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Principles of Evolution
Chapter 23
23.1 A Little Evolutionary History
Fun fact: In Latin, the word evolution
means “unrolling”
History of Evolution
 Evolution
• Genetic change in a line of descent through
successive generations
• Millions of species
• All share a common ancestor
• origin of the Earth’s many species was
a disputed topic
Binomial Nomenclature
Hierarchy of groups that a
species belongs to:
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Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
 Two part name:
• Genus
• Species
 Correct format:
• Genus capitalized
• Species NOT capitalized
• Both in italics
Homo sapien
Classification of Humans
The Primates Include Several Nonhuman
Species
History of Evolution
 Charles Darwin
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Naturalist on the HMS Beagle (1831–1836)
Studied geology and collected marine life
Talked to other naturalists
Influenced by Thomas Malthus
• A population tends to outgrow its resources
• Members must compete for what is available; yet,
over time populations remain stable
• Natural selection theory
Natural Selection Can Reshape the
Genetic Makeup of a Population
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Theory of evolution by natural selection
1. The individuals of a population vary in their body
form, functioning, and behavior
2. Many variations can be passed from generation
to generation
3. In every set of circumstances, some versions of
a trait are more advantageous than others
4. Natural selection is the difference in survival
and reproduction
Natural Selection Can Reshape the
Genetic Makeup of a Population
5. A population is evolving when some forms of a
trait are becoming more or less common
6. Over time, shifts in the makeup of gene pools
lead to amazing diversity of life forms
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Adaptation
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Over time, organisms come to have traits that
suit them to the conditions in a particular
environment
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Helps species survive!
Darwin’s Long Voyage on the Beagle
Spurred His Thinking about Evolution
Animation: The Galapagos Islands
Animation: Finches of the Galapagos
23.2 A Key Evolutionary Idea:
Individuals Vary
Focus: Evolution occurs in
populations of organisms and begins
when the genetic makeup of a
population changes.
Evolution
 Life on Earth spans about 4 billion years
 Microevolution
• Cumulative genetic changes that may give rise to
new species within the same genus
 Macroevolution
• Large-scale patterns, trends, and rates of change
among various groups of species
Animation: Milestones in the history of
life
Major Processes of Microevolution
Individuals Don’t Evolve—Populations Do
 Population
• Group of individuals of the same species
occupying a given area
• Similar morphological traits
• Similar physiological traits
• Similar behavioral traits
Humans Show a Great Deal of Variation
in Their Outward Appearance
Genetic Differences Produce Variation
 Gene pool
• All of the genetic material within a population
• Chromosomes
• DNA
• Slightly different forms of genes produce
variations
23.3 Microevolution: How New Species
Arise
Focus: Most people carry several mutations.
From the perspective of evolution,
mutations are important because they
are the source of alleles — the
alternative forms of genes.
Mutation Produces New Forms of Genes
 Mutation: alterations of the gene (hereditary)
• Harmful
• Affected individual can’t survive or reproduce as
well as others
• Beneficial
• Affected individuals have improved chances of
survival and reproduction
• Neutral
• Affected individual does not enhance survival or
reproduction of the individual
• MOST COMMON!
Chance Can Also Change a Gene Pool
 Genetic drift
• Chance events that adjust alleles in a gene pool
• Founder effect
• Change is more rapid in small populations
• Finns
 Gene flow
• Physical movement of alleles in and out of
populations
• Little gene flow in Finland
The Ability to Interbreed Defines a
Species
 Species (defined)
• In sexual organisms, populations can interbreed
naturally and produce fertile offspring
 Speciation
• Occurs when gene differences between two
populations prevent interbreeding
Divergence Is the First Step toward the
Formation of New Species
Speciation Can Be Gradual or Sudden
 Gradualism
• New species emerge through many small
changes over time
• Microevolution constantly going on in small steps
 Punctuated equilibrium
• Most evolutionary change occurs in bursts
• Possible causes: changes in climate or some
other aspect of the physical environment
• Fossil evidence provides scanty evidence of
microevolution
Animation: Directional selection
23.4 Looking at Fossils and
Biogeography
Focus: The fossil record and
biogeography are important tools in
reconstructing the intertwined journey
of life and Earth.
Fossils
 Recognizable, physical
evidence of ancient life
 Similarities and
differences among
fossils and living
organisms:
• Evidence of natural
selection and adaption
High-Quality Fossils Such as These
Are Rare
Fossils Are Found in Sedimentary Rock
Hard parts of organisms can become fossils,
• e.g., bones, teeth, shells, and seeds
 Fossilization
• Begins when an organism is buried in silt,
volcanic ash, or sediments
• Water seeps into the organic remains, infusing
them with inorganic material
• Layering of sediments causes stratification in
sedimentary rocks
The Grand Canyon of American Southwest
Reveals Sedimentary Rock Layers
The Fossil Record Is Spotty
 About 250,000 species (only) found as fossils
 Large-scale movement of the Earth’s crust has
destroyed many fossils 
 Fossil record limited to certain environments and
locations
• Fossils that lived near or in shallow seas or
through geologic uplifting
Animation: Geologic forces
The Fossil Record Is Spotty
 Radiometric dating
• Determination of the age of volcanic rock
Animation: Radiometric dating
Biogeography Provides Other Clues
 Biogeography
• Study of the world distribution of plants and
animals
• Why do certain organisms occur where they do?
• Why do the tropics have such a diversity of
organisms?
