Chapter 8 Evolution and Natural Selection

What happens when the environment changes?

If the environment changes, the alleles causing the traits favored by natural selection may change too.

Disruptive Selection

In which individuals with extreme phenotypes experience the highest fitness, and those with intermediate phenotypes have the lowest.

Directional Selection

Individuals with one extreme of the range of variation in the population have higher fitness.

Condition 3: Differential reproductive success

Individuals with the version of the trait most suited to reproduction in their environment generally leave more offspring than individuals with other versions of the trait.

Condition 3: Differential reproductive success

More organisms are born than can survive Organisms are continually struggling for existence Some organisms are more likely to win this struggle and survive and reproduce.

What is the ultimate source of all genetic variation?

Mutation

What is the only way that new alleles can be created within a population?

Mutation is the only way that new alleles can be created within a population, and thus it generates the variation on which natural selection can act.

What can mutations be caused by?

Mutations can be caused by high-energy radiation or chemicals in the environment, and also can appear spontaneously.

What can natural selection be thought as?

Natural selection can also be thought of as the elimination of alleles that reduce the reproductive rate of individuals carrying those alleles, relative to the reproductive rate of individuals who do not.

How does Natural Selection cause the evolution of complex traits and behaviors?

Natural selection can change allele frequencies for genes involving complex physiological processes and behaviors. Sometimes a trait that has been selected for one function is later modified to serve a completely different function.

Are evolution and natural selection the same thing?

No! Evolution and Natural Selection are not the same thing.

Fixation

Occurs when an allele's frequency in a population reaches 100% (and the frequency of all other alleles of that genes becomes 0%).

Stabilizing Selection

Occurs when individuals with intermediate phenotypes are the most fit.

Adaptation

Process by which organisms become better matched to their environment and to the specific features that make an organism more fit, occurs as a result of natural selection.

Genetic Similarities

The longer two species have been evolving on their own, the greater number of genetic frequencies.

Homologous Structures

The similarities in the bone structure of the forelimbs of mammals demonstrate common ancestry.

Condition 2: Heritability

The transmission of traits from parents to their children through genetic information

Inheritance or heritability

The transmission of traits from parents to their children through genetic information.

What happens when such an alteration changes an allele in an individual's gamete-producing cells?

This constitutes evolution within the population.

Condition 1: Variation for a trait

Variation is all around us. Variation is the raw material for evolution

Molecular Biology

examination of life at the level of individual molecules.

Comparative anatomy and embryology

growth, development, and body structures of major groups of organisms.

Laboratory and field studies

implementation of the scientific method to observe and study evolutionary mechanisms.

Convergent Evolution

may act on different starting materials (such as a flipper or forelimb) and modify them until they serve similar purposes.

Biogeography

patterns in the geographic distribution of living organisms.

Fossil Record

physical evidence of organisms that lived in the past.

Bottleneck

population that is quickly reduced to a small fraction to its original size.

THREE important elements to an organism's fitness

1. An individual's fitness is measured relative to the other genotypes or phenotypes in the population. 2. Fitness depends on the specific environment in which the organism lives. 3. Fitness depends on an organism's reproductive success compared with other organisms in the population.

What are the ways in which natural selection can change populations?

1. Directional Selection 2. Stabilizing Selection 3. Disruptive Selection

What are the factors that prevent populations from progressing inevitably toward perfection?

1. Environment changes quickly. Environments can change more quickly than natural selection can adapt organisms. 2. Variation is needed as the raw material of selection. Mutation does not produced all possible alleles. 3. There may be different alleles for a trait, each causing equal fitness. There is not always a single optimum adaptation for an environment.

What are the FIVE primary lines of evidence in the Theory of Evolution?

1. Fossil Record 2. Biogeography 3. Comparative anatomy and embryology 4. Molecular Biology 5. Laboratory and field studies

What are the four different mechanisms evolution can occur by?

1. Mutation 2. Genetic Drift 3. Migration 4. Natural Selection

evolution

A change in allele frequencies within a population. A genetic change in the population. Heritable change in a line of descent.

Laboratory and Field Experiments

A fifth line of evidence for the occurrence of evolution comes from multigeneration experiments and observations.

Fitness

A measure of the relative amount reproduction of an individual with a particular phenotype. The alleles carried by an individual with high fitness will increase in a population over time.

Natural Selection

A mechanism of evolution that occurs when there is heritable variation for a trait, and individuals with one version of the trait have greater reproductive success than do individuals with a different version of the trait.

genetic drift

A random change in allele frequencies in a population.

Founder effect

A small number of individuals may leave a population and become the founding members of a new, isolated population.

What does molecular biology reveal?

All living organisms share the same genetic code. DNA similarities and differences. Related vs. unrelated individuals -Compare DNA sequences for individual genes. The more distantly you and another individual are related, the more your DNA differs.

What does replicated, controlled laboratory selection experiments and long-term field studies of natural populations allow us to do?

Allow us to watch and measure evolution as it occurs.

Migration

Also called gene flow, leads to a change in allele frequencies in a population as individuals move into or out of the population.

mutation

An alteration of the base-pair sequence of an individual's DNA, and when this alteration occurs in the DNA that codes for a particular gene, the change in the DNA sequence may change that allele.

Vestigal Structures

At the extreme, homologous structures sometimes come to have little or no function at all.

Who developed the theory of evolution?

Charles Darwin developed the theory of evolution.

What are the THREE conditions necessary for natural selection to occur?

Condition 1: Variation for a trait Condition 2: Heritability Condition 3: Differential reproductive success

What is genetic drift a significant agent of?

Genetic drift is a significant agent of evolutionary change, primarily in small populations.