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Evolution
Chapter 15
Outline
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
An Introduction to Evolution
A Brief Overview of the Early Development of
Evolutionary Concepts

Charles Darwin

Evidence for Evolution

Microevolution – Evolution within Species

Rates of Evolution

Macroevolution – How Species Evolve

The Role of Hybridization in Evolution
An Introduction to Evolution

Natural selection - tendency of organisms with
favorable adaptations to their environment to
survive and produce new generations
• Theory proposed by Charles Darwin, 1859, On the
Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life.

Organic evolution - accumulation of genetic
changes in populations of living organisms through
many changes
An Introduction to Evolution
The Study of Evolutionary Biology
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Subdisciplines of evolutionary biology:
• Behavioral evolution - study of development of
behavioral traits
− Mating, food gathering, social interactions,
predatory-prey relationships
• Evolutionary developmental biology - study of effect
of genetic variation on traits that effect survival and
reproduction
• Evolutionary ecology - study of how ecological
features (i.e., life histories and reproductive strategies)
effect evolution of species and ecosystems
An Introduction to Evolution
The Study of Evolutionary Biology

Subdisciplines of evolutionary biology cont’d.:
• Evolutionary genetics - use of molecular and
transmission genetics to understand origins of genetic
variability
• Evolutionary paleontology - use of fossil record to
examine large-scale evolutionary change, including
origins of lineages and changes in anatomy over time
• Evolutionary physiology and morphology - study of
adaptation through biochemical, physiological, and
anatomical changes
An Introduction to Evolution
The Study of Evolutionary Biology

Subdisciplines of evolutionary biology cont’d.:
• Human evolution - use of all disciplines of evolution to
study genetic variation in both modern and historical
human populations
• Molecular evolution - study of evolutionary changes
in DNA in relation to gene structure, organization, and
control of expression
• Systematics - naming of species and determination of
their evolutionary relationships
An Introduction to Evolution
Evolution in Agriculture

Humans use artificial selection, or breeding, to
change agricultural and domestic plants and
animals
• Evolution directed by humans

Agricultural systems agents of change by
influencing evolution of native species
• Example: insect populations evolving resistance to
insecticides
An Introduction to Evolution
Evolutionary Medicine

Evolutionary medicine applies evolutionary
principles to way in which we treat illness
• Example: evolution of bacteria, obtaining genetic ability
to overcome antibiotics

Also applies application of evolutionary research
involving discovery of natural compounds that may
be useful in medicine
• Can predict where to look for new products in relatives
of useful plants
• Can look for plants that might have undergone
selection pressure for those adaptations
An Introduction to Evolution
Species Extinctions and Invasions
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
Loss of species undermines
health of entire ecosystems
Conservation biology uses
evolutionary principles to
understand species expansion or
contraction in response to
changing environments
Kudzu, and invasive plant from Japan

Evolutionary biologists study species invasions
• Natural selection in introduced plants, where there are
no natural pests or herbivores, favors reproduction
– Outcompete native vegetation
An Introduction to Evolution
Biotechnology and Evolution

Evolutionary biologists determine fate of
transgenes after genetically engineered crop plants
planted in fields
• Transgenes - foreign genes introduced into plants
through genetic engineering
• Gene exchange between crop plants and their wild
relatives?
− Herbicide resistant weeds
A Brief Overview of the Early
Development of Evolutionary Concepts

Aristotle (384-322 BC) - arranged organisms from
simplest to most complex = scale of nature
• Implied organisms static and do not evolve


Leonardo da Vinci (1452-1519) - observed fossils
part of previously existing organisms now extinct
Count de Buffon (1707-1788) - described all
known plants and animals
• Presented evidence that organisms change across
generations
A Brief Overview of the Early
Development of Evolutionary Concepts

End of 18th century many prominent biologists
believed hereditary changes in populations over
long periods of time occurred as result of
inheritance of acquired characteristics
• Jean Baptiste Lamarck (1744–1829) - characters
acquired during life passed on and became cumulative

Major revolutions in evolutionary thought
occurred in last 150 years
A Brief Overview of the Early
Development of Evolutionary Concepts



First revolution - Charles Darwin, Origin of Species, 1859
• Evolution by natural selection
Second revolution - 1930’s
• Theories of Darwinian natural selection, Mendelian
genetics and population genetics intersected providing
better understanding of mechanisms of evolution
Third revolution - Now
• Evolution of development = “Evo-devo”
− Homeobox genes - regulatory genes that act as
developmental switches
Charles Darwin
(1809–1882)
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Assistant naturalist on HMS Beagle to voyage around
world and chart coastlines, 1831–1836
• Read Charles Lyell’s geology book, theorized earth
much older than previously believed
• Collected plants and animals in South America,
Galapagos Islands, Australia and New Zealand
Guided by ideas of Malthus, 1798
• Populations grow geometrically until food supplies and
other factors limit growth
Presented joint paper on natural selection with Alfred
Wallace year prior to publication of Origin of Species
Evidence for Evolution

