How Populations Evolve CHAPTER 13 Darwin's Voyage and Origin of Species Lamarck's and Lyell's Contributions Descent with Modification Evidence of Evolution

How Populations EvolveCHAPTER 13How Populations EvolveCHAPTER 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















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

An Early Proposal of Evolution: Theory of Acquired Characteristics

Charles LyellIn Principles of Geology, 1830

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

• The earth must be much older than 6,000 (according to Biblical interpretations of human generations since Adam and Eve)

Earth Process Are Constant and Have Been Going On For Billions of Years

The earth is now considered to be about 4.6

billion years old

Figure 13.4

The Voyage of the Beagle

Figure 13.5

• Darwin was intrigued by he fact that Galápagos Island organisms resembled those in South America.


• 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.















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

Figure 13.10

Related Animals Descended From a Common Ancestor

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

Figure 13.11

Homologous Structures Are Derived From the Same Parts

of a Common Ancestor

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 Ancestryand 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















Natural Selection

• Darwin’s finches

– Are an excellent example of natural selection and adaptive evolution.

Examples of Artificial Selection

Varieties of maize (corn)

Varieties of chili peppersDog breeds

New species from wild mustard

• 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.

Observations That Led Darwin to the Theory of Natural Selection

• Differential reproductive success

– Those individuals with traits best suited for the local environment leave more fertile offspring.

– Successful variations become more common

Population with varied inherited traits

Elimination of individuals with certain traits

Reproduction of survivors

Modification: Increased frequency of traits that enhance survival and reproductive success

• 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”

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 formsunder incomplete antibiotic treatment (selection)

2. The few surviving resistant cells divide and repopulate with

all resistant offspring















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.

• 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 Characteristics of Populations

Genetic Variation from Sexual Recombination

Figure 13.19

Polymorphism in Color and Pattern of Garter Snakes
















• 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















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















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.

Figure 13.28

Three Types of Natural Selection

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.















Documents

How Populations Evolve CHAPTER 13 Darwin's Voyage and Origin of Species Lamarck's and Lyell's Contributions Descent with Modification Evidence of Evolution