Building Modern
Humans
In the 1960s, Mary
Leakey found tools
from about 1.8
million years ago
in Olduvai Gorge.
These tools, called
Olduwan tools, are
attributed to Homo
habilis.
OLDOWAN TOOLS (left to right): end
chopper, heavy-duty scraper, spheroid
hammer stone (Olduvai Gorge); flake
chopper (Gadeb); bone point, horn core
tool or digger (Swartkrans).
These tools predated finds
of Homo habilis himself. In
the early 1960s, some
pieces of jawbone were
found.
Eventually, skull fragments
surfaced.
The brain of H. habilis was
about 30% larger than that
of Australopithecus,
although the skeleton was
otherwise similar.
The use of tools is significant because of what it implies about mental
ability.
Archaeologists date the Paleolithic (Old Stone Age) from this time.
From this point on, hominid evolution is characterized as much by its
tools as by anything else.
Homo habilis,
like its ancestors,
was an African
homind.
FIGURE 15.1 Hominid Relationships
Later hominids generally evolved in two directions—one a “robust” line that became extinct
about 1 million years ago, and the other the “gracile” line continuing down to modern
Homo sapiens (see also figure 14.6).
H. Habilis may have
developed a larger brain
and used it to develop
more sophisticated tools.
This likely produced a
more complex social and
hunting system.
This idea is called the
hunting hypothesis – the
idea that the need to kill
small animals led to
increased mental
abilities, group
interactions, and
aggressive behavior.
H. Habilis and the
related species H.
rudofensis and H.
ergaster account for
about a million years of
hominid evolution from
~ 2.5 mya to ~ 1.5
mya.
Homo habilis
Homo rudolfensis
Homo ergaster
The species that followed,
Homo erectus, was the first
to be found outside of
Africa.
From the neck down, H.
erectus was similar in stature
and anatomy to modern
humans.
Its brain was almost 50%
larger than that of H. habilis.
Homo erectus camp sites
show evidence of many
animal bones and many tools.
There is also some evidence
of fire, although their use of it
is uncertain.
In the late 19th Century, it
was widely believed that a
single, direct ancestor could
be found linking the apes
and the humans.
This is not true, but it
energized the search for
hominid fossils at the time.
FIGURE 15.2 “Missing Link” Fallacy
(a) A misreading of primate evolution led to the view that midway between modern apes
(such as orangutans, gorillas, chimpanzees) and modern humans there existed a direct,
intermediate ape that was a blend of ape and human traits. (b) As current phylogeny
shows, no such direct intermediate occurs, or is expected. Instead, apes and humans trace
their ancestry back along independent lineages to a common ancestor about 6 to 7 million
years ago (see also figure 14.6).
Enter Eugene Dubois.
Dubois was a Dutch physician who was
interested in hominid fossils.
He traveled to Sumatra, largely because
he thought at modern-day orangutans
provided evidence that the “missing link”
might have lived there.
Dubois joined the Dutch
Army as a physician and
was assigned to Sumatra.
After becoming ill, he was
sent to Java. He searched
along the Solo River there,
assisted by convict labor
provided by the Dutch
government.
In 1891, they found a
skullcap. A year later, a
leg bone. He thought he
had found the “missing
link” which came to be
known as “Java Man”.
Most of the scientific
establishment was
skeptical.
Other fossils were
accumulating.
A group of fossils were
discovered near Beijing,
China (then Peking) in the
1920s. They represented
about two dozen
individuals.
Collectively, they gave a
fairly complete
reconstruction of “Peking
Man”, later to be
recognized as Homo
erectus.
Some content that the
African predecessors of
the Asian H. erectus
represent a different
species, Homo ergaster.
Others believe the
similarities between the
two indicate that they
are the same species.
It appears likely that
Homo erectus (or,
perhaps, H. ergaster)
arose in Africa, then
migrated to Asia.
They were tall (some
reaching 6 feet) with
large brains. At this
point, body hair was
likely reduced.
Hunting was central to
their existence.
FIGURE 15.4 Out of Africa
Various species of gracile hominids originated in
Africa and then spread to other continents. This
figure summarizes the approximate times and
geographic locations of hominid species.
The Neandertals
Neandertals seem to have
branched off about 500,000
years ago from the line
leading to modern humans.
They are descended from
Homo heidelbergensis,
which was a contemporary
of H. erectus and also had
an African origin.
H. heidelbergensis spread
northward and briefly
overlapped with the earliest
Neadertals.
Neanderthal Man
Neanderthals were not
ancestors of modern man,
although they did coexist
with modern humans.
Neanderthals arose about
300,000 years ago and
survived until just 30,000
years ago.
Neanderthal man is often
classified as a subspecies
of modern humans, Homo
sapiens neanderthalensis.
Some workers (including
Kardong) prefer to
recognize them as a
separate species, H.
neanderthalensis.
Evidence that some
Neanderthals buried
their dead suggests a
more sophisticated
culture.
And finally, Homo sapiens
The most recent evidence
suggests that species also
has its origins in Africa.
In 1997, Tim White and
coworkers found the
remains of Homo sapiens
approximately 160,000
years old in Ethiopia.
Tim White
By about 100,000 years ago,
Homo sapiens had spread
across Asia.
At this time, they exhibited
tool use and culture very
similar to that of the
Neanderthals.
By about 40,000 years ago,
however, H. sapiens had
surpassed the Neanderthals
in culture. They entered
Europe, and by 30,000 years
ago the Neanderthals were
extinct.
Africa
Homo erectus (white arrows) originated in Africa but spread to parts of Eastern Asia, and
perhaps into Europe. H. neanderthalensis apparently followed much the same migrations
out of Africa as did H. sapiens after them.
FIGURE 15.11 Replacement of
H. erectus by H. sapiens
(a) Multiregional Theory
proposes that after H. erectus
dispersed to various
geographic regions, it
continued to evolve in place,
producing modern humans.
(b) The Out-of-Africa Theory
proposes that after H. erectus
dispersed to various
geographic regions, H.
sapiens arose in Africa, then
also dispersed to other
geographic regions, displacing
H. erectus as it spread.
Current evidence seems to
favor the Out-of-Africa theory.
How did humans reach the New World?
There are several
possibilities. The
most likely is
through Beringia, a
land bridge that
connected Siberia
and Alaska during
the Ice Ages.
FIGURE 15.12
Human Colonization
of the New World
The most likely
routes were through
Beringia via the
coastline or inland
via a land corridor
that opened in the
glacial ice sheets.
Other, although
more speculative,
routes include a
possible Pacific
crossing or an
Atlantic crossing.
(After Campbell and
Loy.)
The arrival of humans
coincided with the
disappearance of many
species of large mammals
from North America.
“Clovis” spearpoints are
found associated with early
human sites across North
America.
It is thought that the
arrival of sophisticated
human hunters led to the
extinction of many
“naïve” species of native
mammals.
Other researchers
have suggested
that the earliest
humans in the
Americas may
have arrived by
sea.
This would help explain archaeological sites in Chile, which seem
too old to have been explained by a Beringia crossing.
DNA results have suggested to some workers an earliest entry
date of 42,000 years ago, long before the Clovis peoples.
The study of skulls has added
to the confusion. Some
prehistoric Americans had
skulls that more closely
resemble southern Asians
than northern ones.
It is possible that humans
reached the Americas
multiple times, by multiple
routes.
FIGURE 15.13 Human Variation
and Relatedness
Based on genetic similarities, the various
ethnic groups of humans can be
compared for their closest human
relationships and nested together
accordingly.