21.1. Humans Are Primates (p. 348)
A. Human Evolution
1. Evolution of human beings can be traced back to the Cambrian period when all animals originated. (Fig. 21.1) [transp. 122]
2. Fishes dominated the seas and insects were among the first to live on land and they are most diverse.
3. Among vertebrates, amphibians first dominated the terrestrial environment but reptiles soon took over.
4. Mammals evolved from mammal-like reptiles by the Triassic period.
a. Mammals are members of a class of vertebrates characterized by presence of hair and mammary glands.
b. Mammals remained small and insignificant while the dinosaurs dominated the land for over 150 million years.
c. Extinction of dinosaurs at end of Mesozoic era permitted diversification of mammals during Cenozoic era.
B. What Are Primate Characteristics?
1. Primate hands have an opposable thumb; this characteristic allowed primates to easily harvest food.
2. Primates have a reduced snout, and eyes are moved to the front of the face (stereoscopic vision).
3. Primates have more single births, which reduces need for care for several offspring and allows forebrain development.
4. Period of parental care is extended with an emphasis on learned behavior and complex social interactions.
21.2. Primates Are Diverse (p. 349)
A. The primate order contains two suborders: prosimians and anthropoids.
B. Prosimians Came First (Fig. 21.2)
1. Prosimians diverged first and are most closely related to the original primate.
2. Prosimians belong to the suborder Prosimii and includes the lemurs, tarsiers, and lorises.
a. Tarsiers are small, Nocturnal, mouse-sized insectivores found in Philippines and East Indies. (Fig. 21.2b)
b. Lemurs are squirrel-like fruit eaters confined largely to the island of Madagascar. (Fig. 21.2c)
c. Lorises are prosimians living in Africa and Asia and resemble lemurs.
d. Evolution of prosimians followed spread of forests. (Fig. 21.3) [transp. 123]
C. Anthropoids Followed
1. Anthropoids belong to the suborder Anthropoidea, which includes three superfamilies:
a. New World monkeys (Ceboidea) reside in South America and diverged first. (Fig. 21.3) [transp. 123]
1) Therefore, New World monkeys are less closely related to Old World monkeys than they are to apes.
2) New World monkeys (e.g., spider monkey and capuchin) have long prehensile tails and flat noses.
b. Old World Monkeys (Cercopithecoidea) took up residence in Africa and Asia.
1) Old World monkeys (e.g., baboon and rhesus monkey) lack prehensile tails and have protruding noses.
c. Hominoids include all the apes and the humans. (Fig. 21.4)
1) Proconsul was prevalent in Africa during the Miocene and is believed ancestral to apes and humans.
2) At the end of the Miocene epoch, Africa joined with Asia, and the hominoids migrated into Europe.
3) The two ancestral groups included dryomorphs and ramamorphs (that were ancestral to orangutans).
D. Learning from Living Hominoids
1. Humans and apes are closely related and placed in the same superfamily, Hominoidea.
2. Four types of apes exist: gibbons and orangutans (Asia) and gorillas and chimpanzees (Africa). (Fig. 21.5)
3. Using amino acid and DNA base-pairs as a molecular clock, humans are most closely related to African apes.
a. Monkey ancestors diverged from the primate line about 33 million years ago.
b. The orangutan line diverged about 10 million years ago.
c. The ancestors of African apes and hominids diverged about 6 million years ago.
4. Hominoid evolution continued in eastern Africa, separate from the evolution of apes in the rest of the continent.
a. Hominoids include the australopithecines; extinct and modern humans.
b. The Rift Valley separated eastern Africa from the rest of Africa while volcanos and lakes formed a barrier.
c. The environment slowly changed from forests to savannas.
d. Type of locomotion changed, which is dependent on the spine, the pelvis, and the bones of the appendages.
e. In a grassland, it was adaptive to stand tall to look over grasses if searching for food or avoiding predators.
f. Also, an erect posture left the hands free to throw rocks and even manipulate tools as the brain grew larger.
g. The shape of the jaw is related to the size and the shape of the teeth, and was adaptive to a new diet.
21.3. Hominoids Break Away (p. 354) (Fig. 21.7-9) [transp. 124]
A. Australopithecines belong to the genus Australopithecus, and contain the first generally recognized hominids.
B. Australopithecus ramidus is based on bone fragments dated at 4.4 MYA; represents a transitional stage between apes and humans; compared to later australopithecines, its cheek teeth were smaller, canine teeth larger, and skull more like that of a chimpanzee.
C. Australopithecus afarensis is based on many skeletal fragments (Lucy) dated at 3.18 MYA.
1. This australopithecine had an apelike face with prominent brow ridges, a projecting jaw and dentition of an ape (Fig. 21.8), but is thought to have stood upright and walked bipedally. (Fig. 21.7).
