copyright © 2005 pearson education, inc. publishing as benjamin cummings ch. 22 descent with...
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Ch. 22
Descent with Modification
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• The Origin of Species
– Focused biologists’ attention on the great diversity of organisms
Figure 22.1
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• The Origin of Species
– challenged traditional views of a young Earth inhabited by unchanging species
– Shook the deepest roots of Western culture
– Challenged a worldview that had been prevalent for centuries
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• Darwin
– said many species of organisms are descendants of ancestral species
– proposed natural selection as a mechanism for evolution
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• The historical context of Darwin’s life and ideas
Figure 22.2
Linnaeus (classification)Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, nutural selection)
Mendel (inheritance)
Wallace (evolution, natural selection)
1750
American Revolution French Revolution U.S. Civil War
1800 1850 19001795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his theory of evolution.1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
Darwin begins his notebooks on the origin of species.1837Darwin writes his essay on the origin of species.1844
Wallace sends his theory to Darwin.1858
The Origin of Species is published.1859Mendel publishes inheritance papers.1865
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The Scale of Nature and Classification of Species
• The Greek philosopher Aristotle (384-322 BC)
– viewed species as fixed and unchanging
– said life forms could be arranged according to increasing complexity
• The Old Testament of the Bible
– states that species were individually designed by God
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• Carolus Linnaeus (1707-1778)
– Grouped similar species into increasingly general categories reflecting what he considered the pattern of their creation
• a founder of taxonomy - the branch of biology dedicated to the naming and classifying of organisms
• Developed binomial nomenclature – a two-part naming system that includes the organism’s genus and species
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Fossils, Cuvier, and Catastrophism
• The study of fossils
– Helped to lay the groundwork for Darwin’s ideas
• Fossils are remains or traces of organisms from the past
– Usually found in sedimentary rock, which appears in layers or strata
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• Georges Cuvier (1769-1832)
– Developed paleontology, the study of fossils
– opposed the idea of gradual evolutionary change
– advocated catastrophism
• says that events in the past occurred suddenly and by different mechanisms than those occurring today
• This explained boundaries between strata and the location of different species
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Theories of Gradualism
• Gradualism
– the idea that profound change can take place through the cumulative effect of slow but continuous processes
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• Geologists Hutton and Lyell (1797-1875)
– Developed the principle of uniformitarianism, the idea that the geologic processes that have shaped the planet have not changed over the course of earth’s history
• Importance: The earth must be very old.
– Exerted a strong influence on Darwin’s thinking
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Lamarck’s Theory of Evolution
• Lamarck (1744-1829) hypothesized that species evolve.
– Through use and disuse – parts of the body that are used extensively become larger and larger while those not used deteriorate.
– Acquired characteristics are inherited.
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Comparison of Lamarck and Darwin
Lamarck Darwin
Use and disuse Variation
Transmission of Acquired characteristics
Inheritance
Increasing complexity Differential survival
No extinction extinction
Lamarck recognized that species evolve but his explanation of how evolution occurs was flawed.
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Darwin’s Research
• Charles Darwin
– Had a strong interest in nature
– After receiving his B.A. degree, he was accepted on board the HMS Beagle, which was about to embark on a voyage around the world
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The Voyage of the Beagle
• During his travels on the Beagle, Darwin
– collected many specimens of South American plants and animals
– observed adaptations of plants and animals in many diverse environments
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The Beagle’s stop at the Galápagos Islands near the equator west of South America sparked Darwin’s interest in the geographic distribution of species.
EnglandEUROPE
NORTHAMERICA
GalápagosIslands
Darwin in 1840,after his return
SOUTHAMERICA
Cape ofGood Hope
Cape Horn
Tierra del Fuego
AFRICA HMS Beagle in port
AUSTRALIA
Tasmania
NewZealand
PACIFICOCEAN
An
des
ATLANTICOCEAN
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Darwin’s Focus on Adaptation
• During and after the voyage of the Beagle,
– Darwin began to see a link between adaptation to different environments and the origin of new species
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• From studies made years after Darwin’s voyage, biologists concluded that this is what happened to the Galápagos finches
Figure 22.6a–c
(a) Cactus eater. The long,sharp beak of the cactusground finch (Geospizascandens) helps it tearand eat cactus flowersand pulp.
(c) Seed eater. The large groundfinch (Geospiza magnirostris)has a large beak adapted forcracking seeds that fall fromplants to the ground.
(b) Insect eater. The green warbler finch (Certhidea olivacea) uses itsnarrow, pointed beak to grasp insects.
