8 C H A P T E R EARLY HOMININS 8-2

EARLY HOMININS What Makes Us Human? Chronology of Hominin Evolution Who Were the Earliest Hominins? The Varied Australopithecines The Australopithecines and Early Homo Oldowan Tools 3

EARLY HOMININS What key traits make us human, and when and how are they revealed in the fossil record? Who were the australopithecines, and what role did they play in human evolution? When and where did hominins first make tools?

WHAT MAKES US HUMAN? What determines whether a fossil is a human ancestor? Look for similarities in DNA Such key attributes as bipedal locomotion, a long period of childhood dependency, big brains, and use of tools and language Some physical markers identify certain fossils as early hominins but were lost during subsequent human evolution

BIPEDALISM Ardipithecus (5.8–4.4 m.y.a.): earliest recognized hominin genus; shows capacity for upright bipedal locomotion Reliance on bipedalism (upright two-legged locomotion) differentiates the early hominins from apes Traditionally viewed as adaptation to open grassland, however, Ardipithecus lived in humid woodland habitat Perhaps bipedalism developed in woodlands but became more adaptive in subsequent savanna habitat Ability to see over long grass, carry items back to a home base, and reduce body’s exposure to solar radiation Preceded stone tool manufacture and the expansion of the hominin brain Bipedal but also preserved enough apelike anatomy to make them good climbers

Ardipithecus

Bipedalism Traditional Theories Stressed advantages in a habitat increasingly dominated by dry, savanna-like conditions However, ardipithecus lived in woodland environment Bipedalism my have developed in the woodlands and became even more advantageous in the savanna habitat

Woodlands and Savannah

Advantages Ability to see further See predators See food Arms free to carry items Tools and weapons More energy efficient Requires less fuel Less body surface area exposed to solar radiation Facilitates cooling Reduces fluid loss Can look for food in sunlight conditions

BRAINS, SKULLS, AND CHILDHOOD DEPENDENCY Early hominins had very small brains compared to modern humans (little bigger than average chimp) Brain size increased during hominin evolution, especially with genus Homo Human children have long period of childhood dependency, during which brains and skulls grow dramatically (compared to the young of other primates) Larger skulls mean larger birth canals, but bipedalism imposes limits on the expansion of human pelvic opening Pelvis too big – doesn’t provide enough support for the trunk causing problems with locomotion and posture Pelvis too small – mother and child may die Natural selection struck balance between structural demands of upright posture and tendency toward increased brain size – the birth of immature and dependent children whose brains and skulls grow dramatically after birth

TOOLS Hominin stone tool manufacture dated to 2.6 m.y.a. Upright bipedalism permitted use of tools and weapons Primates have abilities to adapt through learning; Most likely, early hominins had even greater cultural abilities than contemporary apes have

TEETH Big back teeth with thick tooth enamel: an early hominin trait (that has been reduced during subsequent human evolution) Permitted thorough chewing of tough, fibrous vegetation that would have otherwise been indigestible Churning, rotary motion associated with such chewing favored reduction of canines and bicuspids These front teeth are much sharper and longer in the apes than in early hominins

Teeth

CHRONOLOGY OF HOMININ EVOLUTION Hominid: the zoological family that includes fossils and living humans, chimpanzees, gorillas, and their common ancestors Hominin (tribe) describes all human species that have ever existed, excluding chimps and gorillas

CHRONOLOGY OF HOMININ EVOLUTION Hominins appeared late in the Miocene epoch (23 – 5 mya) The most important epochs for study of hominin evolution are the Pliocene (5–2 m.y.a.) - Austalopithecus Pleistocene (2 m.y.a.–10,000 B.P.) – Au. Had evolved into homo Holocene or Recent (10,000 B.P.–present) Australopithecus main hominin genus until end of Pliocene Some form of Australopithecus evolved into Homo by start of Pleistocene

WHO WERE THE EARLIEST HOMININS? Significant recent discoveries in Africa Kenya Tanzania Ethiopia South Africa Chad

Table 8.1: Dates and Geographic Distribution of Major Hominoid, Hominid, and Hominin Fossil Groups 18

SAHELANTHROPUS TCHADENSIS 6- to 7-million-year-old skull, two lower jaw fragments, and three teeth; OLDEST POSSIBLE HUMAN ANCESTOR yet found Also known as “Toumai” (“hope of life”) Central Africa – Chad (2001) Time period when humans and chimps were diverging from common ancestors Blends ape-like and human characteristics: Heavy brow ridges Adult male with chimp-sized brain Relatively flat, humanlike face Teeth Foramen magnum – “big hole” through which spinal cord joins the brain; placement is farther forward than in apes; suggests bipedal locomotion Moves scientists closer to time when humans and African apes diverged If hominin, shows hominin evolution not confined to E. Africa’s Rift Valley

