Chapter 14Human Evolution: The Early Years

Primates have grasping hands, a method of navigation referred to as brachiation.

Primates have nails, not claws or hooves.

Primates have stereoscopic vision, wherein the two eyes scan an overlapping part of the visual field before them. This improves the precision of depth perception.

When a monkey moves from branch to branch; reliable depth perception is crucial, to judge the distance and safely reach the next branch.

Primates have relatively large brains.

primates evolved about 65 million years ago, just as the last of the dinosaurs were flickering out. About 40 million years ago, these early primates split into two surviving groups-the prosimians and anthropoids. The prosimians (basal primates)

large eyes serve them well in their mostly nocturnal lifestyles.

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• Primates are divided into two subgroups.– The Prosimii (prosimians), probably resemble

early arboreal primates and include the lemurs of Madagascar and the lorises, pottos, and tarsiers of tropical Africa and southern Asia.

– The Anthropoidea (anthropoids) include moneys, apes, and humans.

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The anthropoids; platyrrhines -- about 30 million years ago, some early anthropoids made it to South America ( how is still not known).

Another group of anthropoids, the catarrhines, is African in origin.

Table 14.1 Classification of Primates

prehensile tails and

Nostrils open to the side

FIGURE 14.5 Primate Relationships

• Primates divide traditionally into two major groups. The prosimians tend to be small and nocturnal, including bush babies of Africa, the lemurs of Madagascar, and lorises and tarsiers of Southeast Asia. The anthropoids are more derived, including monkeys plus gibbons, apes, and hominids.

• In addition to monkeys, the anthropoid suborder also includes four genera of apes: Hylobates (gibbons), Pongo (orangutans, Gorilla (gorillas), and Pan (chimpanzees and bonobos)--Modern apes are confined exclusively to the tropical regions of the Old World.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 34.37

Fossils, together with molecular structures, pointed to a hominid divergence from chimpanzees at around 7 million years ago.

The Course of Hominid Evolution

These oldest hominids date to between 6 and 7 MYA. Sahelanthropus tchadensis from a nearly complete skull; Orrorin tugenensis consists of pieces of arm, thigh, and jawbones, several teeth

人類從黑星星演變來

Advocates promote one or both of these fossils as common ancestors to chimps and hominids.

The Course of Hominid Evolution

S. tchadensis has a relatively small brain (chimp-like) but brow ridges and small canine teeth (hominid-like). The mixture of features, fits expectations of being close to the common ancestor of Chip. and Hum. from a nearly complete skull; O. tugenensis

人類從黑星星演變來

Ardipithecus ramidus lived almost 4.5 million years ago, in Africa.

Australopithecus anamensis soon followed, 4.2 to 3.9 million years ago.

The robust hominid line,

the gracile hominid line

The Course of Hominid Evolution

Hominid relationships

• Hominids generally evolved in two directions. One, a “robust” line that became extinct about 1 million years ago.

• The other, is the “gracile” line continuing down to modern Homo sapiens.

Long arms; notice that your hands hang at or below your hips.

In primates, the collarbone (clavicle), together with the flat shoulder blade (scapula) on the back, is large to stabilize the shoulder joint and prevent dislocation of the joint during arm swings

Grasping hands; fingers hook a branch; the thumb opposes for a secure grip.

Hominid Features

we walk upright, comfortably on two limbs-a posture and mode of locomotion termed bipedal.

Bipedal posture has its advantages.

With its important sensory receptors-nose (small), ears (hearing), eyes (vision). This provides for better surveillance of opportunities or dangers otherwise

The job shifts to the two hindlimbs exclusively, and the forearms are available for other roles, such as carrying food or infants,

Locomotion

Other features:Large brains; a hair coat; reduced; complex sentence

Ape and hominid skeletons

• Respectively, the backbone joins the back of the skull or bottom. The backbone is arched or S-shaped. The arms are long in both, but shorter than hindlimbs in the ape compared to the hominid. The hips are long or bowl-shaped and the femur (upper leg bone) is angled out or in.

Bipedalism

• Walking comfortably on two hindlegs, bipedalism, evolved early in hominids. Many of the changes in body design and eventually in social systems derive in part from this fundamental change in posture. Some of the major branches in hominid evolution are shown.

Bipedal adaptations I • In hominids, the upright, bipedal posture is derived from primates that are dependent upon a four-footed, quadrupedal posture. Such upright carriage of the body poses special problems in engineering. To accommodate this posture and stabilize it, the hominid gluteus muscles are large (balance leg swing), hips are wide (broad support), the spine curved (centers body weight, shock absorbing), and the position of the spine is beneath the skull (accommodate erect stance). (see also Bipedal adaptations II)

Bipedal adaptations II

• Further adaptations (see also Bipedal adaptations II) to bipedalism include a change of the big toe (hallux) from grasping in apes to striding in hominids, repositioning of the hominid knee more under the pelvis, and shortening of the hips to a broader base of support of the upper body.

Human fossils had been found in Germany (1856) in the Neander Valley, from which they took their common name, Neandertals.

Hominid Evolution—On Becoming Human

half-human and half-ape

From such a beginning, some scientists of the day predicted that upright and bipedal posture would follow.

Although named for Germany's Neander Valley, the first Neanderthal remains were found in Gibraltar.

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Australopithecus africanus

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Taung skull –a child’s storyIn the 1920s, paleontologist Raymond Dart was working not in Europe, but at the southern tip of Africa,

Nearby workmen excavating for lime blasted open a small cave at a location termed Taung.

The teeth were milk teeth –those of a child; “Taung child,” The child had died at about 3 or 4 years of age.

Formally, the fossil was named Australopithecus africanus, roughly translated as “southern ape of Africa.”

A. africanus fossils fall to 2.8 to 2.4 million years ago.

Cleveland Museum of Natural History and currently affiliated with Arizona State University. But in 1973, Johanson was on expedition in eastern Africa in search of early hominid fossils.

Beatles’ song “ Lucy in the Sky with Diamonds” filled the evenings and inspired the common name for this fossil

under 4 million years. She was an adult about 3½ to 4 feet tall, walked bipedally, a female.

Lucy’s bones included the left hip bone. A mirror image of this bone completes the hips, and together the hip bones define the birth canal between them.

FIGURE 14.10 Birth Canal

• Hips of the human male (a) and the human female (b). In humans, the birth of a baby with a relatively large head requires a relatively large birth canal. Note that the inner rims of the hips of a female define a larger birth canal than do those of a male.

In Lucy’s hip, the lever arm for the gluteus maximus muscle was almost twice the length of the lever arm in modern humans.

In 1938, Robert Broom purchased from a collector; Paranthropus robustusIn 1959, Mary Leakey discovered in Africa; Zinjanthropus boisei

Today both fossil finds belong to th same genuks, Australopithecus. Broom’s is A. robustus and Leakey’s is A. boisei

The jaws were heavy and angular; the teeth broad and thick with tough enamel. These were teeth and jaws suited for grinding the coarse fiber of plant tissue.

This robust branch of hominid evolution became extinct about a million years ago, leaving no descendants.

Vegetarians — A Dead End

Australopithecus anamensis, predates Lucy, at about 4.1 million years ago.

Ardipithecus ramidus, from about 4.4 million

The oldest Hominids

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Homo erectus Homo habilis

A. afarensis Australopithecus africanus

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