NOTES:

Ch 34 -

Mammals &

Primate /

Human

Evolution

(34.7-34.8)

Class: MAMMALIA● Mammals possess unique

derived characteristics:

1) Provide young with milk

(mammary glands)

2) Internal fertilization; some

embryo development

within uterus before birth

3) Hair

Class: MAMMALIA● Mammals possess unique

derived characteristics:

4) Endothermic (high

metabolic rate)

5) Larger brain (than other

vertebrates of similar size)

6) Differentiated teeth

Mammals…● Most mammals are EUTHERIANS (a.k.a.

“placental” mammals”)

-highly developed at birth

-most are terrestrial, but some are marine

-important grazers and browsers in terrestrial

ecosystems

● Primates have been present for

65 million years and are defined

by shared derived characteristics

shaped by natural selection for

living in trees:

● limber shoulder joints

● dexterous hands

● sensitive fingers with nails

(not claws)

● eyes close together

● excellent hand-eye coordination

● parental care with usually single

births and long nurturing

● complex social behavior

(b) Old World monkey: macaque(a) New World monkey:spider monkey

(a) Gibbon

(b) Orangutan

(c) Gorilla

(d) Chimpanzees

(e) Bonobos

● Most anthropologists believe that

humans and apes diverged from a

common ancestor 6-8 million years ago

ANCESTRALPRIMATE

Time (millions of years ago)

60 50 40 30 20 10 0

Lemurs, lorises,and bush babies

Tarsiers

New World monkeys

Old World monkeys

Gibbons

Orangutans

Gorillas

Chimpanzeesand bonobos

Humans

An

thro

po

ids

(d) Chimpanzees

(e) Bonobos

Derived Characters of Humans

● A number of characters distinguish humans from

other apes

-Upright posture and bipedal locomotion

-Larger brains capable of language, symbolic

thought, artistic expression, the manufacture

and use of complex tools

-Reduced jawbones and jaw muscles

-Shorter digestive tract

The Earliest Hominins

● The study of human

origins is known as

paleoanthropology

● Hominins are more

closely related to

humans than to

chimpanzees

● Paleoanthropologists

have discovered fossils

of about 20 species of

extinct hominins

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Mil

lion

s of

yea

rs a

go

Australo-pithecusanamensis

Kenyanthropusplatyops

Australopithecusafricanus

Paranthropusboisei

Paranthropusrobustus

Homoergaster

Homoneanderthalensis

Homosapiens

Homo erectus

Homo rudolfensisHomo

habilis

Australopithecusgarhi

?

Australopithecusafarensis

Ardipithecus ramidus

Orrorin tugensis

Sahelanthropustchadensis

● Misconception: Early hominins were

chimpanzees

**Correction: Hominins and chimpanzees

shared a common ancestor

● Misconception: Human evolution is like a

ladder leading directly to Homo sapiens

**Correction: Hominin evolution included

many branches or coexisting species,

though only humans survive today

The First Humans:

Australopiths

● Australopiths are a paraphyletic assemblage of

hominins living between 4 and 2 million years ago

● Some species, such as

Australopithecus

afarensis walked

fully upright

(a) The Laetoli footprints (b) Artist’s reconstruction of A. afarensis

The First Humans:

Australopiths

The First Humans:

● Australopithecus africanus:

– walked upright; humanlike teeth and hands

– brain was about 1/3 size of modern humans

– 4 million years ago; existed for 3 million yrs.

Chimpanzee Australopithecus africanus Homo sapiens

● Australopithecus afarensis (“Lucy”)

– upright posture

– evidence of coexistence with A. africanus for

about 1 million years

● Australopithecus anamensis: about 4 m.y.a.

● Ardipithecus ramidus: about 4.4 m.y.a.

● hominids walked upright for two million

years without a substantial increase in

brain size!

● this posture may have freed the hands

for other things such as gathering food

or caring for infants

Early Homo

● The earliest fossils placed in our genus Homoare those of Homo habilis, ranging in age from about 2.4 to 1.6 million years

● Stone tools have been

found with H. habilis, giving

this species its name,

which means “handy man”

Homo habilis● enlargement of brain is evident

in fossils dating back to about

2.4 -1.6 m.y.a. (650 cc vs. 500

cc)

● simple stone tools found with

larger-brained fossils

● coexisted with A. africanus for

almost 1 million years

(A. africanus was an

evolutionary “dead end”)

adult cranial capacity

(range in cm3)

•Chimpanzees

300-500

•Australopithecines

400-530

•early transitional

humans 500-750

•modern humans

900-2300

● Homo ergaster was the first fully bipedal, large-

brained hominid

● The species existed between 1.9 and 1.5 million

years ago

● Homo ergaster shows a significant

decrease in sexual

dimorphism (a size

difference between

sexes) compared with

its ancestors

Early Homo

Homo erectus & descendants● taller and larger brain than H. habilis

(1200 cc)

● first hominid to migrate out of Africa

● 1.8 m.y.a. to 250,000 years ago

● H. erectus remains have

been found on other

continents

● diet shifted to include a

larger portion of meat

● intelligence allowed them

to survive in colder

climates (lived in huts or

caves, built fire, wore

clothing, designed more

refined tools)

**best known descendants

of H. erectus are

Neanderthals!

-lived in Europe, Middle

East, & Asia

-they were thick-boned with

a larger brain, they

buried their dead, and

they made hunting tools

-350,000 to 28,000 years

ago

The Origin of Modern Humans

(2 theories):

1) Multiregional

Model

2) Monogenesis

Model

(“Out of Africa”

model)

1) Multiregional Model

● proposes that modern humans evolved

in parallel along the same lines in

different parts of the world

*if true, then…

● the geographic diversity of humans

originated between 1-2 m.y.a. when H.

erectus first spread from Africa to other

continents

2) Monogenesis Model

(“Out of Africa” model)

● proposes that modern humans evolved from the

H. erectus group(s) that stayed in Africa; they

then dispersed from Africa, displacing the

Neanderthals and other hominids (suggests the

Neanderthals were NOT ancestors of modern

humans since they coexisted and were probably

evolutionary dead ends)

*if true, then…

● the geographic diversity of humans developed

within the last 100,000 years

● Mitochondrial DNA (mtDNA) studies

support the monogenesis model.

Homo Sapiens

● Homo sapiens appeared in Africa by 195,000

years ago

● All living humans are descended from these

African ancestors

Homo Sapiens

● The oldest fossils of Homo sapiens outside Africa

date back about 115,000 years and are from the

Middle East

● Humans first arrived in the New World sometime

before 15,000 years ago

● Homo sapiens

were the first group

to show evidence

of symbolic and

sophisticated

thought

Homo Sapiens

Cultural

Evolution:

● the basis of culture is learning from the

experiences of earlier generations

● transmission of information is by written

and spoken language

Cultural Evolution & Learning

*Cultural learning facilitated spread of

domesticated plants and animals

Human societies converted from hunters &

gatherers to PASTORAL (herding large

animals) and AGRICULTURAL

Human Population Growth:

Three phases:

1) Tool use: lasted about

1 million years

-POP. = 5 million ppl.

2) Domestication of plants

& animals: lasted about

8,000 years

-POP. = 500 million ppl.

Human Population Growth:

3) Industrial Revolution: started about 300

years ago

-CURRENT POP. = 7.0 billion ppl.

-EST. POP. by 2050 = 11 billion ppl.