Chapter 13: Human Evolution

What are the major adaptations of primates?

1. Agility in trees

2. Large brain + acute daylight vision

3. Parental care

Cranial/ face features of primates

• postorbital bar

• strut between orbit and lower temporal fenestra (= fossa) which is absent in related mammals

• large auditory bulla

• primates → larger brain in proportion to body size than all other terrestrial mammals

• eyes generally large and close together at face front

• snout reduced

• flattened face → look forwards, overlap between fields of vision = stereoscopic or 3D sight possible

Features of primates related to parental care

• usually one baby at a time

• 2 mammary glands

• late sexual maturity

• high parental investment

When did primates radiate

• radiated in Paleocene and Eocene

• modern groups radiated extensively in early Eocene

• older records from the Cretaceous are doubtful, although molecular evidence suggests that the order might have originated in the latest Cretaceous

What 2 clades are primates divided into?

• Strepsirrhini

• Haplorhini

Strepsirrhini

lemurs and lorises

Haplorhini

tarsiers, monkeys and apes

What are Anthropoidea?

• ‘higher’ primates => monkeys and apes

• includes the extinct Eosimiiformes plus the (extant) Simiiformes

Platyrrhines

• New World monkeys

• literally ‘broad noses’

• broadly spaced nostrils that face forwards, and some have a prehensile tail

Catarrhines

• Old World Monkeys + apes

• have narrow snouts and non‐prehensile tails

• literally ‘hooked noses’

Features of Anthropoids

• have the rounded nostrils of all haplorhines as well as large canines that occlude with the opposite canine and first premolar, the premolars are rather molar‐like, and the molars are broad and square.

When did anthropoids originate?

Late Paleocene

Locomotory adaptations of anthropoids

• most being capable of walking quadrupedally along branches, and leaping from tree to tree

• larger forms were probably slower moving

The visual system of anthropoids

• cornea smaller → longer focal length and improved visual acuity

• reduced cornea = less light into eye → adaptation arose in diurnal species

• Colour vision

• Catarrhines (Old World monkeys, apes, humans) stand out as having three cone types (other mammals, including other anthropoids have two cone types).

• Catarrhines again are unique in their substantial loss of the sense of smell

When did New World monkeys split from Old World monkeys?

• split from old world monkeys in Eocene

• reached S.America from Africa

• raft → accident

When did the crown group Simiiformes split?

• the crown‐group Simiiformes split into Old and New World monkeys in the middle or late Eocene

• The clade split early into the superfamily Cercopithecoidea, the Old World monkeys and Hominoidea, the apes and humans

What are the Hominoidea?

• Apes

• include gibbons and orangutans of Southern and Eastern Asia, gorilla and chimpanzees from Africa and humans

Features of the genus Proconsul (early ape)

• could move on the ground on all fours and run quadrupedally along heavy branches.

• The elbow and foot anatomy of Proconsul is fully ape‐like, but the head is monkey‐like, with small molar teeth and long projecting canines

• Its diet was probably soft fruit

• regarded as a true ape →absence of tail and relatively large brain size + ape-like teeth and modifications to strengthen the elbow joint for brachiation (arm swinging)

What are the Hominidae?

• great apes

What are the 2 subfamilies of Hominidae?

1. Ponginae → the three species of orangutan and its fossil relatives

2. Homininae → five species of modern chimps, gorillas, and humans and their fossil relatives

Why is the split in Hominidae important?

• marks a divergence in modes of locomotion from a generalized tree‐climbing ancestor

• the orangutans specialized in suspension (brachiation) and slow climbing

• the African great apes specialized in terrestrial quadrupedalism (chimps, gorillas) and bipedalism (humans).

What are the 2 main characters that set humans apart from other apes?

bipedalism and large brain size

Anatomical changes for bipedalism/ upright posture

• foot became a flat platform structure with a non‐opposable big toe and straight phalanges in the toes

• apes and monkeys have a grasping foot with curved phalanges and an opposable big toe

• the angle of the human knee joint shifts from being slightly splayed to being a straight hinge, and all the leg bones are longer

• hip joint faces downwards and sideways and the femur has a ball‐like head that fits into it

• pelvis as a whole is short and bowl‐like as it has to support the guts, and the bowl-like to support the guts

• backbone adopts an S-shaped curve

• Bipedalism → changes to skull as it is sat on top of vertebral column instead of at the front

• Occipital condyles and the foramen magnum, the skull opening through which the spinal cord passes, are placed beneath, rather than behind, the skull roof

What is the backbone like in apes?

pelvis is long, backbone = C-shaped to brace the weight of the trunk between the arms and legs

Adaptations to life in open habitat

• stand upright → spot predators

• bipedal → carry objects/ food

Savanna hypothesis/ East Side Story

• the forest‐dwelling Miocene apes became restricted to the west of Africa, where they gave rise to the gorillas and chimps, after the Great Rift Valley began to open up, and the apes that remained in the east had to adapt to life on the open grasslands

Evidence/ dates for bipedalism

• hominin skeletons 6-4 Ma and trackways 3.75 Ma

• Habitual bipedalism probably arose 9–6.5 Ma in the hominin line, when it split from the African apes

Increased brain size in humans

• increase in relative brain size that occurred much later, only about 2 Ma with the origin of the genus Homo

• early bipedal humans still had rather ape‐like heads with brain sizes of 400–550 cm3, similar to apes, and by no means comparable with modern humans, who have a brain size of 1000–2000 cm3 (mean 1360 cm3), a value approached by some examples of 500,000‐year‐old fossil Homo

Changes to anatomy as a result of increased brain size

• back of head enlarged

• face less projecting and placed largely beneath front of brain

• the rounded tooth row with a continuous arc of teeth and no gap (diastema) between the incisors and canines (see Figure 13.10j) is a human character.

