Encyclopedia of Evolution.pdf - Online Reading Center

Homo heidelbergensis
H. habilis was the first species to deliberately fashion stone
tools. The simple Oldowan tools (see photo below) do not
look much different from natural rocks, but microscopic
analysis shows bulbs of percussion where the tools were
deliberately struck to form sharp surfaces.
The fact that the oldest Oldowan tools predate the earliest
H. habilis fossils brings up the possibility that the tools
were made by other hominins, such as the Paranthropus
robust australopithecines. However, even though the hands of
Paranthropus were probably capable of making stone tools,
Paranthropus did not make stone tools in other parts of its
range, or later in its history. The best explanation is that Oldowan
tools were more likely to be preserved than H. habilis
fossils, and that scientists have simply not yet found fossils
from the earliest H. habilis populations.
The increase in brain size, the consumption of meat,
and the use of stone tools may all have depended upon one
another. Larger brains allowed H. habilis to locate carcasses
by watching vultures and by learning the habits of leopards,
which stash their prey in trees. The meat and marrow provided
fats and calories that were important to the growth
of the brain, which is a physiologically expensive organ.
Larger brains allowed the ability to design and produce stone
tools, and the tools unlocked new sources of calories for the
brain. Once brain size had begun to increase, natural selection
favored the ability to find and process carcasses, which
in turn created a selective advantage for yet larger brains.
The evolutionary increase in brain size may therefore have
resulted from a positive feedback process.
Most of the increase in the size of the H. habilis brain
over that of australopithecine ancestors, and the design of
stone tools, occurred early in the evolutionary history of H.
habilis. After an initial burst of brain growth and creativity
in tool production, H. habilis may have experienced a million
year anatomical and cultural stasis (see punctuated equilibria).
According to paleontologists such as Steven Stanley,
the initial burst of evolution that produced H. habilis may
have resulted from rapid climate change that made much of
These Oldowan stone tools, found in East Africa, represent the earliest
stone tool technology in the human genus. (Courtesy of Katherine Schick
and Nicholas Toth, Indiana University)
Africa cooler and drier, with the resulting spread of savannas
at the expense of forests, about two and a half million years
ago. The next stage of human evolution, which produced
species such as H. ergaster, occurred when another climate
change spread across Africa, resulting in yet more extensive
savannas.
Further Reading
Johanson, Donald, and James Shreeve. Lucy’s Child: The Discovery
of a Human Ancestor. New York: William Morrow, 1989.
Leakey, Richard, and Roger Lewin. Origins Reconsidered: In Search
of What Makes Us Human. New York: Doubleday, 1992.
Stanley, Steven M. Children of the Ice Age: How a Global Catastrophe
Allowed Humans to Evolve. New York: Harmony Books,
1996.
Tattersall, Ian, and Jeffrey Schwartz. Extinct Humans. New York:
Westview Press, 2000.
Homo heidelbergensis This species of humans, named
after the Heidelberg man fossils found in Germany in 1907,
is intermediate between Homo ergaster (the African
“erectus”) and the two large-brained human species. H.
heidelbergensis evolved in Africa from H. ergaster ancestors,
principally by an increase in brain size from about 56
to about 75 cubic inches (900 to 1,200 cc). Numerous specimens
of this species have been found (see table).
Some H. heidelbergensis populations migrated to Europe.
H. heidelbergensis may not have been the first human species
to migrate from Africa to Europe. Acheulean stone flakes
found at ’Ubeidiya near the Jordan River are between 1.0 million
and 1.4 million years old and may represent northward
and eastward migrations of H. ergaster. The human remains
found at Gran Dolina (the “large depression”), one of the limestone
caves of the Sierra de Atapuerca of Spain, may have been
descendants of an early, failed migration of H. ergaster into
Europe. Anthropologist Juan Luis Arsuaga recognizes these
populations as a separate species, H. antecessor (“explorer”).
These specimens represent at least six humans, and numerous
other animals, that died about 780,000 years ago. About a
quarter of the human bones have chop and cut marks, which
suggests cannibalism. (See the table for examples of possible
intermediates between H. ergaster and H. heidelbergensis.)
H. heidelbergensis persisted in Europe until about a quarter
million years ago, by which time some of them had evolved
into the earliest H. neanderthalensis (see Neandertals) and the
rest had become extinct. Skeletal remains of individuals intermediate
between H. heidelbergensis and Neandertals have been
found in Europe, such as at Petralona in Greece (see missing
links) and the Sima de los Huesos (the bone pit) in the Sierra
de Atapuerca of Spain. At 400,000 years of age, the Sima de los
Huesos remains strongly resemble H. heidelbergensis, particularly
in brain size, but have some Neandertal characteristics as
well: in particular, a projecting face and an oval of porous bone
on the rear of the skull. Although the age distribution of these
28 or more individuals is not what would be expected from
normal death, they show no evidence of violence or cannibalism.
All of the bones are broken, but some researchers believe
that whole bodies were originally thrown in and therefore