HUMAN EVOLUTION

A.Hominids- Evolved during the Miocene Epoch

1. Proconsul- among the oldest known hominoids- had features that suggest a close link to the

common ancestors of apes & humans

*Proconsul heseloni – species that lived in the trees ofdense forests in eastern Africa (20million years ago)

- an agile climber; w/ flexible backbone & wide rangeof movement

2. Afropithecus - evolved about 18 million years ago in

Arabia & Africa after the large apes underwent several radiations

3. Kenyapithecus – from Africa4. Griphopithecus – from western Asia5. Dryopithecus – from europe

* Appropriate classification of Hominoids = ?

Humans as Apes

•About 98% of the genes in people & chimpanzee – are identical

Modern humans – have a number of physical characteristics reflective of an ape ancestry

a. Shoulders with a wide range of movement b. Fingers capable of strong grasping

Both – have larger brains & greater cognitive ability than do most other mammals

Differences of modern humans from apes:

1.Much larger and more complex brains2.Unique intellectual capacity3.Elaborate forms of culture and

communication4.Habitually walk upright5.Can manipulate very small objects6.With a throat structure that makes speech

possible

The first Humans: Australopithecines

-First evolved around 5 million years ago in Africa; an ape-like species

2 important traits that distinguished it from apes:a. Small canine teethb. Bipedalism

• Ardipithecus – the earliest Australopith species known today

* Australopithecus and Paranthropus – other species

Transition from Ape to Human:

Adaptations that marked the transition fromape to human:

-Australopiths – resembled the apes in terms of the face and amount of hair in the body; brain size (therefore probably with ape-like mental abilities; social

life similar to chimpanzees

Australopith Characteristics:

•Bipedal stance; habitual upright walking

1.Low cranium behind a projecting face2.Brain size of 390 to 550 cubic cm (in the range

of an ape’s brain)3.Body weight range: 27 to 49 kg4.1.1 to 1.5 m tall5.Large degree of sexual dimorphism, males much

larger than females6.Had curved fingers & long thumbs with a wide

range of movement

4 species of early australopiths:

- One from Genus Ardipithecus; 3 from Genus Australopithecus

(1)Ardipithecus ramidus-fossils – had a very ancient combination of

apelike and humanlike traits-teeth – had a thin outer layer of enamel-skeleton shows strong similarities to chimpanzee but with slightly reduced canine teeth-adaptations for bipedalism

(2) Australopithecus anamensis

1965 – discovery by a research team of Harvard Univ. of a single arm bone of an early humanat Kanapol, Northern Kenya

1994- discovery by Meave Leakey of numerous teeth & bone fragments at same site

- fossils discovered – about 4.2-3.9 million years old - skull appeared ape-like; enlarged tibia – indicated

bipedal walking (supports full body weight)

(3)Australopithecus afarensis- a gracile australopith that thrived in eastern Africa (about 3.9-3 million years ago)

*Lucy – the most celebrated fossil of this species- discovered by Donald Johanson in 1974 at hadar, Ethiopia

- also discovered in Laetoli, northern Tanzania (1978)by Mary Leakey; best known for its spectacular trails of bipedal human footprints

-Foot anatomy & gait did not exactly match those of modern humans – indication that they not only lived on the ground but also on trees

-Skeleton of Lucy – indicates that it had longer, more powerful arms than most later human species (adept to climbing trees)

-Height of Lucy – only 1.1m (3.5 ft) tall; other similar fossils – about 1.5 m tall

Possibilities:- 2 species; one highly dimorphic species; large adults (males), small adults (females)

(4)Australopithecus africanus

- thrived in the Transvaal region (now South Africa) between about 3.5 – 2.5 million years ago

- discovered by Raymond Dart (1924) in Taung, South Africa

- specimen as of a young child – Taung Child

- late 1930s – Robert Broom – unearthed many more of these skulls from the Transvaal site

