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
 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
Vestigial Body Parts
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
Comparative pelvic anatomy
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
Darwin and the Voyage of the Beagle
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
Principles of Natural
Selection
The Galapagos Islands
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
Plate Tectonics
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
Morphological Convergence
Insects
Bats
Humans
Crocodiles
wings
Birds
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
Comparative Embryology
Fig. 11-14a, p. 210
Fig. 11-14b, p. 210
Fig. 11-14c, p. 210
Fig. 11-14d, p. 210
Fig. 11-14e, p. 210
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