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Chapter 23 Lecture Outline See separate PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright © 2016 McGraw-Hill Education. Permission required for reproduction or display. 1 Human Evolution 2 Points to ponder • What is chemical evolution? • What is biological evolution? • What is natural selection, and what three elements are vital for this? • What was Darwin’s contribution to evolution? • What have we learned from the fossil record? • Explain the fossil, biogeographical, anatomical, and biochemical evidence that supports the theory of evolution by common descent. • What are analogous, homologous, and vestigial structures? Give examples of each. 3 Points to ponder • How are humans classified? • What characteristics do primates have in common? • Explain the evolution of hominids. • Who was Lucy? • Explain the evolution of humans. • What is the most widely accepted hypothesis for the evolution of modern humans? • Compare and contrast Cro-Magnons and Neandertals. 4 23.1 Origin of Life Origin of life through chemical evolution • Steps of chemical evolution – Gases of the primitive atmosphere formed small organic molecules. – Molecules combined to form macromolecules. – Only RNA might have been needed to form the first cells; this is supported by the fact that RNA can act as enzymes called ribozymes (RNA-first hypothesis). 5 23.1 Origin of Life Origin of life through chemical evolution – Protocells made of proteins and lipids could metabolize by using oceanic organic molecules, but could not reproduce. – The true cell can reproduce and has DNA as its genetic material. 6 23.1 Origin of Life Origin of life through chemical evolution Biological Evolution Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cell Stage 4 DNA RNA origin of genetic code protocell Stage 3 plasma membrane polymers Stage 2 Chemical Evolution polymerisation small organic molecules energy capture Stage 1 abiotic synthesis inorganic chemicals early Earth Figure 23.1 Chemical and biological evolution. 7 23.2 Biological Evolution Biological evolution • Biological evolution – change in population or species over time • Two important points 1. Living things descended from a common ancestor and thus have common chemistry. 2. Livings things adapt to their environment. • Adaptation – a characteristic that enables an organism to survive and reproduce in its environment 8 23.2 Biological Evolution Natural selection • Natural selection is a theory by Charles Darwin that describes a mechanism by which a species becomes adapted to its environment. 9 23.2 Biological Evolution Natural selection • Three vital elements • Variation – there must be physical variations that can be passed from generation to generation • Competition – there must be competition for limited resources (food, mates, shelter), and those better adapted will survive and reproduce • Adaptation – subsequent generations will see an increase in individuals with the same adaptations, as long as the environment remains unchanged 10 23.2 Biological Evolution Natural selection Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lamarck’s proposal Figure 23.3 The two major mechanisms for evolutionary change in the nineteenth century. Darwin’s proposal Originally, giraffes had short necks. Originally, giraffe neck length varied. Giraffes stretched their necks in order to reach food. Competition for resources causes long-necked giraffes to have the most offspring. With continual stretching, most giraffes now have long necks. Due to natural selection, most giraffes now have long necks. 11 23.2 Biological Evolution Evidence to support the theory of evolution by common descent 1. 2. 3. 4. Fossil record Biogeographical evidence Anatomical evidence Biochemical evidence 12 23.2 Biological Evolution 1. What are fossils? • Fossils are the traces of past life. • Fossils allow us to trace the descent of a particular group. • Charles Darwin, an English naturalist, relied on fossils to formulate the theory of evolution. • Transitional fossils have characteristics of two different groups. 13 23.2 Biological Evolution Transitional fossils Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Amphibian tetrapod 360 Early amphibian Millions of years ago (MYA) Expanded ribs Flat head, eyes on top Neck 370 Scales Tiktaalik roseae Fins 377 380 Figure 23.4 Transitional fossils. Rounded head, eyes on sides Fish 14 23.2 Biological Evolution What have we learned from the fossil record? • The fossil record tells us that life progressed from simple to more complex. • Prokaryotes are the first life forms seen in the fossil record, followed by unicellular eukaryotes, and then multicellular eukaryotes. • Fishes evolved before terrestrial plants and animals. • Nonflowering plants preceded flowering plants. • Amphibians preceded reptiles. • Dinosaurs are directly linked to birds. 