Biological Anthropology Exam #3

We are hominins

Most scientists now use the term hominin to refer to modern humans and their direct ancestors, and hominid to refer to all of the great apes

Divergence and the last common ancestor

• Use comparative method

• Fossil record of modern apes is very poor

  • Lack of fossil evidence likely reflects habitat differences

• Molecular evidence indicates that the divergence between the human and chimpanzee lineage occurred approximately 6-8 million years ago

Gene regulation

Indicates that differences between humans and the apes are more likely due to changes in gene regulation than the structural genes themselves

Evolutionary novelites of humans

•  Habitual upright walking (bipedalism)

•  Characteristics of the dentition 

•  Elaboration of material culture

•  Significant increase in brain size

•  Long developmental period and long lifespan

Mosaic evolution

Different traits evolve at different points in time

Dentition

• 2.1.2.3 dental formula (same as in all Catarrhines)

• Y-5 lower molar pattern

Canine reduction

• Canine size and shape are associated with behavioral differences in apes

• Reduction of sexual dimorphism in hominins → less male-male competition → different social interactions

Canine in apes

• 3rd Premolar (CP₃) honing complex of apes

• When the mouth is closed, the large canines interlock, each fitting into a space, called a diastema, in the tooth row of the opposite jaw

  • In the upper jaw, the diastema is in front of the canine, while in the lower jaw it is behind the canine

• The lower premolar is larger than the premolar behind it

  • Has a single enlarged cusp

  • Its anterior or front surface is smooth and elongated, and it presents a sharpening edge for the canine

• The 3^rd premolar is often referred to as a sectorial premolar

  • Sectorial = adapted for cutting

• Back surface of the upper canine is sharpened, or honed, against the blade-like 3^rd premola

Canine size & sexual dimorphism

• All great apes show sexual dimorphism in the canines

• Great ape males engage in significant competition, often involving physical aggression, with other males over access to females

Ape vs. human dental arcade

• Dental arcade = shape of the tooth row

• Apes:

  • U-shaped dental arcade

  • Large canines, broad incisors

  • Diastema

• Human:

  • Parabolic dental arcade

  • Smaller anterior teeth

  • No diastema

  • Dental reduction

Dentition: prognathism

• Refers to the degree that the face projects forward, in front of the brain case

• Chimps:

  • More facial prognathism

• Humans:

  • Less facial prognathism

  • Small, shorter mandible

Muscles of mastication (chewing): temporalis

• Extends from its origin on the vault of the cranium, passes behind the cheek bone (or zygomatic arch), inserts onto the top of the mandible near the jaw joint

  • Functions in closing the jaw

• Smaller in modern humans

Muscles of mastication (chewing): masseter

• Extends from the cheek bone to the bottom of the mandible

  • Functions in moving the jaw forward, and side to side

• Smaller in modern humans

Apes skull and muscles of mastication (chewing)

• Sagittal crest

• Robust, flaring zygomatic bone

  • In modern humans, with small chewing muscles, the zygomatic is slender and not flaring

• Temporalis

  • In gorillas, this muscle is very large, while the brain case is relatively small

• Masseter

  • Masseter is enlarged, to accommodate high chewing force

  • Arises on the zygomatic arch and insets on the mandible

• Modern human reduction in chewing muscles

Human bipedalism exceptionalism

Humans are the only primates – the only mammals – that do this all the time

Anatomy of bipedalism

• Suspensory locomotion & vertical climbing

  • Increased mobility of extremities

  • Shoulder blade located on back

  • Forelimbs elongated compared to hindlimbs 

  • Long and curved fingers for grasping branches

• Knuckle-walking

  • Wrist joints are stabilized

• African apes have long upper limbs  (inherited from an ancestor with suspensory locomotion)

• Dorsal position of the shoulder blade

• Humans have dorsally positioned shoulder blades as well

Center of gravity

• Fixed point, through which body weight is transmitted or balanced

• When humans stand, the center of gravity is situated directly in the midline

• Only minimal muscle activity is needed to maintain standing posture

Foremen magnum position

• Positioned directly underneath the skull in humans

Body proportions

• Intermembral index = [forelimb / hindlimb] x 100%

• Chimpanzee ~ 110%

• Human ~ 70%

  • Increased stride length

Vertebral column in modern humans

• Cervical (neck) and lumbar (lower back) curvatures to maintain center of gravity over the pelvis

