Hominid Evolution

Chapter 19

Classification Hierarchy (Linnaeus)

Kingdom AnimalPhylum Chordate

Class MammalOrder Primates

Family HominidsGenus Homo

Species Sapiens

Humans and apes diverged ~8 Mya

Humans and Apes

• Diverged ~8 million years ago

• >12 different forms of hominids since then

• Sahelanthropus tchadensis, – the oldest

known hominid – 7 million years

old– discovered in

2002 in Chad

Oldest Hominid

• Skull found in the African nation of Chad in 2002– pushed back the origins of humans to nearly 7

million years ago– its discovery has raised more questions than it

answered

Sahelanthropus tchadensis

• Paleoanthropologists now think – human evolution branched many times – rather than evolving in a somewhat straight line

• Key traits such as • upright walking• manual dexterity • “large” brain

– evolved more than once, and produced many evolutionary dead-ends

“Bushy” Model of Human Evolution

Fossil hominids

http://www.nature.com/nature/journal/v418/n6894/fig_tab/418133a_F2.html

• Sahelanthropus tchadensis shows a mosaic of primitive and advanced features

• The small brain case and most of the teeth are chimplike

• Fairly flat nose and the prominent brow ridges – are features only seen, until now, in the human genus Homo

• Looks more human than hominids that came millions of years later!

Oldest Hominid

• Much of our knowledge– comes from fossils found in a small desert area

southwest of Cairo, Egypt

• During the Late Eocene and Oligocene– this region was a lush, tropical rain forest – supported a diverse and abundant fauna and flora

Early History of Ancestral Hominids

• Several thousand fossil specimens

– representing more than 20 species of primates

– recovered from rocks of this region

• One of the earliest ancestral hominids

– was Aegyptopithecus,

• small, fruit-eating, arboreal primate

• weighed about 5 kg

Thousands of Fossil Specimens

One of the Earliest Ancestral Hominids

• Skull of Aegyptopithecus zeuxis,

– one of the earliest known anthropoids

– ~30 Ma

• The hominids (family Hominidae)– primate family that includes present-day humans – fossil record extending back 7 million years

• Hominids are bipedal– that is, they have an upright posture– Skeletal structure shows bipedal traits

• Hominid brain organization: larger compared to other primates

Hominids

• Comparison between quadrupedal and bipedal locomotion– in gorillas and humans

Comparison of Locomotion

• In gorillas the ischium bone is long – and the entire pelvis is

tilted toward the horizontal

• In humans the ischium bone is much shorter

• and the pelvis is vertical

Comparison of Locomotion

• Comparison between quadrupedal and bipedal locomotion– in gorillas and humans

• In addition, hominids show a trend – toward a large and internally reorganized brain

• A large brain size and organization – is apparent in the brain of a present-day human

Hominids: Larger Reorganized Brain

• Many anthropologists think – hominid features evolved in response to major

climatic changes

• During this time– vast savannas replaced the African tropical rain

forests – where the lower primates had been so abundant

Response to Climatic Changes

• As the savannas and grasslands continued to expand– hominids made the transition from true forest

dwelling – to life in an environment of mixed forests and

grasslands

Mixed Forests and Grasslands

Geologic Age Ranges

• Discovered in Chad in 2002– nearly 7-million-year-old skull and dental remains

of Sahelanthropus tchadensis – make it the oldest known hominid yet unearthed

Oldest Known Hominid

• Australopithecines are early hominids– genus Australopithecus

• Currently, five species are recognized: – A. anamensis– A. afarensis– A. africanus – A. robustus– A. boisei

Australopithecus

• Many paleontologists accept that – A. anamensis

• the oldest known australopithecine,

– is ancestral to A. afarensis, • who in turn is ancestral to A. africanus

• and the genus Homo,

• as well as the side branch of australopithecines – represented by A. robustus and A. boisei