ORRORIN TUGENENSIS Kenya - 2001 6-million-year-old fossils from at least five individuals suggest upright bipedalism and tree-climbing skills Close to time of common ancestor between humans and chimps Chimp-sized creature that climbed easily and walked on two legs when on the ground Teeth more like a female chimpanzee Other dental and skeletal features, especially bipedalism, led discoverers to assign Orrorin to hominin lineage – it is debated issue Lived after Toumai but before Ardipithecus kadabba Hominin status of Ardipithecus more generally accepted

ARDIPITHECUS Dates to at least 4.4 m.y.a. Subsequently, FOSSILS from 5.8 m.y.a. found in Ethiopia (Ardipithecus kadabba) (1992 – 1994) At least five individuals represented Apelike in size, anatomy, and habitat (mixture of woods and grasslands) Because of its probably upright bipedalism, Ardipithecus kadabba has been recognized as the earliest hominin Ardipithecus ramidus (4.4 m.y.a.) is earliest known hominin SKELETON 21

ARDIPITHECUS Ardipithecus ramidus - “Ardi”; female - Ethiopia – 2009 Fairly complete skeleton; earliest known hominin skeleton; almost 1.2 million years older than Lucy; fossils date from 5.8 to 4.4 mya Skeleton: Seems to be transitional between earlier arboreal primates and later terrestrial ones Pelvis – transitional; suited for arboreal climbing and bipedal locomotion Brain no larger than that of modern chimp Retained arboreal heritage in lower pelvis Strong hamstrings for climbing Lack of arched feet Long arms and short legs Wooded environment Teeth suggest omnivorous diet less dependent on fruits (ate plants, nuts, and small mammals); no heavy chewing specializations of later australopithecus species Reduced sexual dimorphism – canines resemble modern humans rather than chimps or gorillas (smaller and less tusk-like)

KENYANTHROPUS Maeve Leakey’s Kenyanthropus platyops complicates picture Kenya – 1999 Flat faced “man” of Kenya Nearly complete skull and partial jawbone 3.5 million year old find represents a new branch on early human family tree Shows at least two hominin lineages existed as far back as 3.5 m.y.a. (au. afarensis, “Lucy”, and Kenyanthropus); THEY WERE NOT ALONE Kenyanthropus has flattened face and small molars, suggesting to Leakey a new taxon (very different from au. afarensis)

Figure 8.1: Phylogenetic Tree for African Apes, Hominids, and Hominins 24

THE VARIED AUSTRALOPITHECINES Australopithecus had at least 7 species A. anamensis (4.2–3.9 m.y.a.) A. afarensis (3.8–3.0 m.y.a.) A. africanus (3.0?–2.0? m.y.a.) A. garhi (2.5 m.y.a.) A. robustus (2.0?–1.0? m.y.a.) A. boisei (2.6?–1.2 m.y.a.) A. sediba (1.98–1.78 m.y.a.)

Austalopithecus

Australopithecus

AUSTRALOPITHECUS ANAMENSIS Ardipithecus ramidus may or may not have evolved into Au. anamensis Fossils (78 fragments) from two sites, reported first by Leakey and Walker, date to 4.2–3.9 m.y.a. Strong jaws Molars have thick enamel Large apelike canines Suggests, at times, ate hard, abrasive food (probably preferred fruits and nuts) Weighed about 110 pounds Bipedal May be ancestral to A. afarensis, which is usually considered ancestral to all later australopithecines as well as Homo species

Austalopithecus Anemensis

AUSTRALOPITHECUS AFARENSIS A. afarensis lived 3.8–3.0 m.y.a. Fossils found at two sites (Laetoli in northern Tanzania and Hadar in Ethiopia) Very similar to chimps and gorillas; indicates common ancestry with African apes must be recent (no more than 8 m.y.a.) “Lucy” – from Hadar; approximately 3.2 million years old

