NOTES: Ch 34 - Mammals & Primate / Human Evolution (34.7-34.8)

Class: MAMMALIA ● Mammals possess unique derived characteristics: 1) Provide young with milk (mammary glands) 2) Internal fertilization; some embryo development within uterus before birth 3) Hair

Class: MAMMALIA ● Mammals possess unique derived characteristics: 4) Endothermic (high metabolic rate) 5) Larger brain (than other vertebrates of similar size) 6) Differentiated teeth

Mammals… ● Most mammals are EUTHERIANS (a.k.a. “placental” mammals”) -highly developed at birth -most are terrestrial, but some are marine -important grazers and browsers in terrestrial ecosystems

● Primates have been present for 65 million years and are defined by shared derived characteristics shaped by natural selection for living in trees: ● limber shoulder joints ● dexterous hands ● sensitive fingers with nails (not claws) ● eyes close together ● excellent hand-eye coordination ● parental care with usually single births and long nurturing ● complex social behavior

New World monkey: spider monkey (b) Old World monkey: macaque Figure 34.44 New World monkeys and Old World monkeys. (a) New World monkey: spider monkey (b) Old World monkey: macaque 6

(a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees (e) Bonobos Figure 34.45 Nonhuman apes. (e) Bonobos 7

● Most anthropologists believe that humans and apes diverged from a common ancestor 6-8 million years ago

Lemurs, lorises, and bush babies ANCESTRAL PRIMATE Tarsiers New World monkeys Old World monkeys Anthropoids Gibbons Orangutans Gorillas Figure 34.43 A phylogenetic tree of primates. Chimpanzees and bonobos Humans 60 50 40 30 20 10 Time (millions of years ago) 9

Figure 34.45 Nonhuman apes. (d) Chimpanzees 10

Figure 34.45 Nonhuman apes. (e) Bonobos 11

Derived Characters of Humans ● A number of characters distinguish humans from other apes -Upright posture and bipedal locomotion -Larger brains capable of language, symbolic thought, artistic expression, the manufacture and use of complex tools -Reduced jawbones and jaw muscles -Shorter digestive tract

The Earliest Hominins ● The study of human origins is known as paleoanthropology ● Hominins are more closely related to humans than to chimpanzees ● Paleoanthropologists have discovered fossils of about 20 species of extinct hominins

Paranthropus robustus Homo ergaster Homo neanderthalensis Homo sapiens ? Paranthropus boisei 0.5 1.0 1.5 Australopithecus africanus 2.0 Kenyanthropus platyops 2.5 Australopithecus garhi Australo- pithecus anamensis Millions of years ago 3.0 Homo erectus 3.5 Homo rudolfensis Homo habilis 4.0 4.5 Figure 34.46 A timeline for some selected hominin species. Australopithecus afarensis 5.0 Ardipithecus ramidus 5.5 6.0 Orrorin tugensis 6.5 Sahelanthropus tchadensis 7.0 14

● Misconception: Early hominins were chimpanzees **Correction: Hominins and chimpanzees shared a common ancestor ● Misconception: Human evolution is like a ladder leading directly to Homo sapiens **Correction: Hominin evolution included many branches or coexisting species, though only humans survive today

The First Humans: Australopiths ● Australopiths are a paraphyletic assemblage of hominins living between 4 and 2 million years ago ● Some species, such as Australopithecus afarensis walked fully upright

The First Humans: Australopiths Figure 34.48 Evidence that hominins walked upright 3.5 million years ago. (a) The Laetoli footprints (b) Artist’s reconstruction of A. afarensis 18

Chimpanzee Australopithecus africanus Homo sapiens The First Humans: ● Australopithecus africanus: walked upright; humanlike teeth and hands brain was about 1/3 size of modern humans 4 million years ago; existed for 3 million yrs. Chimpanzee Australopithecus africanus Homo sapiens

● Australopithecus afarensis (“Lucy”) upright posture evidence of coexistence with A. africanus for about 1 million years

● Australopithecus anamensis: about 4 m.y.a. ● Ardipithecus ramidus: about 4.4 m.y.a.

● hominids walked upright for two million years without a substantial increase in brain size! ● this posture may have freed the hands for other things such as gathering food or caring for infants

Early Homo ● The earliest fossils placed in our genus Homo are those of Homo habilis, ranging in age from about 2.4 to 1.6 million years ● Stone tools have been found with H. habilis, giving this species its name, which means “handy man”

adult cranial capacity (range in cm3) Homo habilis adult cranial capacity (range in cm3) Chimpanzees 300-500 Australopithecines 400-530 early transitional humans 500-750 modern humans 900-2300 ● enlargement of brain is evident in fossils dating back to about 2.4 -1.6 m.y.a. (650 cc vs. 500 cc) ● simple stone tools found with larger-brained fossils ● coexisted with A. africanus for almost 1 million years  (A. africanus was an evolutionary “dead end”)

Early Homo ● Homo ergaster was the first fully bipedal, large-brained hominid ● The species existed between 1.9 and 1.5 million years ago ● Homo ergaster shows a significant decrease in sexual dimorphism (a size difference between sexes) compared with its ancestors

Homo erectus & descendants ● taller and larger brain than H. habilis (1200 cc) ● first hominid to migrate out of Africa ● 1.8 m.y.a. to 250,000 years ago

● H. erectus remains have been found on other continents ● diet shifted to include a larger portion of meat ● intelligence allowed them to survive in colder climates (lived in huts or caves, built fire, wore clothing, designed more refined tools)

**best known descendants of H. erectus are Neanderthals! -lived in Europe, Middle East, & Asia -they were thick-boned with a larger brain, they buried their dead, and they made hunting tools -350,000 to 28,000 years ago

The Origin of Modern Humans (2 theories): 1) Multiregional Model 2) Monogenesis Model (“Out of Africa” model)

1) Multiregional Model ● proposes that modern humans evolved in parallel along the same lines in different parts of the world *if true, then… ● the geographic diversity of humans originated between 1-2 m.y.a. when H. erectus first spread from Africa to other continents

2) Monogenesis Model (“Out of Africa” model) ● proposes that modern humans evolved from the H. erectus group(s) that stayed in Africa; they then dispersed from Africa, displacing the Neanderthals and other hominids (suggests the Neanderthals were NOT ancestors of modern humans since they coexisted and were probably evolutionary dead ends) *if true, then… ● the geographic diversity of humans developed within the last 100,000 years

● Mitochondrial DNA (mtDNA) studies support the monogenesis model.                                                     

Homo Sapiens ● Homo sapiens appeared in Africa by 195,000 years ago ● All living humans are descended from these African ancestors

Homo Sapiens Figure 34.51 A 160,000-year-old fossil of Homo sapiens. 42

Homo Sapiens ● The oldest fossils of Homo sapiens outside Africa date back about 115,000 years and are from the Middle East ● Humans first arrived in the New World sometime before 15,000 years ago ● Homo sapiens were the first group to show evidence of symbolic and sophisticated thought

Cultural Evolution: ● the basis of culture is learning from the experiences of earlier generations ● transmission of information is by written and spoken language

Cultural Evolution & Learning *Cultural learning facilitated spread of domesticated plants and animals  Human societies converted from hunters & gatherers to PASTORAL (herding large animals) and AGRICULTURAL

Human Population Growth: Three phases: 1) Tool use: lasted about 1 million years -POP. = 5 million ppl. 2) Domestication of plants & animals: lasted about 8,000 years -POP. = 500 million ppl.

Human Population Growth: 3) Industrial Revolution: started about 300 years ago -CURRENT POP. = 7.0 billion ppl. -EST. POP. by 2050 = 11 billion ppl.