Transcript a17 HowPopEvolve

How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
Charles Darwin and The Origin of Species
• Charles Darwin’s On the Origin of Species by Means of
Natural Selection
– Was published on November 24, 1859.
• Darwin argued that contemporary species arose from
ancestors
– Through a process of “descent with modification,” with
natural selection as the mechanism.
• The basic idea of natural selection is that
– Organisms can change over generations.
– Individuals with certain heritable traits leave more
offspring than others.
• The result of natural selection is evolutionary
adaptation.
Seahorse Camouflage
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
An Early Proposal of Evolution: Theory of Acquired Characteristics
Jean Baptiste Lamarck (~ 1800) : Theory of Acquired Characteristics
• Use and disuse alter shape and form in an animal
• Changes wrought by use and disuse are heritable
• Explained how a horse-like animal evolved into a giraffe
Earth Process Are Constant and Have Been Going On For Billions of Years
Lyell’s Gradualism or Uniformitarianism
• The laws have science have not changed over time
• Natural geological processes occurring today are
the same ones that operated in the past
• Natural process effect the earth gradually over long
periods of time
Charles Lyell
In Principles of
Geology, 1830
• The earth must be much older than 6,000
(according to Biblical interpretations of human
generations since Adam and Eve)
The earth is now
considered to be about 4.6
billion years old
The Voyage of the Beagle
Figure 13.4
•
Darwin was intrigued by he fact that Galápagos Island organisms
resembled those in South America.
Figure 13.5
Descent with Modification
•
Darwin made two main points in The Origin of Species:
–
Organisms inhabiting Earth today descended from ancestral
species.
–
Natural selection was the mechanism for descent with
modification.
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
Evidence of Evolution
• Biological evolution has left observable marks.
1. Fossils
– Are preserved remnants or impressions left by organisms
that lived in the past.
– Are often found in sedimentary rocks.
Progression of Modification Through Time Seen in Fossil Remains
Primitive horse foot
reconstructions from fossils
Biogeography
2. Biogeography
– The of the geographic distribution of species.
– First suggested to Darwin that today’s organisms
evolved from ancestral forms.
– Organisms that are related to each other in
structure and appearance tend to occur in the
same geographical area
– Organisms that are more distantly related tend to
be found in distant geographical areas
Related Animals Descended From a Common Ancestor
Figure 13.10
Comparative Anatomy
3. Comparative anatomy
– Is the comparison of body structure between
different species.
– Confirms that evolution is a remodeling process.
– Homology
• Is the similarity in structures due to common
ancestry.
• The more recently two species diverged from one
another, the more similar their homologous
structures
Homologous Structures Are Derived From the Same Parts
of a Common Ancestor
Figure 13.11
Dolphins and Whales are Related to Land Mammals By Homologous Pelvis and Feet
Comparative Embryology
4. Comparative embryology
– Organisms with common ancestors share certain
developmental structures as they grow into adults
– One would expect unrelated organisms to share
little similarity in embryological growth
Comparative Embryology Suggests Common Ancestry
and Modification By Descent
Molecular Biology
5. Evolutionary
relatedness can be
discerned through
molecular
comparisons
• Compare genes and
proteins of different
organisms
• Only 5% difference in
DNA sequences between
humans and chimpanzees
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
Natural Selection
• Darwin’s finches
– Are an excellent example of natural selection and
adaptive evolution.
Examples of Artificial Selection
Varieties of maize (corn)
New species from wild mustard
Varieties of chili peppers
Dog breeds
Observations That Led Darwin to the Theory of Natural Selection
•
•
•
•
Overproduction
–
All species tend to produce excessive
numbers.
–
This leads to a struggle for existence.
Individual variation
–
Variation exists among individuals in a
population.
–
Much of this variation is heritable.
Competition
–
Struggle to get food, mates, shelter, escape
from predators
–
Some variations are more successful than
others and those organisms with those
variations are the “fittest”
Population with varied inherited traits
Elimination of individuals with certain traits
Reproduction of survivors
Differential reproductive success
–
–
Those individuals with traits best suited for the
local environment leave more fertile offspring.
Modification: Increased frequency of traits that
Successful variations become more common enhance survival and reproductive success
Natural Selection in Action
• Examples of natural selection include
– Pesticide resistance in insects.
