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PowerPoint® Lecture Presentations for
BiologyEighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Descent with Modification: A Darwinian View of Life
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Overview: Endless Forms Most Beautiful
• A new era of biology began in 1859 when Charles Darwin published The Origin of Species
• The Origin of Species focused biologists’ attention on the great diversity of organisms
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• Darwin noted that current species are descendants of ancestral species
• Evolution can be defined by Darwin’s phrase descent with modification
• Evolution can be viewed as both a pattern and a process
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survivorship at extreme conditions
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• To understand why Darwin’s ideas were revolutionary, we must examine them in relation to other Western ideas about Earth and its life
Concept 1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species
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Scala Naturae and Classification of Species
• The Greek philosopher Aristotle (384-322 B.C.) viewed species as fixed and arranged them on a scala naturae
• The Old Testament holds that species were individually designed by God and therefore perfect
• Carolus Linnaeus (1707-1778) saw the adaptations as evidence that God had designed each species for a specific purpose. He created taxonomy.
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Ideas About Change over Time
• 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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the lower the strata the older thesample
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• Georges Cuvier developed Paleontology, he advocated catastrophism, speculating that each boundary between strata represents a catastrophe
• Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today
• Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time
• This view strongly influenced Darwin’s thinking
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Lamarck’s Hypothesis of Evolution
• Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics
• The mechanisms he proposed are unsupported by evidence
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Bonsai trees are "trained" to be dwarf, a seed will produce a normal sized tree
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• As the 19th century dawned, it was generally believed that species had remained unchanged since their creation
• However, a few doubts about the permanence of species were beginning to arise
Concept 2: Descent with Modifications by Natural Selection explains adaptations of organisms and the unity and diversity of life
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Darwin’s Research
• Charles Darwin had a consuming interest in nature through out his life
• After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle
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The Voyage of the Beagle
• During his travels on the Beagle, Darwin collected specimens of South American plants and animals
• He observed adaptations of plants and animals that inhabited many diverse environments
• Darwin was influenced by Lyell’s Principles of Geology and thought that the earth was more than 6000 years old
• His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America
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Fig. 22-5
NORTHAMERICA
EUROPE
AFRICA
AUSTRALIA
GREATBRITAIN
SOUTHAMERICA
ATLANTICOCEAN
PACIFICOCEAN Cape of
Good Hope
Tierra del FuegoCape Horn
TasmaniaNewZealand
Equator
TheGalápagosIslands
Pinta
MarchenaGenovesa
Santiago DaphneIslands
PinzónFernandina
IsabelaSan
Cristobal
SantaFe
SantaCruz
Florenza Española
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Fig. 22-5b
TheGalápagosIslands
Pinta
MarchenaGenovesa
SantiagoDaphneIslands
PinzónFernandina
IsabelaSan
Cristobal
SantaFe
SantaCruz
Florenza Española
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Darwin’s Focus on Adaptation
• In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes
• From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches
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Fig. 22-6
(a) Cactus-eater (c) Seed-eater
(b) Insect-eater
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The Origin of Species
• Darwin developed two main ideas:
– Descent with modification explains life’s unity and diversity
– Natural selection is a cause of adaptive evolution
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Descent with Modification
• Darwin never used the word evolution in the first edition of The Origin of Species
• The phrase descent with modificationsummarized Darwin’s perception of the unity of life
• The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past
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• In the Darwinian view, the history of life is like a tree with branches representing life’s diversity
• Darwin’s theory meshed well with the hierarchy of Linnaeus
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Fig. 22-8Hyracoidea(Hyraxes)
Sirenia(Manateesand relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Elephas maximus(Asia)
Stegodon
Mammuthus
Loxodontaafricana(Africa)
Loxodonta cyclotis(Africa)
010425.52434
Millions of years ago Years ago
Platybelodon
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Artificial Selection, Natural Selection, and Adaptation
• Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection
• Darwin then described four observations of nature and from these drew two inferences
• Observation #1: Members of a population often vary greatly in their traits
