest”

 More Finds in South Africa

§      As the number of discoveries accumulated, it became clear that the australopithecines were not simply aberrant apes.

§      South Africa (quarry at Taung)

§      First australopithecine discovered

§      or “the missing link” by Raymond Dart. 1924

§      Foramen magnum forward under the skull

§      Upright walking indicated but had small brain

§      Named “Australopithecus africanus”

§      Dart’s report rejected

Australopithecus africanus

§      South Africa

§      Taung and other sites

Further Discoveries of South African Hominids

§      Australopithicines found at:

§    Sterkfontein

§    Drimolen

§    Swartkrans

Review of Hominids from South Africa

§      Remains of 200 individuals

§      Most from nine caves

§      (limestone areas - no volcanic material)

§      Fossil divided into “robust” and “gracile”

Two General Groups

§      Two varieties Australopithecus are recognized

§      Robust
§      Gracile

Note on Set and Subsets

§       Recall that the Australopithecus is “Set II” of the hominids

§      The “Robust” and “Gracile”  types noted above are part of Subset B which are considered “later and more derived”

§      As compared to Subset A which were the first “early primitive” primitive Australopithecus (like A. afarensis)

“Robust”  Australopithecines (South Africa)

Definition

§      Variety (similar to some in East Africa) §      Small brains §      Broad, heavier face §      Very large premolars robust teeth   §      Sagittal crest related to jaw muscles §      Concentrated on heavier vegetable foods §      (specialized on seeds and nuts)