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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
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
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
Fig. 11-7a, p. 202
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. 11-7b, 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. 11-7c, 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.
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)
Fig. 11-12, p. 208
pterosaur
chicken
penguin
stem reptileporpoise
bat
human
elephant
Morphological Divergence Among Vertebrate Forelimbs
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
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