• Larger size of the lumbar vertebrae to support body weight

Pelvis shape in modern humans

• Wide, basin-shaped pelvis

• Short, broad, curved iliac blades

• Medial rotation of the ilium in humans

• Repositioning of the gluteal muscles → Improved lateral stability during swing phase of bipedal walking

Modern human knee

• Valgus angle of the knee

• When humans walk, the foot falls directly below the center of gravity

• Femur is oriented at an angle

Modern human feet

• Big toe is not opposed to the other four digits, and is enlarged in size

• Enlarged heel (calcaneus)

• Development of arches

Adaptive explanations for the origin of bipedalism: social factors

• Ability to provision for the family in the context of the evolution of monogamous systems

  • Carrying tools, food, or infants

  • Provisioning family

Adaptive explanations for the origin of bipedalism: ecological factors

• Moving across forested patches with higher energetic efficiency

• Finding food and spotting predators

Primate evolution timeline

Miocene

• Age of apes

• Earliest human ancestors

Oligocene

Anthropoids (parapithecids, propliopithecids)

Eocene

Earliest definite primates (adapids, omomyids)

Paleocene

Possible primate ancestors (plesiadapiforms)

Timeline

• Between 7-4.4 million years ago, we have evidence in the fossil record of a small number of candidate species

  • Ardipithecus ramidus, Ar. kadabba, Orrorin tugenensis, and Sahelanthropus tchadensis

Geographical location of possible hominins

• Early hominin fossil localities are primarily from east and south Africa

• Nearly all fossil evidence from the first 4 million years of human evolution (7-3ma) comes from East Africa, from a region known as the Great Rift Valley

• S. tchadensis

  • Chad

  • 7-5.2 Ma

• O. tugenensis

  • Kenya

  • 6 Ma

• A. ramidus

  • Ethiopia

  • 4.4 Ma

• A. kaddaba

  • Ethiopia

  • 5.8-5.2 Ma

East Africa rift system

• Area where three continental plates are pulling apart

• Region yields lots of fossils

• Most of these fossil sites have been well dates

• Ash, chronometric dating techniques

• Lake habitat

Possible earliest evidence of bipedalism: Sahelanthropus tchadensis

• Chad

• 7-6 ma

• More vertical face, higher skull vault

• Smaller canines, no C-P3 honing complex

• Possibly biped, position of the foramen magnum

• Primitive in other respects (brain size, U-shaped dental arcade)

Possible earliest evidence of bipedalism: Orrorin tugenensis

• Kenya

• 6 ma

• Fragmentary cranial and postcranial remains

• Femoral morphology is indicative of bipedal locomotion

• Dental morphology is ape-like (large canines)

Ardipithecus

• Intermediate canine size between apes and later hominins

• 2009, “evolution’s bad girl”

  • Environment, reconstructed by its discoverers to be a more closed woodland habitat

  • 45% partial female skeleton

Ardipithecus kadabba

• 5.2 - 5.6 ma

• Projecting and interlocking upper and lower canines

• C-P3 complex was intermediate

Ardipithecus ramidus

• 4.4 ma

• Combination of primitive and derived traits

• Evidence of its ancestral position for the hominin clade for Ardipithecus discoverers

• Evidence of the position of A. ramidus as an early ape or an evolutionary side branch for others

• Relatively small brain, prognathism as in apes

• More forwardly-placed foramen magnum - consistent with bipedalism

• Reduced canine size

• Loss of C-P₃ honing

• Minimal sexual dimorphism

• Pelvis - possible evidence for bipedalism

  • Mosaic of characters for both bipedality and climbing

  • Short and broad ilium (unlike chimps)

  • Ischial surface is primitive

• Foot retains a divergent big toe

• Lacked other features for suspension/vertical climbing and knuckle walking seen in apes

