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Human Biology Sylvia S. Mader Michael Windelspecht Chapter 22 Human Evolution Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Points to Ponder • • • • • • • • • • • • • • What is the chemical evolution of life? 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. How are humans classified? What characteristics do primates have in common? Explain the evolution of hominids. Who is Lucy? Explain the evolution of humans. What are the 2 hypotheses for modern man? Compare and contrast Cro-Magnons and Neandertals 22.1 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 and is supported by the fact that RNA can act as enzymes called ribozymes (RNA-first hypothesis) 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 22.1 Origin of life Origin of life through chemical evolution Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2 CO2 CO2 N2 H2O N2 a. The primitive atmosphere contained gases, including H2O, CO2, and N2, that escaped from volcanoes. As the water vapor cooled, some gases were washed into the oceans by rain. CO2 H2O CO2 CO2 N2 CO2 CO2 H2 N2 fatty acids N2 N2 H2O purines nucleotides glucose pyrimidines CO2 H2O H2O CO2 N2 H2O N2 glucose nucleic acids proteins CO2 protocells H2O H2 amino acids N2 H2 b. The availability of energy from volcanic eruption and lightning allowed gases to form small organic molecules, such as nucleotides and amino acids. N2 nucleotides amino acids H2O c. Small organic molecules could have joined to form proteins and nucleic acids, which became incorporated into membrane-bound spheres. The spheres became the first cells, called protocells. Later protocells became true cells that could reproduce. 22.2 Biological evolution Biological evolution • Biological evolution – change in population or species over time • 2 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 makes an organism to survive and reproduce in its environment 22.2 Biological evolution Evidence to support the theory of evolution by common descent 1. 2. 3. 4. Fossils in the fossil record Biogeographical evidence Anatomical evidence Biochemical evidence 22.2 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 22.2 Biological evolution What have we learned from the fossil record? • 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 22.2 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. Present 10 MYA feathers Moderntoothed whales wing 20 MYA head 30 MYA wing Rodhocetus kasrani’s reduced hind limbs could not have aided it in walking or swimming. Rodhocetus swam with an up-and-down motion, as do modern whales. 40 MYA teeth tail with vertebrae Ambulocetus natans probably walked on land (as do modern sea lions) and swam by flexing its backbone and paddling with its hind limbs (as do modern otters). 50 MYA claws feet tail reptile characteristics 60 MYA Archaeopteryx fossil artist depiction of Archaeopteryx (fossil, left): © Jean-Claude Carton/Bruce Coleman/PhotoShot; (drawing, right): © Joe Tucciarone bird characteristics Hypothetical mesonychid skeleton 22.2 Biological evolution 2. Biogeographical evidence • Is the study of the distribution of plants and animals throughout the world • Supports the hypothesis that organisms originate in one locale and then may spread out • Different life forms are expected whenever geography separates them • Islands demonstrate this because they have many unique life forms because of geographic isolation 22.2 Biological evolution Patagonian hare and European rabbit 22.2 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 • 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 but are reduced and may have no function in another group e.g., Whales have a vestigial pelvic girdle and legs 22.2 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 cat horse human 22.2 Biological evolution Homologous structures in vertebrate embryos Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pig embryo pharyngeal pouches postanal tail Chick embryo (both): © Carolina Biological Supply/Phototake 22.2 Biological evolution 4. Biochemical evidence • Almost all living things use the same biochemicals (e.g., DNA and ATP) • Living things use the same triplet code • Living things use the same 20 amino acids in their proteins • Living things share many of the same genes 22.2 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 30 moth 51 yeast 22.2 Biological evolution Natural selection • A theory by Darwin that describes a mechanism by which a species becomes adapted to its environment • 3 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 22.2 Biological evolution Natural selection Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lamarck’s proposal 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. 