Evolutionary Scheme

• A reconstruction of Lucy’s skeleton

• Lucy is a ~ 3.5-million-year-old – Australopithecus afarensis

Lucy

• Knees worked like modern human knees

• Makes 40% bigger than females

• Males had large crests on the tops of their skulls

• Preserved in volcanic ash in Tanzania– Discovered in 1978

– Proved hominids were bipedal walkers at least 3.5 million years ago

Hominid Footprints

Hominid Footprints

• Most scientists think the footprints – were made by

Australopithecus afarensis

– whose fossils are found nearby

• A. afarensis had a brain size of 380–450 cubic centimeters (cc), – larger than the 300–400 cc of a chimpanzee – much smaller than that of present-day humans

(1350 cc average)

Brain Size of A. afarensis

• The skull of A. afarensis retained many apelike features– massive brow ridges – forward-jutting jaw– teeth were intermediate between those of apes and

humans

• The heavily enameled molars – adaptation to chewing fruits, seeds, and roots

Apelike Features

Landscape with A. afarensis

• Re-creation of a Pliocene landscape – showing

members of

– Australo-pithecus afarensis

– gathering and eating

– various fruits and seeds

• A reconstruction of the skull – of Australopithecus

africanus

• This skull, – known as that of the

Taung Child, • was discovered by

Raymond Dart in South Africa in 1924

– and marks the beginning of modern paleoanthropology

Skull of A. africanus

• It appears the limbs – of A. africanus may not have been as well adapted

for bipedalism as those of A. afarensis

Not As Well Adapted for Bipedalism

Homo habilis • The earliest member of our own

genus Homo– lived 2.5-1.6 million years ago

• H. habilis evolved from the A. afarensis and A. africanus lineage – coexisted with A. africanus for about

200,000 years

The Human Lineage: handy man

• The geologic age ranges – for the commonly accepted species of hominids

Geologic Age Ranges

• H. habilis had a larger brain (700 cc average) – than its australopithecine ancestors but smaller

teeth

• It was about 1.2-1.3 m tall and weighed 32-37 kg

Characteristics of Homo habilis

• In contrast to the australopithecines and H. habilis, – which are unknown outside Africa, – Homo erectus was a widely distributed species– migrated from Africa during the Pleistocene

• Specimens have been found – not only in Africa – also in Europe, India, China ("Peking Man"), and

Indonesia ("Java Man")

Homo Erectus

• H. erectus evolved in Africa 1.8 million years ago – and by 1 million years ago – was present in southeastern and eastern Asia, – where it survived until about 100,000 years ago

Survived in Asia Until About 100,000 Years Ago

• Although H. erectus developed regional variations in form, – the species differed from modern humans in several

ways

• Its brain size of 800-1300 cc, – though much larger than that of H. habilis, – was still less than the average for Homo sapiens

(1350 cc)

H. erectus Differed From Modern Humans

• H. erectus's skull was thick-walled– face was massive– prominent brow ridges – teeth were slightly larger than those of present-day

humans

• H. erectus was comparable to size to modern humans– between 1.6 and 1.8 m tall – weighing between 53 and 63 kg

Size Similar to Humans

• A reconstruction of the skull of Homo erectus– a widely

distributed species – whose remains

have been found in Africa, Europe, India, China, and Indonesia

Skull of Homo erectus

• The archaeological record indicates – that H. erectus was a tool maker

• Furthermore, some sites show evidence – that its members used fire and lived in caves– an advantage for those living in more northerly

climates

H. erectus Was a Tool Maker

Homo erectus Using Tools

• Re-creation of a Pleistocene setting in Europe – in which members of Homo erectus are

– using fire and stone tools

• Currently, a heated debate surrounds the transition– from H. erectus to our own species Homo sapiens

