What Traits Characterize Humans?• Bipedal Locomotion

– Involves modifications of pelvis, femur, and backbone– Various hypotheses regarding benefits, including free hands (vs. knuckle-

walking and brachiation of great apes)

• Large Brain Size – Requires omega fatty acids – high levels in marine organisms, nuts, marrow

• The Making and Use of Complex Tools– Earliest stone tools produced by chipping flakes from a rock; oldest dated at

~ 2.5 mya (Oldowan Stone Tools) – Opposable thumbs allow fine control and tight grips; include thick meta-

carpals with broad heads for muscle attachment; three muscles not found in chimpanzees

• Language and Cultural Evolution– Capacity for language is innate in humans (ex., children born deaf create

languages)– Modifications of larynx allow more tongue movement and great diversity of

vocalizations (trade-off is greater chance of choking); hyoid bone of Neanderthals virtually identical to that of present-day humans

– Memes: ideas that can be disseminated via oral or written means, subject to modifications and non-genetic descent (impart information, cultural analogue to genes)

Fig. 34-37Lemurs, lorises,and pottos

Tarsiers

New World monkeys

Old World monkeys

Gibbons

Orangutans

Gorillas

Chimpanzeesand bonobos

Humans

0102030405060

Time (millions of years ago)

ANCESTRALPRIMATE A

nth

rop

oid

s

What are Some Notable Fossil Hominids?• Pre-australopithecine: ~ 7 - 5 million years ago (mya)

– Sahelanthropus tchadensis: 6-7 mya (Chad); found in lake deposits from ancient Lake Chad

– Orrorin tugenensis: ~ 6 mya (Kenya); recent evidence for bipedalism based on CT scan of femur neck (controversial)

• Australopithecines: projecting faces; braincases < 550 cm3

– Australopithecus africanus: ~ 2.8 - 2.4 mya; first hominid fossil found in Africa (“Taung Child”); discovered in coastal South

African cave by Raymond Dart in 1925; more specimens found nearby in 1930s - 1940s

– Australopithecus afarensis (incl. “Lucy”): ~ 3.9 - 3.0 mya (Tanzania and Kenya); footprints in volcanic ash dated at 3.6 mya

• Early Humans: apparently coexisted with robust australo-pithecines in Africa

– Homo erectus (= H. ergaster): ~ 1.8 - 0.4 mya; widespread through Africa and Asia (ex. “Java man”); large braincase (> 850

cm3); most likely ancestor of more modern humans – Homo neanderthalensis: ~ 0.3 - 0.03 mya; found in Europe – Early Homo sapiens (incl. Cro-Magnon): ~ 0.1 mya - present;

present-day average braincase = 1200 cm3; Cro-Magnon Man (30,000 ya) buried with animal bones, jewelry, and tools

Fig. 34-40

Homoerectus

Homohabilis

Homosapiens

Homoneanderthalensis?Homo

ergaster

Paranthropusrobustus

Paranthropusboisei

Australopithecusafricanus

Australopithecusgarhi

Australopithecusafarensis

Sahelanthropustchadensis

Orrorin tugenensis

Ardipithecusramidus

Australo-pithecusanamensis

Kenyanthropusplatyops

HomorudolfensisM

illio

ns

of

year

s ag

o

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

Fig. 34-41

(c) An artist’s reconstruction of what A. afarensis may have looked like

(a) Australopithecusafarensis skeleton

(b) The Laetoli footprints