Globular braincase and less primitive-looking face and teeth than A. afarensis - features of A. africanus which scientists considered to be a likely ancestor of the genus, Homo

Heavily built facial and cranial features – were thought to be signs of being ancestors of the robust australopiths that lived later in same region

1998 – Ronald Clarke – unearthed an almost completeearly australopith skeleton in Sterkfontein

Late Australopith

-Evolved around 2.7 million years ago-Had megadont cheek teeth – wide molars and premolars coated with thick enamel-With small incisors-Robusts had expanded, flattened and more vertical face than the gracile australopiths-had a sagittal crest on top of head to which thick jaw muscles were attached-zygomatic arches curved out wide from side of face and cranium –for massive chewing muscles to pass through

•Research revelations: - Robust australopiths actually stood about same height and weight as A. afarensis & A. africanus

(1)A. aethiopicus - the earliest known robust species

- lived in eastern Aftica about 2.7 million years ago

*”Black skull” – a 2.5 million year old skull fossil discovered in 1985 at West Turkana, Kenya by Alan Walker

- helped define this species - with similar primitive features as A. afarensis

(2)A. boisei- the other ell-known East African robust australopith- lived between about 2.3 and 1.2 million years ago

1959 – Mary Leakey – discovered the original fossil of this species – a nearly complete skull at the site of Olduvai Gorge, Tanzania

Louis Leakey – originally named the new species as Zinjanthropus boisei (East African Man)

Features:

1.Skull – dates back from 1.8 million years ago2.Has a massive, wide and dished-in face capable

of withstanding extreme chewing forces3.Molars four times the size of those in modern humans

(3)A. robustus- southern robust species which lived between about 1.8 and 1.3 million years ago in Transvaal

1938 – Robert Broom – found a fossil jaw and molar that looked different from those of A. africanus

- named a new species, Paranthropus robustus

-Late 1940s & 1950 – discovery by Broom of many more fossils of this species at the Transvaal site of Swartkrans

Fate of the Late Australopith:- Last robust australopiths – died out about 1.2 million years ago

*Factors which may have contributed to their decline:a. Fluctuation in climate patterns around the world - reduced the food supply on which robusts depended

b. Interaction with larger-brained members of thegenus, Homo

c. Competition with several other species of plant-eating monkeys and pigs

The Genus Homo

-Have evolved at least 2.3 million to 2.5 millionyears ago

*Larger brains – made them distinctly differentfrom their predecessors

Three periods in the evolution of Homo:a.Early Homo – resembled gracile australopiths;

- lived until possible 1.6 & 1.8 million years agob.Middle Homo – began perhaps between 2 million

and 1.8 million years ago- Species evolved an anatomy similar to modern humans but with smaller brains

c. Late Homo – around 200,000 years ago - species have evolved large and complex brains

and eventually language - evolution of culture

A. Early Homo

2 species:a. Homo habilis*early 1960s – Louis Leakey, John Napier &

Philip Tobias- discovered in Olduvai Gorge, Tanzania , a group of early human fossils that showed a cranial capacity above the range of that in known australopiths

Features:

1.Evolved between 1.6 million and 2.4 million yrs ago2.Lived in eastern and possibly South Africa3.Has a cranial capacity from 590 to 690 cu cm.4.With smaller and narrower molar teeth, premolar

teeth and jaws5.Exhibited sexual dimorphism6.Ratio of length of arms to legs greater than that in

the australopith Lucy7.With very ape-like body proportions8.Had more modern-looking feet and hands capable of

producing tools

b.Homo rudolfensis

Features:1.Named after Lake Rudolf2.Date from about 1.9 million years ago3.Had a larger face and body than did H. habilis4.Cranial capacity – about 750 cu cm5.Had fairly large teeth6.Thigh bones found by scientists – suggest a body

size of 1.5 m (5 ft) and 52 kg (114 lbs)

Middle Homo

1.Homo ergaster- evolved in Africa around 2 million years ago- had a rounded cranium with a brain size of\ 800 to 850 cu cm- with a prominent brow ridge- small teeth, and many features it shared with the

later H. erectus

*Turkana Boy: the most important fossil of this species- had elongated leg bones and arm- leg and trunk proportions – match those of modern

humans- quite tall and slender

Indications in terms of the anatomy of the Turkan Boy:a.Well adapted in terms of walking and for running

long distances in a hot environmentb.No significant amount of tree climbing

(2)Homo erectus

- Humans – first evolved in Africa- Southeast Asia - w here the earliest human species

known to have spread in large numbers were firstdiscovered.