• “Out of Africa" view– early modern humans evolved from a small African

colony– offspring then migrated from Africa and populated

Europe and Asia, driving the earlier hominid populations to extinction

The "Out of Africa" View

• “Multiregional" view– early modern humans did not have an isolated

origin in Africa– established separate populations throughout

Eurasia

• Occasional contact and interbreeding – enabled our species to maintain its overall

cohesiveness– still preserving the regional differences in people

we see today

The "Multiregional" View

• Regardless of which theory turns out to be correct, – our species, H. sapiens, most certainly evolved

from H. erectus

Homo sapiens Evolved From H. erectus

• Neanderthals– inhabited Europe and the Near East – 200,000 to 30,000 years ago

• Some paleoanthropologists :– as a Neanderthals are a subspecies of our own

species (Homo sapiens neanderthalensis)– Others: separate species (Homo neanderthalensis)

Neanderthals

• Main difference between Neanderthals and present-day humans is in the skull– Neanderthal skulls were long and low – heavy brow ridges, a projecting mouth, and a weak,

receding chin

• Their brain was slightly larger on average – than our own, and somewhat differently shaped

Neanderthals Difference

Neanderthal Skull• Reconstructed

Neanderthal skull

• The Neanderthals

were characterized • by prominent heavy

brow ridges and weak chin

• Given the specimens from more than 100 sites– we now know Neanderthals were not much

different from us, only more robust

• Europe's Neanderthals were the first humans – to move into truly cold climates– enduring miserably long winters and short

summers – as they pushed north into tundra ecosystems

First Humans in Cold Climates

Burial Ceremony in a Cave

• Archaeological evidence indicates – Neanderthals lived in caves – and participated in ritual burials– as depicted in this painting of a burial ceremony

– such as occurred approximately 60,000 years ago – at Shanidar Cave, Iraq

• About 30,000 years ago– humans closely resembling modern Europeans – moved into the region inhabited by the

Neanderthals and completely replaced them

• Cro-Magnons– successors of the Neanderthals in France– 35,000 to 10,000 years ago– huge advances in development of art and

technology

Cro-Magnons

• Cro-Magnons were cave painters

• Using paints made from manganese and iron oxides– painted hundreds of scenes on the ceilings and

walls of caves in France and Spain– many of them are still preserved today

Cave Painters

• Cro-Magnons were very skilled cave painters

– Painting of a horse – from the cave of Niaux, France

Painting From a Cave in France

• With the appearance of Cro-Magnons, – human evolution has become almost entirely

cultural rather than biological

• Humans have spread throughout the world – by devising means to deal with a broad range of

environmental conditions

Cultural Evolution

Summary

• Aegyptopithecus 32 Ma (ancestral hominid – primate)– Somewhat developed forehead

• Australopithecus 5 Ma (early hominids)– Afarensis (Lucy) 4 Ma, bipedalism, still tree climbers, small skull– Africanus 2-3 Ma slightly larger brain

• Homo habilis 2 Ma– Larger brain, less pronounced brow, rounder head, smaller face– Use of stone tools

• Homo erectus 500 K-2Ma– Larger brain and body– Longer skull, large brow ridges

• Homo sapiens neanderthalensis 200 K– Large brains and bodies, lack of frontal lobes?

• Homo sapiens sapiens (cro-magnon) 90 K– Anatomically similar to humans

Climate in Human History

• Peak of glaciation 18 Ka

• Present interglacial began 10 Ka

• Climatic Optimum

– 6-7 Ka

– First great civilizations in Middle East

– Some collapsed 3 Ka when climate changed

• Subatlantic Deterioration

– 2.5 Ka

– Reflected in art and invasions

• Drought and famine

• Location of settlements

• Exploration

• Medieval Warm Period began ~950 A.D.

• Little Ice Age 1550-1850 A.D.

Climate in Human History

Vikings

• Settled Greenland and Iceland during Medieval Warm Period

• During Little Ice Age, Greenland was abandoned and Iceland struggling

• Ice blocked trade routes, cold weather caused poor harvests

• Fish moved southward

Climate reflected in art

• Little Ice Age at its peak during 2nd epoch

www2.sunysuffolk.edu/mandias/lia/little_ice_age.html

Recent History

• Two centuries of warm, mild climate

• Continual drying of northern Africa

• Interglacial should be coming to an end – will humans prolong it?