Australopithecus

The scientists who discovered Au. sediba suggest this species is a transitional form be-tween Au. africanus and the genus Homo. This has been criticized by other scien-

tists who point out that the earliest dates for the genus Homo are around 2.4 ma (Homo rudolfensis. This predates Au. sediba by about 500,000 years, making

it impossible all populations of early Homo descended from Au. sediba.. Additionally, some African H. erectus are dated to around 1.8 ma, only

about 100 ka younger than Au. sediba, with features so derived that it is very unlikely that this species gave rise to them. These sci-

entists suggest Au. sediba represents the termination of the Au. africanus line in South Africa and did not contribute

to the genus Homo. Because of the mix of primitive and derived features present in Au. sediba, scien-

tists debate whether it should be attributed to the genus Homo or to the genus Australo-

pithecus. Some scientists argue that be-cause Au. sediba shares traits with

members of the genus Homo not found in any australo-

piths species, it should be assigned to Homo.

Others,however, ar-guerather than

by individu traits, a

gen.

Many of the features that distinguish Homo erectus from other hominin species—both earlier and later species—are seen in the skull. The aver-age brain size of Homo erectus is estimated to have been roughly 900 cubic centimeters (cc.), which is larger than Homo habilis, but smaller than that of Homo heidelbergensis and other later forms. The size of the Homo erectus brain is negligibly larger than in Homo habilis when it is con-sidered as in relation to body size—i.e., brain size increased substantially in Homo erectus, but, because body size also increased, the relative size of the Homo erectus brain is not considerably larger than that of Homo habilis. The absolute in brain size, however, caused changes in the brain case; for instance, the braincase is higher than in Homo habilis, but lower than in later hominin species. The Homo erectus braincase is also very long relative to its height, giving the skull a football-shape when viewed from the side. The braincase and the face and jaws of Homo erectus were very heavily built, with thick bones and extreme thickenings along some of the skull sutures (where two skull bones connect). For instance, the browridges were massively built and continuous across the face and large, bony prominences existed in the back of the skull (the occipital torus and angular torus). Due to these prominences, the cranium of Homo erectus is pentagon-shaped when viewed from behind, with the widest area co-inciding with the bottom of the cranium.In addition to their use to define the species, cranial remains have also been used to study the way that Homo erectus grew and developed into adulthood. Despite extensive study, scholars disagree about how the evidence bearing on this subject should be interpreted. Evidence from the teeth of Homo erectus fossils suggests that Homo erectus had not yet evolved the unique growth schedule exhib-

Homoerectus

Some of the earliest H. heidelbergensis fos-sils, dating roughly between 600 and 400 kya

(thousand years ago), are found in Africa. Kabwe, one of the most famous H. heidelbergensis speci-

mens, was found at a mining site in 1921 and cannot be accurately dated, but most researchers agree that it is

Middle Pleistocene in age (at least 125 ky old and possibly earlier). Other sites in Africa, including Bodo (dated to about 600

kya), contain stone tools resembling the Acheulean tools used by H. erectus. However, the tools used by H. heidelbergensis were thinner and

more finely flaked than those used by H. erectus, leading researchers to hypothesize the change in tool manufacture reflects a behavioral change that

can be linked to a speciation event (an evolutionary process by which new species arise) in which H. erectus gave rise to a new species with a larger brain and possess-ing the capability of engaging in more complex behaviors. Along with stone tools,

the remains of hippos, baboons, and antelopes with cut marks (marks made by stone tools) on the bone are often found at Middle Pleistocene sites in Africa,

suggesting that H. heidelbergensis was butchering meat. Cut marks on the face around the eye sockets of the Bodo cranium have suggested

it also was butchered.Much of the information we have about H. heidelbergensis comes from sites in Europe. Some fossil skulls

from the Middle Pleistocene in Europe very closely resemble those found in Africa. Examples are a skull from Petralo-

na, Greece (whose exact date is unknown but is likely Middle Pleistocene in age), and a partially distort-

ed facial skeleton from Arago in France (dating

Heidelbergensis

NeanderthalisSome of

the earliest H. heidelbergensis fos-sils, dating roughly between 600 and 400 kya

(thousand years ago), are found in Africa. Kabwe, one of the most famous H. heidelbergensis specimens, was found

at a mining site in 1921 and cannot be accurately dated, but most researchers agree that it is Middle Pleistocene in age (at least 125 ky old

and possibly earlier). Other sites in Africa, including Bodo (dated to about 600 kya), contain stone tools resembling the Acheulean tools used by H.

erectus. However, the tools used by H. heidelbergensis were thinner and more finely flaked than those used by H. erectus, leading researchers to hypothesize the

change in tool manufacture reflects a behavioral change that can be linked to a spe-ciation event (an evolutionary process by which new species arise) in which H. erectus

gave rise to a new species with a larger brain and possessing the capability of engaging in more complex behaviors. Along with stone tools, the remains of hippos, baboons, and an-telopes with cut marks (marks made by stone tools) on the bone are often found at Middle Pleistocene sites in Africa, suggesting that H. heidelbergensis was butchering meat. Cut marks on the face around the eye sockets of the Bodo cranium have suggested it also was butchered.Much of the information we have about H. heidelbergensis comes from sites in Europe. Some fossil skulls from the Middle Pleistocene in Europe very closely resemble those found in Africa. Examples are a skull from Petralo-na, Greece (whose exact date is unknown but is likely Middle Pleistocene in age), and a partially distorted facial skeleton from Arago in France (dating roughly to 450 kya). Some scientists recognize features in European

H. heidelbergensis that seem to foreshadow features distinctive of Homo neanderthalensis. For example, the face of the

Arago fossil, according to some researchers, has a flattened cheek where the zygomatic

arches (cheek-

Homo SapiensThe la-

test chapter of human evo-lution begins with the emergence of

Homo sapiens. The anatomy of Homo sapiens is unique among hominin species and appears first in

East Africa, dating to roughly 160 thousand years ago (ka). These unique features—including changes in the skull and post-

cranial skeleton (skeleton minus skull)—suggest changes in brain size and architecture and an adaptation to tropical environments. These

anatomical changes are linked to cognitive and behavioral changes that are equally unique among hominin species. In particular, the archaeological

evidence of behaviors thought to be unique to Homo sapiens, which appear first in Africa around 170 ka, highlight the importance of symbolism, complex cog-nitive behaviors, and a broad subsistence strategy (the strategy used to procure food). The evolution of Homo sapiens is vitally important to defining our species in the broader context of human evolution and also has key to understanding the human condition, past and present.Many of the unique features of Homo sapiens are found in the skull. Brain size estimates suggest that the brain of Homo sapiens was larger than in other hominin species. The average crani-al capacity of Homo sapiens is roughly 1300 cubic centimeters, making

the brains of this species absolutely smaller than those of Homo ne-anderthalensis. However, due to its gracile (small and lightly built)

postcranial skeleton (see below), the brain of H. sapiens was larger relative to body size than that of H. neanderthalen-

sis. The skull itself is much taller than earlier hom-inin species and the skull is therefore much

shorter (from front to back) in relation to