– Drug-resistant strains of HIV.
– The development of antibiotic-resistant bacteria.
1. Selection of resistant forms
under incomplete antibiotic
treatment (selection)
2. The few surviving resistant
cells divide and repopulate with
all resistant offspring
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
The Modern Synthesis:
Darwinism Meets Genetics
• The modern synthesis is the fusion of genetics with
evolutionary biology.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Populations as the Units of Evolution
•
A population
–
Is a group of individuals of the same species living in the same place
at the same time.
–
Is the smallest biological unit that can evolve.
Genetic Characteristics of Populations
• Population genetics
– Focuses on populations as the evolutionary units.
– Tracks the genetic makeup of populations over time.
• Individual variation abounds in populations.
– Not all of this variation is heritable.
– Only the genetic component of variation is relevant to
natural selection.
• A population is said to be polymorphic for a characteristic
if two or more morphs, or forms, are present in noticeable
numbers.
Genetic Variation from Sexual Recombination
Polymorphism in Color and Pattern of Garter Snakes
Figure 13.19
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
Sources of Genetic Variation
• Mutations and sexual recombination
– Produce genetic variation.
– Mutations
• Are changes in the DNA of an organism.
– Sexual recombination
• Shuffles alleles during meiosis.
Analyzing Gene Pools
• The gene pool
– Consists of all
alleles of all
individuals making
up a population
– Gene occurance
usually expressed
as a gene
frequency
(percentage of
occurrence in
population)
Mechanisms of Microevolution
Microevolution is defined as
–
•
A generation-to-generation change in a
population’s frequencies of alleles.
The main causes of microevolution are
1. Genetic drift
2. Gene flow
3. Mutations
4. Natural selection
Causes of Evolutionary Change
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
1. Genetic Drift
• Genetic drift
– Is a change in the gene pool of a small population
due to chance.
• Two categories of genetic drift
– Bottleneck Effect
• Death of most of population leaves only a few
survivors and their genes to rebuilt the population
– Founder Effect
• Small group randomly removed from a larger
population begins a new colony
Genetic Drift: The Bottleneck Effect
•
The bottleneck effect
–
Is an example of genetic drift.
–
Results from a drastic reduction in population size.
–
Bottlenecking in a population usually reduces genetic variation.
Genetic Drift: The Founder Effect
•
The Founder effect
–
Is genetic drift in a new colony
–
Can lead to a high incidence of genetic disease in a colony population
By chance, 7 q
alleles and 3 Q
alleles are
carried by this
subgroup
2. Gene Flow
• Gene flow
– Is genetic
exchange with
another
population.
– Tends to reduce
genetic
differences
between
populations.
Asian/Latino/Black/Caucasian/
Native American
3. Mutation
• Mutations
– Are changes in an organism’s DNA.
– Alone do not have much effect on a large
population.
– Can have significant cumulative effects on a
population.
– Produces new gene forms
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection
4. Natural Selection
• Of all causes of microevolution, only natural selection
promotes adaptation.
• Three results of natural selection
• Directional selection
– Shifts the phenotypic “curve” of a population.
– Selects in favor of some extreme phenotype.
• Disruptive selection
– Can lead to a balance between two or more
contrasting morphs in a population.
• Stabilizing selection
– Maintains variation for a particular trait within a
narrow range.
Three Types of Natural Selection
Figure 13.28
Biology and Society: Persistent Pests
• Mosquitoes and
malaria
– In the 1960s, the
World Health
Organization
(WHO) began a
campaign to
eradicate the
mosquitoes that
transmit malaria.
– It used DDT, to
which some
mosquitoes have
evolved
resistance.
How Populations Evolve
CHAPTER 13
• Darwin's Voyage and Origin of Species
 Lamarck's and Lyell's Contributions
 Descent with Modification
• Evidence of Evolution
•
Fossils, Biogeography, Comparative Anatomy, Comparative Embryology, & Molecular Biology
• The Theory of Natural Selection
•
Artificial Selection: A Model for Natural Selection
•
Overproduction, Variation, Competition, and Differential Reproduction
• Modern Synthesis: Darwin and Genetics
 Populations are Evolutionary Units
 Sources of Genetic Variation
 Gene Pools and Evolution
• Mechanisms of Evolution
 Genetic Drift, Gene Flow, Mutation, and Natural Selection