15 23.2 Biological Evolution Fossils Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. wing wing head tail a. Ambulocetus 50 MYA b. Basilosaurus 40 MYA feathers feet Archaeopteryx fossil teeth tail with vertebrae claws artist depiction of Archaeopteryx (fossil, left): © Jean-Claude Carton/PhotoShot; (drawing, right): © Joe Tucciarone modern c. Right whale a (fossil Ambulocetus foot): © J.G.M. Thewissen, Northeastern Ohio Universities College of Medicine Figure 23.5 Archaeopteryx. Figure 23.6 Evolution of the whales. 16 23.2 Biological Evolution 2. Biogeographical evidence • • • • Biogeography is the study of the distribution of plants and animals throughout the world. It supports the hypothesis that organisms originate in one locale and then may spread out. Different life forms are expected whenever geography separates them. Islands have many unique life forms because of geographic isolation. 17 23.2 Biological Evolution Biogeographical evidence Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sugar glider, Petaurus breviceps, is a tree-dweller and resembles the placental flying squirrel. The Australian wombat, Vombatus, is nocturnal and lives in burrows. It resembles the placental woodchuck. Figure 23.7 Biogeography. Kangaroo, Macropus, is an herbivore that inhabits plains and forests. It resembles the placental Patagonian cavy of South America. (sugar glider): © ANT Photo Library/Photo Researchers; (wombat): © Photodisc Blue/Getty RF; (kangaroo): © George Holton/Photo Researchers 18 23.2 Biological Evolution 3. Anatomical evidence • Common descent hypothesis offers plausible explanation for anatomical similarities among living organisms. • Homologous structures – structures anatomically similar that are inherited by a common ancestor • e.g., Vertebrate forelimbs 19 23.2 Biological Evolution 3. Anatomical evidence • Analogous structures – structures that serve the same function but they do not share a common ancestry, and thus are not constructed the same • e.g., Wings of a bird and wings of an insect • Vestigial structures – anatomical features fully developed in one group that are reduced and may have no function in another group • e.g., Whales have a vestigial pelvic girdle and legs 20 23.2 Biological Evolution An example of homologous structures Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. bird humerous ulna radius metacarpals phalanges bat whale Figure 23.8 Vertebrate forelimbs are homologous structures. cat horse human 21 23.2 Biological Evolution Homologous structures in vertebrate embryos Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pig embryo pharyngeal pouches Figure 23.9 Homologous structures in vertebrate embryos. postanal tail Chick embryo (both): © Carolina Biological Supply/Phototake 22 23.2 Biological Evolution 4. Biochemical evidence • Almost all living things use the same biochemicals (e.g., DNA and ATP). • Living things use the same triplet genetic code. • Living things use the same 20 amino acids in their proteins. • Living things share many of the same genes. 23 23.2 Biological Evolution Biochemical evidence describes evolutionary relationships Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Species Number of Amino Acid Differences Compared to Human Cytochrome c 0 human Cytochrome c is a small protein that plays an important role in the electron transport chain within mitochondria of all cells. 2 monkey 9 pig 11 duck 18 turtle 20 fish Figure 23.10 Biochemical evidence describes evolutionary relationships. 30 moth 51 yeast 24 22.3 Classification of Humans The evolution of humans 25 23.3 Classification of Humans 3 domains of life Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. fungi plants animals EUKARYA protists heterotrophic bacteria protists cyanobacteria ARCHAEA BACTERIA Figure 23.11 The three domains of life. common ancestor 26 23.3 Classification of Humans Primates • Characteristics • • • • Opposable thumb Stereoscopic vision (depth perception) Well-developed brain Reduced number of offspring (usually a single birth) with an increased period of parental care • Emphasis on learned behavior and social interactions 27 23.3 Classification of Humans Primates • Two major groups (suborders) • Prosimians – includes lemurs, tarsiers, and lorises • Anthropoids – includes monkeys, apes, and humans 28 23.3 Classification of Humans Asian and African apes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Asian Apes African Apes western lowland gorilla, Gorilla gorilla white-handed gibbon, Hylobates lar orangutan, Pongo pygmaeus chimpanzee, Pan troglodytes (gibbon): © Hans & Judy Beste/ Animals Animals; (orangutan, chimps, gorillas): © Creatas/PunchStock RF Figure 23.12 Asian and African apes. 29 23.3 Classification of Humans Comparing the human skeleton to the chimpanzee Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Human spine exits from the skull’s center; ape spine exits from rear of skull. Human spine is S-shaped; ape spine has a slight curve. Human pelvis is bowl-shaped; ape pelvis is longer and more narrow. Human femurs angle inward to the knees; ape femurs angle out a bit. Human knee can support more weight than ape knee. Human foot has an arch; ape foot has no arch. a. b. Figure 23.13 Adaptations in the human skeleton allow upright locomotion. 