 Pangea and plate tectonics
• Effect location of organisms
Movements of Crustal Plates Help Explain
Geographical Distribution of Species
Animation: Continental drift
23.5 Comparing the Form and
Development of Body Parts
Focus: Early evolutionary thinkers also noted
patterns in the form of body parts. Modern
biologists have shed light on evolutionary
history by comparing stages of
development in major groups of organisms.
Comparing Body Forms May Reveal
Evolutionary Connections
 Comparative morphology
• Patterns of body form
 Homologous structures:
• Modification of body parts in different lines of
descent from a common ancestor
 Analogous structures:
• Organisms without a recent common ancestor
can have body parts that resemble one another
Animation: Morphological divergence
Development Patterns Also Provide
Clues
 Vertebrates
• Early in development, embryos have similar
stages
• Mutations that altered the onset, rate, or time of
completion of development bring about changes
in the adults of these organisms
 Vestigial structures: “left over” from ancestral
species
• Appendix
• Coccyx
Comparing Embryos Also Provides
Evidence of Evolutionary Relationships
Animation: Comparative embryology
Animation: Mutation and proportional
changes
Vestigial Body Parts Are “Left Over” from
Ancestral Species
23.6 Comparing Genetics
Focus: Genetic similarities and
differences also provide information
about evolutionary connections.
Comparing Genetics
 How closely are species related?
• Outward traits
• DNA, RNA, and proteins
 Primates (example)
• Compare DNA
• OR Compare the amino acid sequence of
hemoglobin
• Cytochrome c
23.7 How Species Come and Go
Focus: The history of life on Earth is
marked by extinction and by the
evolution of new species.
In Extinction, Species Are Lost Forever
 Extinction
• Permanent loss of a species
• Background extinction occurs steadily over time
 Mass extinction
• Sudden, widespread rise in extinctions
• May take 100 million years to recover the number
of species lost
• 6th mass extinction occurring TODAY!
• Human activities and climate change
Many Mass Extinctions Have Occurred
during Earth’s History
today
In Adaptive Radiation, New Species Arise
 Adaptive radiation
• New species of a lineage move into a wide range
of habitats during bursts of microevolution
 Examples:
• Mammals after the dinosaur extinction
• Ancestors of modern man
Proposed Family Tree for Populations of
Modern Humans Native to Different Regions
23.8 Evolution from a Human
Perspective
Focus: Like other life forms, we
humans have a well-defined place in
the evolutionary scheme of things.
Five Trends Mark Human Evolution
1. Precision grip and power grip
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Hands not needed for support
Fingers can wrap around objects
2. Improved daytime vision
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Forward directed eyes
Better at detecting shapes
3. Changes in dentition
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Bow-shaped jaw; teeth of omnivores
Five Trends Mark Human Evolution
4. Changes in the brain and behavior
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Culture: behavior patterns of a social group,
passed between generations by learning
More parental effort on fewer offspring; learning
period became longer
Expansion of cerebral cortex
5. Upright walking
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Bipedalism
Reorganization of the skeletal system; location
of the foramen magnum
Trend toward Longer Life Spans and
Longer Period of Dependency of Young
Compare the Skeletal Organization of
Three Primates
23.9 Emergence of Early Humans
Focus: By 36 million years ago tree-dwelling
primates called anthropoids had evolved in
tropical forests. One or more types were on or
very close to the evolutionary road that would
lead to monkeys, apes, and humans.
Early Hominids Lived in Central Africa
 First hominoids: apelike
• Between 23 and 5 million years ago
• Evolved and spread through Africa, Asia, and
Europe
 Australopithecus afarensis
• Lucy
• Footprints at Laetoli
We Have Fossil Evidence of African
Hominids and Early Humans
Is Homo Sapiens “Out of Africa”?
 Humans
• Genus Homo: 2 million years ago; lived in eastern
Africa
• Larger brain and smaller face than the hominids;
thickly enameled teeth; omnivores
• Made tools
 Homo habilis: handy man
 Homo erectus:
• began leaving Africa for Southeast Asia
Is Homo Sapiens “Out of Africa”?
 Multiregional emergence model
• H. erectus lived in many regions
• Evolved along different paths due to local
selective pressures
 African emergence model
• H. sapiens arose in sub-Saharan Africa between
200,000–100,000 years ago and then left Africa
• They replaced H. erectus in the new regions
• “Out of Africa”
We Have Fossil Evidence of African
Hominids and Early Humans
Estimated Times When Early Homo Sapiens
Groups Were Colonizing Different Regions
Animation: Fossils of australopiths
Animation: Homo skulls
Animation: Primate evolutionary tree
23.10 Earth’s History and the Origin
of Life
Experiments provide indirect evidence
of how life may have emerged on Earth
The Primordial Earth, about 4 Billion
Years Ago, May Have Looked Like This
Conditions on Early Earth Were Intense
 Early atmosphere
• Gaseous: H2, N2, CO, and CO2
• Lacked O2
• Earth’s crust was very hot; cooled and solidified;
H2O condensed into clouds → rain
• Rain stripped mineral salts from rocks and the
early seas formed in depressions in the crust
Biological Molecules Paved the Way for
Cells to Evolve
 Chemical evolution: necessary for formation of
first biological molecules
• Sunlight, lightning, or heat escaping Earth’s crust
may have supplied the energy for spontaneous
chemical reactions
 Beginning of life
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Organic molecules; pre-cells, e.g., nanobes
Proteins, lipids, carbohydrates, and nucleic acids
Perhaps RNA preceded DNA
Self-replication was a necessity
Animation: Miller's reaction chamber
experiment
Is This a 3.5 Billion-Year-Old Fossil?
There Are Several Hypotheses about
How Life Began on Earth