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• 1844: Darwin wrote an essay on the origin of species and natural selection
– reluctant to introduce his theory publicly, anticipating the uproar it would cause
• 1858: Darwin received a manuscript from Alfred Russell Wallace who had developed a theory of natural selection similar to Darwin’s
• 1859: Darwin quickly finished The Origin of Species And published it the next year
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• In the Darwinian view, the history of life is like a tree
– With multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms
Hyracoidea(Hyraxes)
Sirenia(Manatees
and relatives)
Yea
rs a
goM
illio
ns
of y
ea
rs a
go
Dei
no
ther
ium
Ma
mm
ut
Ste
go
don
Ma
mm
uth
us
Pla
tyb
elo
don
Bar
yth
eriu
m
Mo
eri
ther
ium
Elephasmaximus
(Asia)
Loxodontaafricana(Africa)
Loxodontacyclotis(Africa)
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Natural Selection
• Adaptations– Heritable characteristics that enhance
organisms’ ability to survive and reproduce in specific environments.
Desert fox: large ears radiate heat. Arctic fox: small ears conserve heat.
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For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully.
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Overproduction
• Production of more individuals than the environment can support
• Leads to a competition for resources
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Variations in traits occur
Members of a population vary extensively in their characteristics. No two individuals are exactly alike
Figure 22.9
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Survival depends on inherited traits and the resources available in the environment.
• Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals
• This leads to a gradual change in a population, with favorable characteristics accumulating over generations
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Summary of Natural Selection
• Natural selection is differential success in reproduction
– results from the interaction between individuals that vary in heritable traits and their environment
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• Natural selection can produce an increase over time in the adaptation of organisms to their environment.
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Artificial Selection
– Humans have modified species over many generations by selecting and breeding individuals that possess desired traits
Figure 22.10
Terminalbud
Lateralbuds
Brussels sproutsCabbage
Flowercluster
Leaves
Cauliflower
Flowerandstems
Broccoli Wild mustard Kohlrabi
Stem
Kale
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Artificial Selection - breeding
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• If an environment changes over time
– Natural selection may result in populations adapting to these new conditions.
• Populations adapt NOT individual organisms.
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The Evolution of Drug-Resistant HIV
• In humans, the use of drugs
– Selects for pathogens that through chance mutations are resistant to the drugs’ effects
• Natural selection is a cause of adaptive evolution
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• Researchers have developed numerous drugs to combat HIV
– But using these medications selects for viruses resistant to the drugs
Figure 22.13
PatientNo. 1
Patient No. 2
Patient No. 3
Per
cen
t of
HIV
res
ista
nt
to 3
TC
Weeks
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• The ability of bacteria and viruses to evolve rapidly
– Poses a challenge to our society
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Homology, Biogeography, and the Fossil Record
• Evolutionary theory
– Provides a cohesive explanation for many kinds of observations
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Homology
• Homology
– Is similarity resulting from common ancestry
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Anatomical Homologies
• Homologous structures between organisms
– variations on a structure that was present in a common ancestor
Figure 22.14Human Cat Whale Bat
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Comparative embryology
– Reveals anatomical homologies not visible in adult organisms
Figure 22.15
Pharyngealpouches
Post-analtail
Chick embryo Human embryo
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Vestigial organs
remnants of structures that served important functions in the organism’s ancestors
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Molecular Homologies
• Biologists can observe homologies among organisms at the molecular level
– Such as genes that are shared among organisms inherited from a common ancestor
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Homologies and the Tree of Life
• The Darwinian concept of an evolutionary tree of life
– Can explain the homologies that researchers have observed
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• Anatomical resemblances among species
– Are generally reflected in their molecules, their genes, and their gene products
Figure 22.16
Species
Human
Rhesus monkey
Mouse
Chicken
Frog
Lamprey14%
54%
69%
87%
95%
100%
Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide
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Biogeography
• Darwin’s observations of the geographic distribution of species, biogeography
– Formed an important part of his theory of evolution
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Sugarglider
AUSTRALIA
NORTHAMERICA
Flyingsquirrel
Figure 22.17
• Some similar mammals that have adapted to similar environments
– Have evolved independently from different ancestors
https://www.youtube.com/watch?v=1-FHzf4xnWw
https://www.youtube.com/watch?v=cHa8jrxdF_4
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The Fossil Record• The Darwinian view of life
– Predicts that evolutionary transitions should be found in the fossil record
• Paleontologists have discovered fossils of many such transitional forms.
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Theory of Evolution
• In science, a theory
– Accounts for many observations and data and attempts to explain and integrate a great variety of phenomena
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