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
(a) New World monkey: spider monkey (b) Old World monkey: macaque
(a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees (e) Bonobos
Most anthropologists believe that humans and apes diverged from a common ancestor 6-8 million years ago
ANCESTRAL PRIMATE Lemurs, lorises, and bush babies Tarsiers New World monkeys Old World monkeys Gibbons Anthropoids Orangutans Gorillas Chimpanzees and bonobos Humans 60 50 40 30 20 10 0 Time (millions of years ago)
(d) Chimpanzees
(e) Bonobos
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
Millions of years ago 0 0.5 Paranthropus boisei Paranthropus robustus Homo ergaster? Homo neanderthalensis Homo sapiens 1.0 1.5 Australopithecus africanus 2.0 2.5 3.0 3.5 4.0 Australopithecus anamensis Kenyanthropus platyops Australopithecus garhi Homo habilis Homo rudolfensis Homo erectus 4.5 5.0 Australopithecus afarensis 5.5 Ardipithecus ramidus 6.0 6.5 7.0 Orrorin tugensis Sahelanthropus tchadensis
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 (a) The Laetoli footprints (b) Artist s reconstruction of A. afarensis
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
Homo habilis 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 ) adult cranial capacity (range in cm 3 ) Chimpanzees 300-500 Australopithecines 400-530 early transitional humans 500-750 modern humans 900-2300
Homo ergaster was the first fully bipedal, largebrained 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 Early Homo
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
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 Homo Sapiens
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.