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Fig. 22-9
Kale
Kohlrabi
Brussels sprouts
Leaves
Stem
Wild mustard
Flowersand stems
Broccoli
Cauliflower
Flowerclusters
Cabbage
Terminalbud
Lateralbuds
Brassica olerasia
var. capitata var. gemmifera
var. acephalavar. botrytis
var. italica var. gogylodes
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• Observation #2: Traits are inherited from parents to offspring
• Observation #3: All species are capable of producing more offspring than the environment can support
• Observation #4: Owing to lack of food or other resources, many of these offspring do not survive
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• Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
• "The higher chances of survival, the more offspring they have"
• example: fishes, frogs, birds, insects
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• Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
• "Those that survive will bring the favorable traits with them"
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• Note that individuals do not evolve; populations evolve over time
• Natural selection can only increase or decrease heritable traits in a population
• Adaptations vary with different environments
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Concept 3: Evolution is supported by an overwhelming amount of scientific evidence
• New discoveries continue to fill the gaps identified by Darwin in The Origin of Species
• Direct Observations of Evolutionary Change
– evolution of drug-resistant TB and MRSA
– color change in moths, from light to dark due to pollution
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• Natural selection does not create new traits, but edits or selects for traits already present in the population
• The local environment determines which traits will be selected for or selected against in any specific population
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The Fossil Record
• The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time
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Fig. 22-15
Bristolia insolens
Bristolia bristolensis
Bristolia harringtoni
Bristolia mohavensis
Latham Shale dig site, SanBernardino County, California
0
2
4
6
8
10
12
14
16
18
1
2
3
3
3
1
2
44
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• The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record
• Paleontologists have discovered fossils of many such transitional forms
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Fig. 22-16
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
(c) Dorudon (fully aquatic)
Pelvis andhind limb
Pelvis andhind limb
(d) Balaena (recent whale ancestor)
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Homology
• Homology is similarity resulting from common ancestry
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Anatomical and Molecular Homologies
• Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor
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Humerus
Radius
UlnaCarpals
Metacarpals
Phalanges
Human Cat Whale Bat
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• Comparative embryology reveals anatomical homologies not visible in adult organisms
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Pharyngealpouches
Post-analtail
Chick embryo (LM) Human embryo
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• Vestigial structures are remnants of features that served important functions in the organism’s ancestors
• Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor
– tail in human embryo
– teeth in birds
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Homologies and “Tree Thinking”
• The Darwinian concept of an evolutionary tree of life can explain homologies
• Evolutionary trees are hypotheses about the relationships among different groups
• Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data
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Fig. 22-19
Hawks andother birds
Ostriches
Crocodiles
Lizardsand snakes
Amphibians
Mammals
Lungfishes
Tetrapod limbs
Amnion
Feathers
Homologouscharacteristic
Branch point(common ancestor)
Birds6
5
4
3
2
1
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Fig. 22-UN1
Observations
Over time, favorable traitsaccumulate in the population.
Inferences
and
Individuals in a populationvary in their heritable
characteristics.
Organisms produce moreoffspring than the
environment can support.
Individuals that are well suitedto their environment tend to leave
more offspring than other individuals
The End
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Convergent Evolution
• Convergent evolution is the evolution of similar, or analogous, features in distantly related groups
• Analogous traits arise when groups independently adapt to similar environments in similar ways
• Convergent evolution does not provide information about ancestry
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Fig. 22-20
Sugarglider
Flyingsquirrel
AUSTRALIA
NORTHAMERICA
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Biogeography
• Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution
• Islands have many endemic species that are often closely related to species on the nearest mainland or island
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• Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift
• An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved
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What Is Theoretical About Darwin’s View of Life?
• In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena
• Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions
• Ongoing research adds to our understanding of evolution
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