Lovejoy’s model for the origins of bipedality

Major trends seen in australopiths (Australopithecus and Paranthropus)

• Dentition – reduced canine size; larger cheek teeth; thicker enamel

  • Paranthropus chewing adaptation, postcanine megadontia 

• Locomotion/posture – adaptations for bipedalism

• Relative brain size – not substantially enlarged compared to apes

• Body size - smaller than modern humans, with more sexual dimorphism

Geographical location of australopiths (Australopithecus and Paranthropus)

• Two kinds of bipedal ancestors with large teeth and small brains known from E. and S. Africa

• Australopithecus (gracile)

• Paranthropus (robust)

• Gracile forms now also found in Central Africa

The genus Australopithecus

• Australopithecus, meaning southern ape, was coined by a scientist in South Africa named Raymond Dart, after discovering the Taung child

• Not accepted for decades because of Piltdown

Piltdown hoax

• The Piltdown Man was a cranium and jaw, said to represent the fossilised remains of a previously unknown early human

• Fragments consisted of parts of a skull and jawbone, said to have been collected in 1912 from a gravel pit at Piltdown, East Sussex, England

• Eoanthropus dawsoni ("Dawson's dawn-man", after the collector Charles Dawson)

• Exposed as a fraud by geochemical tests showing the mandible and cranium couldn’t have come from the same sediments (1953)

  • Orangutan and modern human

Australopithecus anamensis

• 4.2 – 3.9 ma

• Kenya and Ethiopia

• Derived traits compared to apes:

  • Reduced canines 

  • Larger molars, thick enamel

  • Evidence of bipedalism

• Compared to later hominins, retains some primitive traits:

  • More U-shaped dental arcade

• Open woodland/gallery forest environment and open savanna environment

• Recently discovered MRD VP 1/1 cranium “puts a face to a name” for this species

  • Project Leader Yohannes Haile-Selassie

Australopithecus anamensis tibia

• 4.2 – 3.9 ma, Kenya

• Australopithecus anamensis

• Earliest undisputed evidence of bipedalism

• Enlarged proximal (top) end of the tibia

• Likely part of an ancestor-descendant lineage with A. afarensis

Australopithecus afarensis 

• Best-known early hominin species

• 3.9 - 2.9 ma

• East Africa

  • Kenya, Tanzania, and Ethiopia

• Finds:

  • Lucy

  • Dikika, Ethiopia

    • 3.3 ma

    • Apx. 3 years old

• Was smaller-bodied than modern humans

• Significant sexual dimorphism

  • A. afarensis: 56%

  • Gorilla: 50%

Lucy

• Australopithecus afarensis

• 3.2 mya

• 40% complete skeleton of a single individual

• 13 more individuals found in the same area as her

• Lumbar Curvature

• Valgus Knee

• Short toes

• More forward placement of the foramen magnum

• Short, broad pelvis; curved ilium

• Enlarged heel, arches, non-opposable big toe

Australopithecus afarensis: skull

• Sagittal crest

• Small brain size relative to face size

• Relatively prognathic

• Strong nuchal (neck muscles) crest for neck muscle attachments

Australopithecus afarensis: teeth and jaw

• Upper jaw

  • Canine further reduced

  • Posterior tooth rows near-parallel, converge slightly

• Lower jaw

  • Lower 3rd premolar usually bicuspid (not sectorial)

  • Slightly larger cheek teeth

• Thick molar enamel

  • Thick enamel on teeth suggest they may have eaten nuts, grains, or hard fruit pits, but also probably still eating fruits

Laetoli, Tanzania

• 3.6 ma

• Trail of fossil footprints in Laetoli, Tanzania

• Proves that a bipedal hominin lived in East Africa at the same time as A. afarensis

• 75 feet long trail made by three individuals who had crossed a thick bed of wet volcanic ash

• Adducted big toe

• Development of the arches

• Deep depression of the heel

  

Arboreal features of Australopithecus afarensis

• Relatively long and curved hand bones

• Highly mobile shoulder joints and upwardly-oriented shoulder blade

• Relatively long upper limbs compared to short lower limbs

Australopithecus afarensis: diverse habitats

• Lived in environments ranging from more closed woodland to dry open grasslands

• Ability to walk and climb trees would have allowed them to use resources from all of these environments