2. Australopithecines display mosaic evolution, more apelike from the waist up and humanlike below the waist.
3. They are sexually dimorphic: females are 4 feet tall and about 30 kg, males are 5 feet tall and up to 45 kg.
4. Finds in 1994 confirmed the many fossils were one species and dated to about 3 million years ago.
5. Australopithecines may have had lives similar to modern baboons, traveling and foraging in troops.
D. After a period during which only A. afarensis existed, speciation may have resulted in 10 species.
1. Descendants of A. afarensis had a brain size of about 500 cc, probably ate meat and may have made tools.
2. Australopithecus africanus described by Raymond Dart in the 1920s is a gracile type from southern Africa.
3. Australopithecus boisei is a robust form from eastern Africa; it had stronger jaws, larger attachments for larger chewing muscles, and bigger grinding teeth because it probably fed on tougher foods than the gracile forms; lived in drier habitats where soft fruits and leaves would be harder to obtain, and probably ate meat.
4. Australopithecus robustus was similar to A. boisei; with jaws, teeth and habitat similar to A. boisei.
5. Australopithecus aethiopicus, discovered by Alan Walker, is ancestral to robust forms of australopithocines.
E. Homo habilis Made Tools
1. The oldest fossils to be classified in the genus Homo are known as Homo habilis.
2. H. habilis warrants classification as a Homo because of brain size related to speech, posture, and dentition.
3. Cut marks on bones suggest the use of tools to prepare meat and possible scavenging.
4. Oldowan tools associated with H. habilis includes flakes used to scrape away hide or remove meat.
5. A large brain (700 cc) indicates that this hominid may have had speech to help in cooperation and sharing.
6. Culture involves both behavior and products dependent upon capacity to learn and transmit knowledge.
7. Possession of culture by H. habilis may have hastened extinction of the australopithecines.
F. Homo erectus Traveled
1. Homo erectus fossils were found in Africa, Asia and Europe and date between 1.9 and 0.5 million years ago.
2. Eugene DuBois was a Dutch anatomist who unearthed the first H. erectus bones in Java in 1891.
3. H. erectus had a brain capacity of 1,000 cc, was taller than H. habilis, and had a striding gait. (Fig. 21.10)
4. H. erectus first appeared in Africa and then migrated to Asia and Europe.
5. This was the first hominid to use fire, to be a systematic game hunter, and possibly, to use home bases.
G. Modern Humans Originated How?
1. Two contradicting hypotheses have been suggested about the origin of modern humans. (Fig. 21.11) [transp. 125]
2. The multiregional continuity hypothesis proposes that modern humans originated separately in Asia, Europe, and Africa; if valid, then a distinctive continuity in anatomy and genetic variation is expected in each location.
3. The out-of-Africa hypothesis states that modern humans originated only in Africa and after migrating into Europe and Asia, they replaced the archaic Homo species found there.
a. All extant humans are descended from a few individuals from about 100,000 years ago.
b. Mitochondrial DNA analyses indicate a close genetic relationship among all Europeans; although the first analysis was flawed, the data tend to support the out-of-Africa hypothesis.
H. Neanderthals Were Archaic
1. Neanderthals were named for Neander Valley where skeletons were found and dated to 200,000 years ago.
2. Neanderthals are classified as H. sapiens neanderthalensis.
3. Classic Neanderthal anatomy includes massive brow ridges; a nose, jaws, and teeth that protruded forward; a low sloping forehead; a lower jaw sloping back without a chin; a longer pubic bone; a slightly larger brain than that of modern humans; shorter and thicker limb bones; and heavier muscles in shoulder and neck.
4. It is speculated that a larger brain than that of modern humans was required to control the extra musculature.
5. Sturdy build of Neanderthals was likely adaptation to cold climate; they lived in Eurasia during last Ice Age.
6. The Neanderthals give evidence of being culturally advanced.
a. Most lived in caves, but those who lived in the open may have built houses.
b. They manufactured a variety of stone tools, including spear points, scrapers, and knives.
c. They used and could control fire, which probably helped in cooking frozen meat and in keeping warm.
d. They buried their dead with flowers and tools and may have had a religion.
I. Cro-Magnons Were Modern Humans
1. Cro-Magnons are modern humans (H. sapiens sapiens) thought to have entered Eurasia 100,000 years ago.
2. Cro-Magnons are named for a fossil location in France and had a thoroughly modern appearance. (Fig. 21.13)
3. They had advanced Aurignacian stone tools and may have been the first to throw spears.
4. Cro-Magnons hunted cooperatively, and perhaps were the first to have had a language.
5. Cro-Magnons may have been responsible for extinction of large mammals during the late Pleistocene.
6. Cro-Magnon culture included figurines carved out of bone and antler, and cave paintings. (Fig. 21.13)