Chapter 11

Primates and Human Evolution

Primate Characters• Grasping hands and feet with thumb and big

toe often opposable

• Sensitive pads on fingertips and nails instead of claws

• A mobile shoulder joint, especially in humans

• Large braincase and a postorbital bar

• Flattened face with eyes rotated forward for stereoscopic vision

• Usually have one offspring at a time

• Females have only two mammary glands

Anthropoid Origins• Anthropoid (“human-like”)

primates were thought tohave originated in Africa.

• Recent finds from the early Eocene of China and Thailand (above) have challenged this view because they are older.

• Anthropoids are distinct in having rounded nostrils (not slit-like as in prosimians), usually large canines, molar-like premolars, and broad square molars.

Miocene Apes• Proconsul is the best-

known early ape, early Miocene of Kenya.

• Proconsul is designed for diverse locomotion styles (quadrupedal running, standing upright, swinging from branches) and could probably swing a stick for defense.

Proconsul

Hominoid Relationships

Pongidae (ape family) has been eliminated as a paraphyletic group, and Hominidae (human family) has been expanded to include most apes. Note in the right diagram that no common ancestors are known!

Hominidae – great apesHylobatidae – lesser apes

Classification of Apes and HumansSuperfamily Hominoidea• Family Hylobatidae – gibbons

– Smaller tree-climbing apes

• Family Hominidae

– Subfamily Ponginae – Orang-utans

• Slow climbers and brachiators

– Subfamily Homininae

• Terrestrial quadrupeds – chimps and gorillas

• Infrafamily Hominini – Terrestrial bipeds – humans

– Monophyletic group of humans and their closest relatives

• Apes arose in the Miocene of Africaas grasslands developed there,have short 5‑cusp molars

• Early-middle Miocene: Dryomorphs

– Large canines, Africa to Eurasia

• Middle-late Miocene: Ramapithecines

– Small canines, very diverse, Africa to Asia

• Pliocene: poor fossil record leaves many questions about hominid relationships, including the origins of living groups of apes

Apes

Baboon

Chimp

Apes• It was long believed that Ramapithecus was

the first human and that the human/ape split occurred 15 M.Y. ago. DNA and protein similarities, however, suggested a mere 5 M.Y. ago split, with man, chimp, and gorilla being equally similar. Discovery of more skeletal material suggested that Ramapithecus is an orang-utan.

• Gorillas and chimps have no definite fossil record, so tracing their ancestry is difficult.

Late Miocene ApesSivapithecus (=Ramapithecus) of China region Modern human

Jaw and molars of Sivapithecus showing “Y” and cusp pattern

Lower jaw of Gigantopithe-cus (late Miocene of India and Pleistocene of China)Hand of Dryopithecus

Chimp

Humans and Upright Posture

Foot flat with straight toes for plantigrade walking

Loss of opposable toe in foot

Grasping hand

Gorilla

Walking on knuckles

Modifications for Bipedalism

• Skull with ventral foramen magnum

• Backbone develops an S-curve

• Pelvis short with bowl-shaped ilium to support abdominal organs

• Hip joint faces downward and sideways

• Long, slender leg bones

• Knee forms a straight hinge for standing

• Foot a flat platform with non-opposable toes

Reasons for Bipedalism

• Ability to stand tall for a better view

• Freeing up the hands to use tools

• Faster or more efficient locomotion

• One theory is that forest-dwelling apes became restricted to west Africa where they gave rise to chimps and gorillas, while humans arose as an adaption to the open grasslands in east Africa.

Brain First Theory• The early popular theory was that

the big brain was required for tool use, so it came before bipedalism.

• This was confirmed by a skull at Piltdown, England, with a large braincase but primitive jaws (a).

• Piltdown man turned out to be a hoax (a human cranium planted with an orang-utan jaw).

• Australopithicus found in Africa (b) disproved the brain first theory with its small brain and bipedalism.

Piltdown Man• Discovered 1912 near Piltdown,

East Sussex, England

• Exposed as a fraud in 1953

• Parts of human skull and orang-utan jaw etched with acid and buried at an excavation site.

Why was the hoax so readily accepted by England’s experts?

Piltdown ManMost human fossils hadbeen found in Africa.

There were racistviews about Africa.

It was a relief to findevidence of humanevolution in Europe.

Though the skull wasfrom a modern human,Piltdown was consideredintermediate in brain sizebetween Homo erectusand Neanderthal Man!

Neoteny is the evolutionary process where juvenile traits are retained into adulthood.

Adult Chimp

Juvenile Chimp

Juvenile Chimp

Adult Human

Juvenile Human

Human evolution may be a case of neoteny. Enlargement of the human brain could have been accomplished by retaining the juvenile proportions of an ape. This could also explain the loss of hair in humans. But it fails to explain our large legs.

Early Human Fossils• Orrorin – teeth, jaw fragments,

broken limb bones that suggestbipedalism, 6 M.Y. old

• Sahelanthropus – distortedcranium (at right) with foramenmagnum that suggests bipedalism, 6 M.Y. old

• Ardipithecus – teeth, skull fragments, and limb bones from several individuals with somewhat large canines, thin tooth enamel, and clear evidence of bipedalism, 5.8 to 4.4 M.Y. old

• Praeanthropus – Lucy (most of skeleton found in 1974) and other bones and teeth, 4.1 to 2.9 M.Y. old

Praeanthropus walked fully upright

Early hominids had the distinct human pelvis for upright walking. Fossil trackways also demonstrate full bipedality.