Early Australopithecus Fossil Sites

• Chad (Bahr el Ghazal)

  • Australopithecus bahrelghazali

  • 3.5 – 3.0 Ma

• Hadar and Middle Awash, Ethiopia

  • Australopithecus afarensis

• Kenya (Omo, W Turkana)

  • Australopithecus afarensis

• Tanzania (Laetoli)

  • Australopithecus afarensis

Kenyanthropus platyops

• East Africa

• 3.5 ma

• Distinctive combination of flat lower face and small molars

• Perhaps A. afarensis

Hominin localities – South Africa

• Plio-Pleistocene

• A. africanus

  • Makapansgat, Taung, Sterkfontein, Gladysvale

• Paranthropus

  • Sterkfontein, Kromdraai, Drimolen, Swartkrans

• Homo

  • Sterkfontein, Swartkrans

Australopithecus africanus: Taung child

• 3.5-2 ma

• South Africa

• Taung child, with endocranial cast

  • Grew up according to a schedule much like that of a chimpanzee

  • Thought have been attacked and killed by an eagle

Formation of South African sites

• Cave sites, formed as layers of bedrock were dissolved and filled with sediments

• No volcanic ash layers → chronometric dating is extremely difficult

  • Therefore using relative dating

“Osteodontokeratic culture”

• Bone tooth horn, “killer ape” theory

• Disproven by taphonomy

  • Dart

• Assemblages represent bone accumulations – hominins were not thought to have actually lived in these caves

Australopithecus africanus: Sts 5, female

• Slightly enlarged brain, & rounder cranial vault.

• Less prognathism compared to A. afarensis

• Less developed nuchal cresting

• Reduced anterior dentition

Australopithecus africanus: Cranial capacity

• Brain averaged 442 cc, which is slightly larger than A. afarensis

• Still, significantly smaller brains than modern humans (just ~ 1/3 the size)

Australopithecus africanus: Sts 71, male

• Cheek bones swept forward, nasal pillars 

• Robust mandible

• Larger cheek teeth with thick molar enamel

Australopithecus garhi 

• East Africa

• 2.5 ma

• Small brain (450cc), projecting face, with large front teeth like more gracile forms, and very large back teeth like more robust forms

• Limb proportions are unusual:  long forelimbs (as in earlier forms), but also with relatively long legs (as in Homo)

• Possible tool use

  • Found close to animals bones which show very clear signs of butchery with stone tools

Australopithecus sediba

• 2 ma

• South Africa

• Similarities with Australopiths:

  • Small brain size

  • Molar morphology

  • Small body size

  • Long upper limbs

• Similarities with Homo:

  • Projecting nose

  • Smaller teeth and chewing muscles

  • Longer legs

  • Hand with precision grip

• Berger and his colleagues have argued that A. sediba might be the long-sought species that gave rise to our genus (or a close relative of that species)

Major evolutionary trends at 2.5 M

• Significant cooling trend around 2.6 ma

• Expansion of open grasslands at the expense of closed forests

• Homo

  • Increase in brain size and capacity for tool making

  • Decrease in prognathism, and postcanine tooth size

  • Increase in body size

• Paranthropus

  • Hypermasticatory complex 

  • Increase in cheek tooth size

  • Body size similar to Australopithecus

Global cooling trend

Global cooling trend associated with drier, more open habitats in tropical Africa

Robust australopiths: Paranthropus

• Generate large bite forces at their molars, and made them extremely efficient at chewing

• Large and forwardly-placed sagittal crest

• Reorient chewing forces towards the back of the dentition

• Enlarged cheek teeth with thick molar enamel; frontal dental reduction and crowding

• Dished face

Paranthropus aethiopicus 

• East Africa

• 2.7-2.5 ma

• Classic robust features

• Well-developed sagittal and nuchal crests

• Prognathism; “dish-shaped” face

• Relatively small brain

• Well-developed sagittal crest

• Forward-projecting cheek bones (zygomatics)