Lucy

Lucy’s Baby “Lucy’s Baby” - female Ethiopia; 2000 Lived 100,000 years before Lucy; 3.3 million years ago Remains include: almost complete skull, baby teeth, fingers, torso, kneecap, foot Monkey size face with smooth brow Skull and upper body appear ape-like Lower body confirms bipedalism Upper body includes two complete shoulder blades similar to a gorilla’s (better at climbing than humans) World’s oldest fossil child – sheds light on growth cycle of Australopithecus brain: Growth cycle similar to chimps; allows less time for guidance and socialization Chimps reach puberty around age 7 and males leave their mother around age 10 Reached adulthood earlier than modern humans Developed rapidly - lifespan would have been shorter than ours

Lucy’s Baby

Australopithecus Afarensis

AUSTRALOPITHECUS AFARENSIS CHARACTERISTICS: Skull and upper body are ape-like; Llwer body confirms bipedalism Teeth and Face - Canines, premolars and skulls were more ape-like Longer and sharper canine teeth (compared to Homo) that projected beyond other teeth; canines were smaller than ape’s tusk-like canines Lower premolar – pointed and projecting to sharpen upper canine teeth; had one long cusp and one tiny bump that hints at bicuspid premolar that eventually developed in hominins Molars, chewing apparatus, and cheekbones foreshadowed later hominin trends Massive back teeth, jaws and facial and cranial structures suggest diet demanding extensive grinding and powerful crushing (hard, gritty, fibrous vegetation of grasslands and semi-desert) (back teeth change to accommodate heavy chewing stresses) Cheekbones large and blare out to the side for attachment of powerful chewing muscles

AUSTRALOPITHECUS AFARENSIS Bipedalism – predates Au. Afarensis Structure of pelvic, hip, leg, and foot bones confirm bipedalism Pelvis is more similar to Homo than to ape’s (but not identical) Blades of Australopithecine pelvis are shorter and broader than those of apes Sacrum is larger, as is Homo Lower spine (lumbar) curve characteristics of Homo; curvature helps transmit weight of upper body to pelvis and legs Skull - Brain capacity only slightly larger than modern chimp

Au. Afarensis Foramen Magnum “Big hole” through which spinal cord joins the brain Placement is farther forward in Australopithecus and Homo Represents adaptation to upright bipedalism Arms Muscular Longer arms relative to legs Likely spent some time in trees ADAPTATIONS TO LIVING BOTH IN TREES AND ON THE GROUND HELPED AUSTRALOPITHECUS AFARENSIS SURVIVE FOR ALMOST A MILLION YEARS.

AUSTRALOPITHECUS AFARENSIS Birth Canal - Most significant contrast Narrower in Australopithecus than in Homo Expansion of birth canal is trend in hominin evolution Width of birth canal is related to size of brain and skull Australopithecine skull grew after birth to accommodate a growing brain (like Homo) but it expanded less than ours do Sexual Dimorphism Very marked; males weighed perhaps twice as much as females (Lucy stood between 4-5 feet tall; male Australopithecus might have reached 5 feet)

Au. Afarensis Childhood Young would have depended on parents and kin for nurturance and protection Years of childhood dependency would have facilitated social learning by providing time for observation, teaching, and learning Suggests possibility of rudimentary cultural life Au. anamensis and Ardipithecus indicate bipedalism; thus, bipedalism predates Au. afarensis as well as larger brain size

RECAP 8.1: Facts about the Australopithecines Compared with Chimps and Homo 40

Figure 8.3: Comparison of Homo sapiens and Pan troglodytes (the Common Chimp) 41

Figure 8.4: A Comparison of Human and Chimpanzee Pelvises 42

Figure 8.5: A Comparison of the Skull and Dentition (Upper Jaw) of Homo and the Chimpanzee 43

GRACILE AND ROBUST AUSTRALOPITHECINES Two groups of South African australopithecines (3–1 m.y.a.) Gracile (A. africanus): smaller and lighter; Robust (A. robustus): larger than gracile, robust A. boisei - hyperrobust 3 Conflicting models: 1.) Africanus and robustus as separate species; life spans were overlapping 2.) africanus and robustus as sequential; africanus was ancestral to robustus 3.) both groups were part of single species; each represents opposite extremes of variation within one species Both gracile and robustus probably descended from A. afarensis