*Eugene Dubois – found the cranium of an early human on the Indonesian Island of Java (called Pithecanthropus erectus) - “erect ape-man, but today called Homo erectus

Features:

1.Appears to have evolved in Africa between1.8 million and 1.5 million years ago

2.With a low and rounded braincase that was elongatedfrom front to back

3.Prominent brow ridge4.With an adult cranial capacity of 800 to 1,250 cu cm

(twice that of australopiths)5, Thicker bones than those of earlier species6.Prominent muscle markings and thick, reinforced

areas on the bones – indicative of a body that couldwithstand powerful movements & stresses

7. With much smaller teeth than australopiths8. With heavy and strong jaw

1920s and 1930s – Franz Weidenreich - excavated the most famous collections of H. erectus fossils from a cave at the site of Zhoukoudian, China

- called these Sinanthropus pekinensis or Peking Man; later reclassified as H. erectus

(3)Homo heidelbergensis

- many paleoanthropologists – believed that early humans migrated into Europe by 800,000 years ago

and that these were not H. erectus

- considered to be early migrants into Europe who predated both Neanderthals and H. sapiens in the region

- name comes from a 500,000 year old jaw found near Heidelberg, Germany

-Considered to be massive-boned and larger-brained humans replacing populations of H. ergaster

-Fossils of these found at sites in Bodo, Ethiopia; Saldanha, South Africa; Ndutu, Tanzania and Kabwe, Zimbabwe

-Were thought to have given rise to both Neanderthals (in Europe) and H. sapiens (in Africa)

Late Homo

Neandertals and other Archaic Humans

-Lived in areas ranging from Western Europe through Central Asia from about 200,000 to between 36,000 and 24,000 years ago

-Name comes from fossils found in 1856 in the Feldhofer Cave in the Neander Valley in Germany

•Engis, Belgium (1829) & Forbes Quarry, Gibraltar (1848) – where there were prior discoveries also representing Neandertals

Features:1.Walked fully upright without a slouch or

bent knees2.Cranial capacity quite large (about 1500 cu cm),

slightly larger than that of modern humans

Differences from Modern Humans:3.Skull with a low forehead4.Large nasal area (suggesting a large nose)5.Forward-projecting nasal and cheek region6.Prominent brow ridge with a bony arch over

each eye5.A non-projecting chin6.An obvious space behind the third molar

7. With a more heavily built and large-boned skeleton8. Bowing of the limb bones in some9. Broad scapulae (shoulder blades)10 .hip joints turned outward11. With a long and thin pubic bone12. With a short lower leg and arm bones relative to the upper bones13. With large surfaces on the joints of the toes and limb bones

•These traits made a powerful, compact body of short stature (males = 1.7 m & 84 kg; females = 1.5 m and 80 kg.)

Archaic Species – fossils, which, according to scientists, are distinct from but similar to those of Neanderthals

Modern Homo sapiens:

1.Oldest known fossils that possess skeletal physical features typical of modern humans – date from

between 130,000 and 90,000 years ago2.Have smaller bro ridge, if any3.Globe-shaped braincase4.Flat or only slightly projecting face of reduced size,

located under the front of the braincase

* Only humans among all mammals have a face positioned directly beneath the frontal lobe of the brain

5.Cranial capacity ranges from about 1,000 to 2,000 cu cm, with the average being about

1,350 cu cm.