What arose first: bipedalism or enlarged brains?

Present fossil evidence then suggests that human evolution followed a ‘locomotion‐first’ pattern, with bipedalism arising before 6 Ma and the enlarged brain less than 2 Ma.

Molecular estimates for the split of humans from chimp

8 - 5 Ma

Lucy scientific name

Australopithecis afarensis

How old is Lucy?

• Lucy is dated as 3.2 Myr old and Au. afarensis specimens range from 3.7 to 3.0 Myr in age

• Pliocene

Features of Australopithecus

• individuals are 1–1.2 m tall, with a brain size of only 415 cm3 and a generally ape‐like face

• although the brain was ape‐like in size, there is evidence for prolonged growth from baby to adult, a feature of humans

• other plesiomorphic characters include a small diastema, long arms and rather short legs and curved finger and toe bones

• sexually dimorphic

• curved bones → grasping branches

Diet of the first human species

• leaves, fruits and nuts from trees

• foods derived from grasses → sedges and succulents

• take advantage of food resources

How did the later Australopithecines differ from Australopithecus

• flattening of the face

• loss of the diastema

• small canine teeth

• molars and premolars are more massive + covered with thick layers of enamel → adaptation to tough plant food diet

When did the Australopithecines live?

in Africa through the late Pliocene and earliest Pleistocene from about 3.6–1.1 Ma

Oldest possible Transitional Hominins

• Homo habilis and H. rudolfensis

• Ethiopia, 2.8-2.75 Ma

Features of H. habilis and H. rudolfensis

• large brain, in the range of 630–700 cm3

• hands had the manipulative ability to make tools

How are H. habilis and H. rudolfensis distinguished?

• H. rudolfensis has a larger mean brain size but appears to be ape‐like in other skull features (smaller ‘eyebrow ridge’, palate large)

• The remains of H. habilis and H. rudolfensis are dated as 2.4–1.5 Myr old

Origin of Homo erectus

~ 2 Ma

Features of Homo erectus

• specimen found had brain size of 830 cm3

• skull is more ape‐like than H. sapiens because it still has large eyebrow ridges and a heavy jaw with no clear chin

• skeleton seems largely modern and fully bipedal in adaptations

• BUT might be separate species ⇒ H. ergaster

When did H. erectus leave Africa?

~ 1.9 Ma

Example of a Middle Pleistocene Hominin

Homo heidelbergensis

Features of Neanderthals

• larger brain capacity (mean 1450 cm3) than many modern humans (mean 1360 cm3)

• heavy eyebrow ridges, massive jaws and large teeth compared with modern H. sapiens

• robust, compact body

Neanderthal culture

• culturally advanced

• variety of tools made from wood, bone and stone

• spearheads, hand axes, scrapers for removing fat from animal skins

• art → engraving on stones/ bone

• made clothes from animal skins, used fire extensively, lived in caves or bone and skin shelters and perhaps even had rituals

When did Neanderthals disappear

• 50,000- 35,000 years ago

• competition with invading peoples

• modern European and Asian DNA contains only 1–4% Neanderthal genes

When did modern H. sapiens originate?

~300,000 years ago

Features of modern Homo sapiens

• modern face, flattened and with little sign of the prognathism (extended snout) seen in Neanderthals and H. heidelbergensis, which are of the same age.

• However, the occipital (posterior) part of the cranium extends back further than in modern humans and the molars are larger, both being features of more archaic humans

H. Sapiens in the Second Migration out of Africa

• likely several migrations out of Africa ~100,000 years ago

• Then, modern H. sapiens entered Europe as the ice retreated, from 57,000 years ago, and seemingly drove the Neanderthals back to the northern latitudes and eventually to complete extinction

• Modern H. sapiens spread into Europe from 40,000 to 30,000 years ago

• truly worldwide from 70,000–40,000 years ago

Timing of the arrival of peoples to America

• Ice sheets retreated from the area of Beringia (Siberia and Alaska) and there was an ice‐free land bridge from Siberia to Alaska from 18,000 to 10,200 years ago.

• Hundreds of North American archaeological sites with tools of the Clovis industry date from 13,250–12,800 years ago, but a human occupation site at Monte Verde in southern Chile dates back to 14,500 years ago, and an older layer to 18,500 years ago

• Dates of archaeological sites in North America also show evidence for pre‐Clovis occupation of different parts of the continent by 14,955–13,495 years ago

• Ancient DNA evidence also confirms these dates → island hopped/ boats

• humans entered North America after the end of the last glacial maximum (LGM = 26,000-20,000)

Timings of major innovations in human evolution: Bipedalism

10 - 5 Ma

Timings of major innovations in human evolution: Enlarged brains

3 - 2 Ma

Timings of major innovations in human evolution: Stone Tools

2.6 Ma

Timings of major innovations in human evolution: Wide geographical distribution

2–1.5 Ma

Timings of major innovations in human evolution: Fire

1.5 Ma

Timings of major innovations in human evolution: Art

35,000 years ago

Timings of major innovations in human evolution: Agriculture and the beginning of global population increase

10,000 years ago