Homology - characteristic shared by different organisms
with common ancestry
• Convergent evolution similarities not due to
common ancestry
− Plants of different
ancestry adapted in
similar ways to common
environmental conditions
in different parts of world
Cactus and Euphorbia
Evidence for Evolution

Structure and relationships of proteins, DNA, and
other molecules; and common use of ATP
• Ex.: cytochrome c oxidase - universal in all living
organisms
− Suggests early, single origin


Fossil Record
Geographical
distribution of
organisms
Fossil
fern
Microevolution – Evolution Within Species
Natural Selection



Darwin observed:
• Artificial selection - changes in populations of domestic
animals by retaining animals with desirable traits
• Limited supply of food and other resources prevents
some individuals from reproducing
• Competitive abilities of individuals vary within
populations
• Comparative anatomy and embryology
Reasoned individuals best adapted to utilize available
resources would increase in # in succeeding generations
Natural selection - descent with modification
Microevolution – Evolution Within Species
Natural Selection

Darwin based natural selection on:
– Overproduction of offspring
– Struggle for existence - competition for resources
– Inheritance and accumulation of favorable variations
– Survival and reproduction of fittest (differential survival
and reproduction)

Criticism of natural selection in Darwin’s time:
natural selection did not explain origin of
hereditary variation
Microevolution – Evolution Within Species

Mutation - change in gene or chromosome
• Deletion - part of chromosome breaks off
• Translocation - piece of chromosome becomes
attached to another
• Inversion - part of chromosome breaks off and
reattaches in inverted position
• One or more nucleotide pairs changes
• Most mutations harmful; some silent or some produce
characteristic that helps organism survive change
A. Deletion
B. Translocation
C. Inversion
Microevolution – Evolution Within Species

Migration - gene flow between populations when
individuals or gametes migrate from one
population to another
• Depends on size of population and extent of isolation

Genetic drift - changes in genetic make-up of
population due to random events
Rates of Evolution


Darwin believed evolution by natural selection
slow and gradual
Contemporary biologists believe theory of
punctuated equilibrium
• Major changes occurred in spurts (ca. 100,000 years)
followed by millions of years with minor change
• Hypothesis based on fossils - reveal large gaps in fossil
record
Macroevolution – How Species Evolve


Geographic isolation
• Isolation of two populations prevents gene flow
• Random mutations spread only throughout population
in which they arise
• Genetic changes become so great gene flow between
populations no longer occur
Ecological isolation
• Ecological factors such as climate or soils play role in
isolation, as do time and mechanical isolating factors
• Results in sympatric species that occupy overlapping
ranges of territories, and do not exchange genes
Macroevolution – How Species Evolve
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Mechanical isolation
• Ex.: pollinia of orchids
Other isolating mechanisms:
• Sperm chemically or mechanically prevented from
reaching egg
• Postzygotic isolating mechanisms:
− Failure of embryos to develop
− Failure of hybrids to survive or breed
Chromosomes may not pair normally at meiosis,
resulting in sterile hybrids
The Role of Hybridization in Evolution

Hybrids - offspring produced by parents differing in
one or more characteristics
• May have gene combinations better suited to
new environments
• Two related species may hybridize
−Introgression - intercrossing between hybrids
and parents
The Role of Hybridization in Evolution
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
Polyploidy - occurrence of double normal chromosome #
• Result of failure of meiosis to halve chromosome # in
gametes
• Polyploids produced when these gametes participate in
fertilization
Hybrids often sterile because chromosomes do not pair
properly at meiosis
• If polyploid formed in hybrid, then chromosomes can
pair and overcome sterility
• >50% of flowering plant species originated this way
The Role of Hybridization in Evolution

Sterile hybrids may reproduce asexually
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Apomixis - production of seeds without fertilization
• Combination of apomixis and sexual reproduction may
be highly successful
− Dandelions
Dandelion
Review


An Introduction to Evolution
A Brief Overview of the Early Development of
Evolutionary Concepts

Charles Darwin

Evidence for Evolution

Microevolution – Evolution within Species

Rates of Evolution

Macroevolution – How Species Evolve

The Role of Hybridization in Evolution