Paranthropus boisei

• East Africa

• 2.3-1.2 ma

• Later robust australopith, “hyper-robust”

•  “Visor-like” (Darth Vader) face

• Forward-projecting cheek bones (zygomatics)

• Forwardly-placed sagittal crest

• Reduced prognathism

• Thick enamel

• Anterior dental crowding; marked reduction in incisors and canines

• Enlargement of premolars and canines; postcanine megadonty

P. boisei and P. robustus

• Paranthropus boisei

  • Olduvai Gorge, Tanzania in East Africa

  • 2.3-1.2 ma

• Paranthropus robustus

  • Several sites in South Africa, Kromdraai and Swartkrans

  • 2.0-1.5 ma

•  Both take this hypermastication trend to an extreme

•  Tough foods, especially during times of resource scarcity

  • Hard food objects, tough plants

  • Different types of foods, and that what they ate varied throughout the year – varied seasonally

The first “type fossils” of Homo habilis

• 1964, OH 24 (skull) and OH 7 (partial jaw)

• East and south Africa

• 2.4-1.4 ma

Why Homo habilis

• Found at Olduvai Gorge, Tanzania

• Found with flaked stone tools

• Slightly larger brain

• Oldowan tools

• Mary and Louis Leakey

Early homo

• Larger cranial capacity

• Slight reduction in size of the cheek teeth; more parabolic dental arcade; thinner enamel

• Reduced prognathism, more gracile cranium

• But, similar in body size to australopiths

  • Associated with stone tools

• Anatomically, they are more similar to Australopithecus

•  But classification as Homo has been classically supported by their ability to use and make stone tools (first tool-making species)

•  Now, evidence that other non-Homo species may have used tools

•  Is Australopithecus habilis a more accurate classification?

Early homo: one or two species

• H. rudolfensis

  • 2.4 – 1.6 ma

  • Larger brain size (mean = 775 cc)

  • Australopith-like broad midface

  • Relatively larger molar teeth

  • Well-developed mandible for chewing muscles

• H. habilis

  • 2.4 – 1.4 ma

  • Smaller brain size (mean = 612 cc)

  • Broader upper-face than midface

  • Smaller molars

  • Less robust mandible

  • More australopith-like limb proportions

Cranial capacity

      Range Average 

        (cm³)           (cm³)

Human       1150 - 1750   1325

Chimpanzee         285 - 500         395

A. afarensis         320-500       420

A. africanus         420-500       440

P. aethiopicus              410       410

P. robustus         475-530       512

H. habilis 612       612

H. rudolfensis KNM-ER 1470       775 

H. erectus (E. Africa)    900-1067         980

H. neanderthalensis   1125-1740          1415

Oldowan tool industry

• Early Stone Age / Lower Paleolithic; 2.6 Ma – 200 Ka

• Cores, flakes, and hammerstones

• Uses:

  • Access the carcasses of animals to obtain meat

  • Break bones to obtain marrow

• Secondary uses:

  • Plant processing

  • Woodworking

Cores

• Lumps of stone from which pieces are removed

• Can be used for a smaller variety of tasks, including chopping down a tree to make a digging stick or spear

Flakes

• Small fragments removed from cores

• Cutting through thick hide and butchering a large animal such as an elephant

Hammerstones

• Rounded stone used to remove the flakes

• Crack nuts, break open bones to get at the marrow inside

Swartkrans, South Africa tool use evidence

• 1.8-1.0 mya

• Digging tools made of bone and horn cores

  • Termites

• Evidence for selectivity

• Paranthropus or Homo?

