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ancestors of humans were becoming distinct from the
apes (Figure 23.17A). By 3.9 million years ago a clearly
bipedal hominin, Australopithecus afarensis, lived in Africa.
The individual whose skeleton is shown in Figure 23.17B,
dubbed “Lucy,” had a slight build, unlike some other Afri-
can hominins. About 200,000 years earlier, at what is now
Laetoli, Tanzania, A. afarensis walked across fresh volcanic
ash during a light rain, which turned the ash to quick-
drying cement. We know little about how various homi-
nins were related or if they used tools, but the footprints at
Laetoli (Figure 23.17C), as well as fossil hip and limb bones,
confirm that they walked upright.We all come from Africa
By a little over 2 million years ago, ancient species of
humans—members of the genus Homo—were living in
woodlands of eastern Africa. One was Homo habilis (Fig-
ure 23.17D). Compared to other hominins, these early
humans had a larger brain, smaller face, and thickly enam-
eled teeth. They ate both plant and animal foods and used
tools. Fossil hunters have found many stone tools dating to
the time of H. habilis.
Divergence produced Homo erectus (Figure 23.17E). This
species is considered the likely ancestor both of mod-
ern humans and of the Neanderthals mentioned in Sec-
tion 23.7. The name Homo erectus means “upright man.”
Fossil finds reveal that by about 500,000 years ago, indi-
viduals descended from H. erectus began leaving Africa. In
2003, fossils of early humans that date to 18,000 years ago
turned up on the Indonesian island of Flores. The species
was named H. floresiensis (Figure 23.18), but some research-
ers believe the fossil bones may be from modern humans
who suffered a nutritional deficiency.emergence of early Humans
Figure 23.17 Animated! We have fossil evidence of African
hominins and early humans. A Representative fossils of African
hominins. B Remains of “Lucy” (Australopithecus afarensis),
who was a hominin. C At Laetoli in Tanzania, Mary Leakey
found these footprints made 3.7 million years ago. D A skull of
H. habilis (see also Figure 23.3B), an early species of human.
E A skull of H. erectus, a relative of modern humans that walked
upright. (A left: HO/AFP/Newscom; A right: © Friedrich Saurer/Alamy; B: Dr. Donald
Johanson, Institute of Human Origins; C: John Reader/Science Source; D: Colin Keates/
Dorling Kindersley/Getty Images; E: Pascal Goetgheluck/Science Source)Sahelanthropus tchadensis
7–6 million years agoAustralopithecus afarensis
3.6–2.9 million years agoADH. habilis
1.9–1.6 million years agoEH. erectus
1.9 million to 53,000 years agoB C23.9
n By 36 million years ago tree-dwelling primates called
anthropoids had evolved in tropical forests. One or more
types were on or very close to the evolutionary road that
would lead to monkeys, apes, and humans.Between 23 and 5 million years ago, apelike forms—the
first hominins—evolved and spread through Africa, Asia,
and Europe. At that time, shifts in Earth’s land masses and
ocean circulation caused a long-term change in climate.
Lush African forests began to give way to open wood-
lands and later to grasslands. Food became harder to find.
In these new circumstances, most of the hominins went
extinct. A survivor was the common ancestor of two lin-
eages that arose by 7 million years ago. One gave rise to the
great apes, and the other to the first hominins.
Early hominins lived in central Africa
Sahelanthropus tchadensis may have been a hominin. It
lived in central Africa 6 to 8 million years ago, when the
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