30 23.4 Evolution of Hominins Evolution of primates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Humans Hominines Hominids Hominoids Prosimians Anthropoids hominin Chimpanzees common chimpanzee Gorillas western lowland gorilla Orangutans Bornean orangutan Gibbons white-handed gibbon rhesus monkey Old World Monkeys Mammalian ancestor enters trees. capuchin monkey Tarsiers Philippine tarsier ring-tailed lemur Lemurs 70 Figure 23.14 The evolutionary tree of the primates. 60 50 40 30 Million years Ago 20 (MYA) 10 Prosimians Anthropoids New World Monkeys PRESENT 31 23.4 Evolution of Hominins Evolution of hominins • Hominins – All species of the genus Homo and their close relatives • Characteristics • Bipedal • Flatter face with more pronounced chin • Brain size 32 23.4 Evolution of Hominins Evolution of hominins • Suggested fossils of the first hominins (6-7 MYA) • Central African fossil 7 MYA (Sahelanthropus tchadensis) • Eastern African fossil 6 MYA (Orrorin tugenensis) • Eastern African fossil 5.8-5.2 MYA (Ardipithecus kadabba) • Hominins split from the ape line of descent 7 MYA. 33 23.4 Evolution of Hominins Australopithecines • A group of hominins that evolved and diversified in Africa ~3 MYA. • Some had slight frames and others were robust with massive jaws for feeding on plant materials. • They walked upright. • Limbs proportions are apelike. • They had a small brain. 34 23.4 Evolution of Hominins Australopithecines • Famous skeleton named “Lucy” is from this group . • Australopithecus africanus, with a large brain, is the most likely ancestral candidate for early Homo. 35 23.4 Evolution of Hominins Australopithecines Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. a: © Dan Dreyfus and Associates; b: © John Reader/Photo Researchers Figure 23.15 Australopithecus afarensis. 36 23.5 Evolution of Humans Characteristics of Homo 1. Brain size is 600 cc or greater. 2. There is evidence of tool use. 3. Jaw and teeth of Homo resemble humans. Early Homo representatives • • Homo habilis Homo erectus Later Homo representatives • • Neandertals Cro-Magnons 37 23.5 Evolution of Humans Human evolution Figure 23.16 Human evolution. 38 23.5 Evolution of Humans Early Homo: Homo habilis • Lived 2.0-1.9 MYA • Large brain with enlarged speech area • Omnivorous (hunters and gatherers) • Primitive tools • May have had culture 39 23.5 Evolution of Humans Early Homo: Homo erectus • • • • • • • • Lived 1.9-0.3 MYA Larger brain than H. habilis Flat face with the nose projected Tall and stood erect Striding gait May have migrated from Africa to Europe and Asia Advanced tools and fire (systematic hunters) May have had language 40 23.5 Evolution of Humans Homo ergaster Figure 23.17 Homo ergaster. 41 23.5 Evolution of Humans Modern humans: Homo sapiens • Replacement model, or out-of-Africa hypothesis, is the most widely accepted hypothesis. – – It proposes that modern humans evolved from archaic humans only in Africa. Then, modern humans migrated to Asia and Europe, where they replaced the archaic species about 100,000 years BP. 42 23.5 Evolution of Humans Hypothesis for modern human evolution Figure 23.18 Replacement model. 43 Migration of early Homo from Africa 44 23.5 Evolution of Humans Neandertals • Discovered in Germany 200,000 years ago • Massive brow ridges • Nose, jaws, and teeth protrude forward • Low and sloping forehead, no chin 45 23.5 Evolution of Humans Cro-Magnons • • • • • Lived about 40,000 to 100,000 years ago Oldest fossils to be designated Homo sapiens Modern appearance Advanced culture including art, tools, and maybe language Good cooperative hunters 46 23.5 Evolution of Humans Cro-Magnons Figure 23.19 The Cro-Magnons. 47 23.5 Evolution of Humans Human variation • • Human variations between populations are called ethnicities. Variations evolved as adaptation to local environments. – Skin color ranges from dark to light. – Body shape • • Bergmann’s rule – colder regions mean bulkier build Allen’s rule – colder regions mean shorter limbs, digits, and ears 48 23.5 Evolution of Humans Human variation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Figure 23.20 Ethnic variations in modern humans. b. c. © PhotoDisc/Getty RF; 22.20b: © Sylvia S. Mader; c: © Adam Crowley/Getty Images 49