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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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11 1 impacts issues reflections of a distant past
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
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 inference4
From Evidence to Inference
  • Barringer crater, Arizona
pioneers of biogeography
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
  • Wallace and Darwin thought similarities in birds on different continents might indicate a common ancestor
  • Some plants that lived in similar climates on different continents had similar features, but were not closely related
comparative morphology
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
  • 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
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
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
  • 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
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
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
Shared Traits
  • Darwin collected fossils of extinct glyptodons, which shared traits with modern armadillos
limited resources
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
  • 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
  • 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
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
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
Alfred Wallace
  • The codiscoverer of natural selection
11 4 about fossils
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
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
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
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
  • 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
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
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
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




stem reptile





Fig. 11-12, p. 208

morphological convergence
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









limbs with 5 digits

Fig. 11-13d, p. 209

comparative embryology
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
11 7 biochemical similarities
11.7 Biochemical Similarities
  • Each lineage has unique characters that are a mixture of ancestral and novel traits, including biochemical features such as the nucleotide sequence of DNA
  • We can discover and clarify evolutionary relationships through comparisons of nucleic acid and protein sequences