22.3 Classification of humans The arrival of humans on earth 22.3 Classification of humans Three 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 common ancestor 22.3 Classification of humans Primates • Characteristics: • • • • • • Opposable thumb Stereoscopic vision (depth perception) Well-developed brain Reduced # of offspring (usually a single birth) with an increased period of parental care Emphasis on learned behavior and social interactions Two suborders: • • Prosimians – includes lemurs, tarsiers, and lorises Anthropoids – includes monkeys, apes, and humans 22.3 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. 22.4 Evolution of hominids 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 60 50 40 30 20 Million years Ago (MYA) 10 PRESENT Prosimians Anthropoids New World Monkeys 22.4 Evolution of hominins Evolution of hominins • Hominids – All species of the genus Homo and their close relatives • Characteristics: • • • • Bipedal Flatter face with more pronounced chin Brain size 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 22.4 Evolution of hominids Australopithecines • A group of hominins that evolved and diversified in Africa 3 MYA • • • • Some had slight frames and others were robust with massive jaws that fed on plant materials Walked upright Limbs proportions are ape-like Small brain • Famous skeleton named “Lucy” is from this group • Australopithecus africanus has a large brain is the most likely ancestral candidate for early Homo 22.4 Evolution of hominids Australopithecines 22.5 Evolution of humans Characteristics of Homo 1. Brain size is 600 cm3 or greater 2. Evidence of tool use 3. Jaw and teeth resemble humans Early Homo representatives: • • Homo habilis Homo erectus Later Homo representatives: • • Neandertals Cro-Magnons 22.5 Evolution of humans Human evolution Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sahelanthropus tchadensis Australopithecus afarensis Homo habilis Paranthropus robustus Homo sapiens Homo sapiens Homo neandertalensis Homo heidelbergensis Homo erectus Homo ergaster Homo rudolfensis Australopithecus garhi Homo habilis Australopithecus africanus Australopithecus afarensis Australopithecus anamensis Paranthropus aethiopicus Paranthropus boisei Ardipithicus ramidus Paranthropus robustus Sahelanthropus tchadensis 7.5 7 6.5 6 5.5 5 4.5 4 3.5 Million Years Ago (MYA) 3 2.5 2 1.5 1 0.5 0 22.5 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 • Culture may have existed 22.5 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) Language may have evolved 22.5 Evolution of humans Later Homo individual Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. neck of femur femur © National Museum of Kenya 22.5 Evolution of humans Modern Humans: Homo sapiens • 2 hypotheses: 1. Multiregional continuity – suggests that modern humans evolved from H. erectus in several geographic places 2. Out-of-Africa hypothesis – modern humans evolved from H. erectus most likely only in Africa and later migrated to Europe and Asia (this hypothesis has the most support) 22.5 Evolution of humans Hypotheses for modern human evolution Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ASIA AFRICA EUROPE ASIA 0.1 AFRICA EUROPE Homo sapiens Homo sapiens 0.1 Homo sapiens Homo sapiens Homo sapiens Homo sapiens interbreeding 1 interbreeding 2 migration of Homo ergaster migration of Homo ergaster Millions of Years Ago (MYA) Millions of Years Ago (MYA) Homo ergaster evolves into modern humans in Asia, Africa, and Europe. Homo sapiens 1 2 migration of Homo ergaster migration of Homo ergaster Homo ergaster Homo ergaster a. Multiregional continuity Modern humans evolve in Africa and migrate to Asia and Europe. b. Out of Africa 22.5 Evolution of humans Neandertals • Discovered in Germany 2000 years ago • Massive brow ridges • Nose, jaws and teeth protrude forward • Low and sloping forehead, no chin 22.5 Evolution of humans Cro-Magnons • Lived about 40,000 to 10,000 years ago • Oldest fossils to be designated Homo sapiens • Modern appearance • Advanced culture including art, tool and maybe language • Good cooperative hunters 22.5 Evolution of humans Human variation • Human variations between populations are called ethnicities • Variations evolved as adaptation to local environments: – Skin color: range of dark to light – Body shape: Bergmann’s rule and Allen’s rule 22.5 Evolution of humans Human variation