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Evidence of Evolution. Chapter 11. 11.1 Impacts/Issues Reflections of a Distant Past. Events of the ancient past can be explained by the same physical, chemical, and biological processes that operate in today’s world. From Evidence to Inference.
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Evidence of Evolution Chapter 11
11.1 Impacts/IssuesReflections of a Distant Past • Events of the ancient past can be explained by the same physical, chemical, and biological processes that operate in today’s world
From Evidence to Inference • Scientists infer from evidence that an asteroid impact near the Yucatán 65 million years ago caused the mass extinction of dinosaurs • Mass extinction • Simultaneous loss of many lineages from Earth
From Evidence to Inference • Barringer crater, Arizona
Pioneers of Biogeography • Late 1800s: Charles Darwin, Alfred Wallace and other naturalists observed patterns in where species live, how they might be related, and how natural forces might shape life • Biogeography • Study of patterns in the geographic distribution of species and communities
Biogeography • Wallace and Darwin thought similarities in birds on different continents might indicate a common ancestor
Biogeography • Some plants that lived in similar climates on different continents had similar features, but were not closely related
Comparative Morphology • Naturalists studying body plans were confused by vestigial body parts with no apparent function • Comparative morphology • Scientific study of body plans and structures among groups of organisms
Geology • Identical rock layers in different parts of the world, sequences of similar fossils, and fossils of giant animals with no living representatives also puzzled early naturalists
Confusing Discoveries • Taken as a whole, findings from biogeography, comparative morphology, and geology did not fit with prevailing beliefs of the 19th century • Increasingly extensive observations of nature led to new ways of thinking about the natural world
11.3 A Flurry of New Theories • Nineteenth-century naturalists tried to explain the accumulating evidence of evolution • Georges Cuvier proposed that catastrophic geologic forces unlike those of the present day shaped Earth’s surface (catastrophism) • Jean-Baptiste Lamarck proposed that changes in an animal over its lifetime were inherited
Evolution • Naturalists suspected that environmental factors affected affect a species’ traits over time, causing changes in a line of descent • Evolution • Change in a line of descent (in a line from an ancestor)
Voyage of the Beagle • 1831: Charles Darwin set out as a naturalist on a five-year voyage aboard the Beagle • He found many unusual fossils and observed animals living in many different environments
Lyell’s Theory of Uniformity • Darwin was influenced by Charles Lyell’s Principles of Geology, which set forth the theory of uniformity – in contrast to catastrophism • Theory of uniformity • Idea that gradual repetitive processes occurring over long time spans shaped Earth’s surface
Shared Traits • Darwin collected fossils of extinct glyptodons, which shared traits with modern armadillos
Limited Resources • Thomas Malthus observed that: • A population tends to grow until it begins to exhaust environmental resources—food, shelter from predators, etc • When resources become scarce, individuals must compete for them • Darwin applied these ideas to the species he had observed on his voyage
Fitness • Darwin realized that in any population, some individuals have traits that make them better suited to the environment than others, and therefore more likely to survive and reproduce • Fitness • The degree of adaptation to an environment, as measured by an individual’s relative genetic contribution to future generations
Adaptation • Adaptive traits that impart greater fitness to an individual become more common in a population over generations, compared with less competitive forms • Adaptation (adaptive trait) • A heritable trait that enhances an individual’s fitness
Natural Selection • Darwin concluded that the process of natural selection, through variations in fitness and adaptation, is a driving force of evolution • Natural selection • Differential survival and reproduction of individuals of a population that vary in the details of shared, heritable traits
Great Minds Think Alike • Alfred Wallace, the “father of biogeography”, proposed the theory of natural selection in 1858, at the same time as Darwin • Darwin published On the Origin of Species the following year, in which he described descent with modification, or evolution
Alfred Wallace • The codiscoverer of natural selection
11.4 About Fossils • Fossils • Physical evidence of organisms from the past • Hard fossils include mineralized bones, teeth, shells, spores and other hard body parts • Trace fossils include footprints, nests, trails, feces and other evidence of activities
A A 30-million-year-old fossil of Elomeryx. This small terrestrial mammal was a member of the same artiodactyl group that gave rise to hippopotamuses, pigs, deer, sheep, cows, and whales. Fig. 11-7a, p. 202
B Rodhocetus, an ancient whale, lived about 47 million years ago. Its distinctive ankle bones point to a close evolutionary connection to artiodactyls. Inset: compare a Rodhocetus ankle bone (left) with that of a modern artiodactyl, a pronghorn antelope (right). Fig. 11-7b, p. 202
C Dorudonatrox, an ancient whale that lived about 37 million years ago. Its artiodactyl-like ankle bones (left) were much too small to have supported the weight of its huge body on land, so this mammal had to be fully aquatic. Fig. 11-7c, p. 202
11.5 Putting Time Into Perspective • Transitions in the fossil record, found in characteristic layers of sedimentary rock, became boundaries for great intervals of the geologic time scale • Geologic time scale • Chronology of Earth history • Correlates with evolutionary events
Drifting Continents, Changing Seas • Theory of continental drift • Earth’s continents were once part of a single supercontinent that split up and drifted apart • Explains how the same types of fossils can occur on both sides of an ocean • Pangea • Supercontinent that formed about 237 million years ago and broke up about 152 million year ago
Plate Tectonics: A Mechanism of Continental Drift • Theory of plate tectonics • Earth’s outer layer of rock is cracked into plates • Slow movement rafts continents to new positions over geologic time • Where plates spread apart, molten rock wells up from deep inside the Earth and solidifies • Where plates collide, one slides under the other and is destroyed
Gondwana • Certain fossils of ferns and reptiles that predate Pangea are found in similar rock layers in Africa, India, South America, and Australia – evidence of an even earlier supercontinent • Gondwana • Supercontinent that formed more than 500 million years ago
Impacts on Evolution • Evidence suggests that supercontinents have formed and broken up at least five times • The resulting changes in the Earth’s surface, atmosphere, waters and climates have had profound impacts on evolution
11.6 Similarities in Body Form and Function • Similarities in structure of body parts are often evidence of a common ancestor • Homologous structures • Similar body parts that reflect shared ancestry • May be used for different purposes in different groups, but the same genes direct their development
Morphological Divergence • A body part that appears very different in appearance may be quite similar in underlying aspects of form – evidence of shared ancestry • Morphological divergence • Evolutionary pattern in which a body part of an ancestor changes in its descendants (homologous structures)
Morphological Divergence Among Vertebrate Forelimbs pterosaur chicken penguin stem reptile porpoise bat human elephant Fig. 11-12, p. 208
Morphological Convergence • Some body parts look alike in different lineages, but did not evolve in a common ancestor • Analogous structures • Similar structures that evolved separately in different lineages • Morphological convergence • Evolutionary pattern in which similar body parts evolve separately in different lineage
Insects Bats Humans Crocodiles Birds wings wings wings limbs with 5 digits Fig. 11-13d, p. 209
Comparative Embryology • Embryos of related species tend to develop in similar ways • Similarities in patterns of embryonic development are the result of master genes (homeotic genes) that have been conserved over evolutionary time