Evolution of Human Characters

Chimp

Ardipithecus

Praeanthropus

Ape Praeanthropus Modern human

Ape

Modern human

FingersSkeleton of Lucy (Praeanthropus), the most complete early hominid skeleton

Palate of Lucy

Legs

Australopiths• All previously included in genus Australopithecus

• Praeanthropus – small primitive forms such as Lucy (P. afarensis) with strong sexual dimorphism

• Australopithecus – advanced gracile australo-piths that probably gave rise to Homo

• Paranthropus – robustaustralopiths with broad facesand massive jaws (at right)

• The last two have smallcanines and no diastema

Human Timeline

Later Australopiths

• Australopithecus africanus (gracile,3.0-2.3 M.Y. ago)

• Paranthropus robustus (robust, 1.9-1.6 M.Y. ago)

• Paranthropus boisei (robust, 2.4-1.3 M.Y. old)

Human Relationships

Hominid Species

Hominid species Age Brain size Height

Praeanthropus afarensis 4.0‑3.0 M.Y. 380‑450 cc 1.2 m

Australopithecus africanus 3.0‑2.3 M.Y. 380‑450 cc 1.4 m

Paranthropus robustus 1.9‑1.6 M.Y. 380‑450 cc 1.5 m

Paranthropus boisei 2.2‑1.2 M.Y. 380‑450 cc 1.5 m

Homo habilis 2.0‑1.6 M.Y. 630‑700 cc 1.3 m

Homo erectus 1.6‑0.3 M.Y. 800‑1300 cc 1.7 m

Homo sapiens 0.1‑0.0 M.Y. 1000‑2000 cc 1.8 m

- Neanderthal Man (replaced Homo erectus, large brow ridges, elaborate burials)

- Cro‑Magnon Man (replaced Neanderthal 40,000 yr, made cave art in France/Spain)

- Modern Man (developed from earlier forms, domesticated plants and animals)

Early Species of Homo• Homo habilis (“handy man”)

was discovered in OlduvaiGorge, Kenya, in the 1960sby Louis Leakey and has amuch larger brain than theaustralopiths.

• Homo rudolfensis is a possiblesecond species from Kenyawith a larger brain but other more primitive features (skull above).

• Without the enlarged brain both would better be classified as australopiths. Both are 2.4-1.5 M.Y old.

Earliest Homo (Africa)• Homo habilis and Homo

rudolfensis represent one or two species of early Homo from Kenya.

• Homo probably evolved from the Australopithecus africanus.

• The primary feature is a large increase in cranial size over Australopithecus.

• Homo coexisted with robust Australopithecus for about a million years.

Homo habilis

Homo erectus – Exiting Africa

• The earliest Homo erectus (or H. ergaster) (a) dates to 1.9 M.Y. ago and has a brain size of 830 cm3 but retains heavy jaws and brow and lacks a chin.

• More specialized Homo erectus material is found throughout Eurasia dating 1.9-0.5 M.Y. ago along with Acheulean hand axes (b-d).

Prior to 2 mil-lion years ago humans were restricted to eastern Africa.

Evolution of Homo

Peking Man(Homo erectus)

Common in Africa and Asia

Neanderthal Man(Homo sapiens neanderthalensis)

Common in Africa and Europe

Stone ToolsNeanderthal

(Homo sapiens)

Homo erectus

Homo habilis

Neanderthal Man

• Neanderthal Man (a, c) is an archaic form of Homo sapiens that branched off half a million years ago and lived till 30,000 years ago.

• Compared to modern man (b) they had a similar brain size but differences in head shape. Invading Cro Magnon man may have killed them.

Modern Man

• Found in Africa and Israel dating back 100,000-120,000 years ago (skull above)

• Spread into Europe 40,000 years ago (Cro-Magnon Man), but no evidence they mixed with Neanderthals, and to Australia at the same time

• DNA evidence shows that the latest common ancestor of all living humans lived about 200,000 years ago in Africa (“Mitochondrial Eve”).

Dispersal of Modern Humans

The Americas were the last continents to be colonized, with the oldest well-documented site in Chile! The Ice-Age Bering Land Bridge is the obvious route, but there’s debate whether they tra-veled inland (big game hunters) or along the coast (fishermen).

Humans arrived in the Americas about 14,000 years ago.

• The old theory is that humans traveled between the ice sheets of Canada in what is called the “ice-free corridor.”

• An newer theory is that they came down the Pacific Coast by boat (supported by Dr. Heaton’s Alaska research).

LGM Ice Cover

Cast of human mandible in

On Your Knees Cave (9,800 yr

B.P.)

By Erik Hill,

Anchorage Daily News

Archaeological Excavation at

On Your Knees Cave

Many bifaces, microblades, bone tools, and cultural charcoal beds were found inside and outside the cave.

Common mammals from On Your Knees Cave

Middle Wisconsin 50,000-24,000 yr B.P.

Brown bear

Black bear

Arctic fox

River otter

Harbor seal

Steller’s sea lion

Caribou

Saiga (or goat)

Long-tailed vole

Hoary marmot >

Heather vole >

Brown lemming >

Last Glacial Maximum 24,000-13,000 yr. B.P.

Arctic fox

Red fox

Ringed seal

Harbor seal

Steller’s sea lion

Maybe

Brown bear

Black bear

Otter/Mink

Caribou

Postglacial 13,000 yr B.P.-present

Brown bear

Black bear

Arctic fox

Red fox

River otter

Steller’s sea lion

Caribou

Black-tailed deer

Long-tailed vole

Human

Bold indicates index species

The Northwest Coast• The coast had more exposed land area during the

Last Glacial Maximum than previously thought.• The period of maximum ice cover was very brief.• The coast provided an easy means of transportation• The coast had a more moderated climate then the

interior.• The coast had a rich supply of seafood.• Making a living along the coast required similar

culture at all latitudes, whereas traversing the interior requires diverse adaptations.

• This could explain the rapid colonization of North and South America.