Bouri, Ethiopia tool use evidence

• ~ 2.5 mya

• Percussion & cutmarks on bone

• No tools found

• Australopithecus garhi

Dikika, Ethiopia tool use evidence

• 3.39 mya

• Cutmarked bones

  • Flesh removal

  • Marrow access

• Not found in association with hominins or tools

• But, provides evidence for stone tool assisted meat consumption before Homo

Lomekwi

• 3.3 ma stone tools from  Lomekwi, Kenya

• Well before earliest Homo

Hominin tool traits shared with chimps

• Nut cracking

• Stone tool use

• Stone transport (<2km)

• Stone selectivity

• Small game hunting

Unique hominin tool traits

• Stone transport >10km

• Stone tool manufacture 

• Using tools to make tools (woodworking)

• Plant processing (USOs)

• Large game acquisition, carcass processing

• Earlier hominins may have used tools that do not have any trace in the fossil record → wood or other organic materials

Hunters or scavengers

• Hominins probably practiced both hunting and scavenging

• Opportunistic omnivores – incorporating a variety of plant foods, insects, and meat

Homo erectus sensu lato

• Homo erectus, H. ergaster

• 1.8 Ma - ca. 30 Ka (300/200,000)

• Cranial capacity ~ 880cm³

• First hominin to have a body stature and limb proportions more similar to modern humans

• First hominin species for which we have fossil evidence to migrate out of Africa into temperate regions of Asia and perhaps Europe

• Suggests that this species was committed to life on the ground

• May have been the first species to control fire

Pleistocene (1.8 Ma – 10 Ka) Climate Oscillation

• Colder and more variable climate starting at 1.8 mya

• Interval marked by repeated glacial cycles, known as the Ice Age

• Huge volumes of water in continental ice sheets

• Exposed land bridges connecting continents

Homo erectus/ergaster morphology

• Cranial

  • Long, low and flat

• Face

  • Broad flat face; less prognathic than H. habilis

  • Projecting nose

• Brain

  • Larger

  • Postorbital constriction

  • Avg cranial capacity = 1,000 cc (range over time from 750 – 1250 cc)

Homo erectus: one or two species

• Homo ergaster

  • Africa (~1.9 - 1.0 Ma)

• Homo erectus

  • Asia (1.8 Ma - ca. 30 Ka)

Geographical variation in Homo erectus

• Asian forms (Classic Zhoukoudien traits) - “Homo erectus”

  • Sangiran 17, Indonesia

    • Sagittal keel

    • Thick brow that forms a single torus, very pronounced

    • Receding forehead 

    • Sharp occipital angle (pronounced torus)

• African forms (with some exceptions) - “Homo ergaster”

  • KNMER 3733

    • No keel

    • Brows over each orbit, more curving

    • Less receding forehead

    • Less of an occipital angle

Footprints from 1.5 Ma, Ileret, Kenya (2009)

• Indistinguishable from the footprints made by modern humans, indicating a modern human-like form of bipedal locomotion

• Thought to have been made by Homo erectus

Turkana Boy

• KNM-WT 15000

• Homo ergaster

• Africa

• Adolescent skeleton, estimated at ~ 8 years of age based on dental development

• At an estimated stature of 5’3” (~ 6’ as an adult), indicates a significant increase in overall body size compared to Australopithecus

• Similar body proportions to modern humans

  
  

Acheulean tool industry

• 1.6 Ma – 200,000 years ago

• H. erectus

• More sophisticated technology  

•  Symmetrical, biface tools

•  Retouching, soft hammer percussion

Handaxe proportions follow a mental template (unlike oldowan tools)

• Tools have very regular proportions, standardized form

• Proportions hold for Africa, Near East, Europe

• Requires more complex cognitive abilities

Acheulean intelligence

• Requires more complex cognitive capabilities than the Oldowan

• Mental representation of a target image

• Advanced planning to arrive at that product, and ability to modify technique to achieve that goal

Handaxe usage

• “Swiss army knife”

• For processing large animal carcasses

  • Tip cuts through joints & meat

• Wood and other plants

• Cores (as flake dispensers)

• Not utilitarian purposes?

Control of fire: cooking

• Makes food more digestible

• Less food is needed to get the same amount of nutrients

• Some toxins can be neutralized

Control of fire: warmth

• Important in cold and seasonal environments out of Africa

• May have been crucial to allow migrations to Asia and Europe

Control of fire: cave occupation

• Allows the use of caves as shelters

• Also important in the colonization of European and Asian environments

Control of fire: predator protection

• Especially important for large groups

• Might be predated upon at night