GRACILE AND ROBUST AUSTRALOPITHECINES Trend toward enlarged back teeth, chewing muscles, and facial buttressing continues However, canines are reduced and premolars are fully bicuspid Front teeth are more marked than Homo Chewing muscles are strong enough to produce sagittal crest (bony ridge on top of skull Cheekbones were elongated, massive structures that anchored large chewing muscles running up the jaw Brain size increased slightly from A. afarensis (430 cm3) to A. Africanus (490 cm3) to A. robustus (540 cm3); compare to Homo sapiens (1,350 cm3) The skulls, jaws, and teeth of australopithecines indicate their diet was mainly vegetarian, requiring extensive crushing and grinding; they may also have hunted small and slow moving game or scavenged Living in open savanna, they probably sought safety and companionship in groups; maintained social bonds though play and mutual grooming Sexual dimorphism is evident; observed through size of canine teeth Sexual dimorphism was much more pronounced in early hominins than in Homo Sapiens Later australopithecines had bigger back teeth than earlier ones; trend of enlarged back teeth ended with early Homo (who had much smaller back teeth, reflecting dietary change)

GRACILE AND ROBUST AUSTRALOPITHECINES The 1985 discovery of “black skull” (2.6 m.y.a.) apparently an early A. robustus Walker and Leakey view skull as an early hyperrobust A. boisei Gives more possible models of divergence between Homo and Australopithecines Has mixture of Au. features Ape like jaw and relatively small brain Sagittal crest (like hyper-robusts) Shows that some anatomical features did not change much during more than 1 million years

Figure 8.6: Skulls of Robust (left) and Gracile (Right) Australopithecines, Showing Chewing Muscles 47

THE AUSTRALOPITHECINES AND EARLY HOMO Homo ancestors became reproductively isolated from later australopithecines by 2 m.y.a. Hominin teeth fossils from 2 m.y.a. are two very different sizes Very large teeth belonged to Au. boisei Smaller teeth belonged to members of genus Homo By 1.9 m.y.a., fossil evidence shows different hominin groups occupied different ecological niches (Homo and Au. boisei coexisted in East Africa) (early Homo habilis and Homo erectus) Johanson and White (1979) propose that Au. afarensis split into two populations: other australopithecines and early homo Homo had a larger brain and reproportioned skull (increase in areas of brain that regulate higher mental function), hunted and gathered, made sophisticated tools, and eventually displaced its cousin species, A. boisei

Homo Trends The distinctive early Homo trends are 1. A rapid increase in brain size and reproportioned skull (increased areas of function), 2. Increasingly elaborate toolmaking 3. Increasing emphasis on hunting and gathering There remains considerable debate as to when and in what population these trends led to speciation, from an australopithecine to Homo habilis. Homo erectus likely displaced cousin Au. Boisei

OLDOWAN TOOLS Oldest manufactured tools; found by Leakeys First tools found were from Olduvai Gorge (found in 1931) are about 1.8 m.y.a. Older Oldowan tools found in Ethiopia, Congo, Kenya, and Malawi (2.6-2 million years old) Stone tools consist of cores and flakes and choppers Core: piece of rock from which flakes are removed Flake: piece that is knapped or chipped off of a core Chopper: tool made by flaking the edge of such a core on one side (byproduct of flaking the core) (not a preconceived form)

Oldowan Tools Core tools and choppers are not the most common stone tools; FLAKES are! Choppers used for: Food processing (pounding, breaking, bashing) Dismember game carcasses Break open marrow cavities Oldowan sites have also produced pieces of bone and horn with scratches indicating they were used for digging up tubers or insects

OLDOWAN TOOLS Oldowan pebble tools represent world’s oldest formally recognized stone tools For decades, anthropologists have debated the identity of early toolmakers. It has been widely accepted that homo habilis was the first hominin toolmaker; however it is likely that at least one kind of australopithecine also made and used stone tools

A. GARHI AND EARLY STONE TOOLS In 1999, new hominin species, A. garhi (means “surprise”), was found in Ethiopia; dates to 2.6-2.5 m.y.a. Associated with stone tools, remains of butchered animals (antelopes and horses butchered with earliest stone tools) Important discovery for three reasons: Added new species to human family tree Demonstrated thigh bone elongated 1 million years before forearm shortened, to create current human proportions Evidence of butchering of large mammals shows early stone technologies were aimed at getting meat and marrow from big game; may be the beginning of dietary revolution that eventually led to occupation of new habitats and continents The association of Au. garhi with animal butchery combined with the earliest stone tools suggests that australopithecines were tool-makers with some capacity for culture

Oldowan Hominins at the Kanjera Site Provides the earliest, and very complete, evidence for “persistent” reliance on meat within the hominin diet (don’t know which species of hominin though) A regular diet of red meat was a key factor that allowed the growth of the hominin body and brain and the spread of hominins beyond Africa