Chapter 13

The Theory of Evolution

Section 1: The Theory of Evolution by Natural Selection

Section 2: Evidence of Evolution

Section 3: Examples of Evolution

Section 1

The Theory of Evolution by Natural Selection

Objectives:•Identify several observations that led Darwin to conclude that species evolve.•Relate the process of natural selection to its outcome.•Summarize the main points of Darwin's theory of evolution by natural selection as it is stated today.•Contrast the gradualism and punctuated equilibrium models of evolution.

Section 1

The Theory of Evolution by Natural Selection

Darwin Proposed a Mechanism for Evolution

•Science Before Darwin’s Voyage Lamarck proposed an incorrect mechanism for how organisms evolve, but he correctly pointed out that change in species is linked to an organism’s environment.•Darwin’s Observations Charles Darwin concluded that animals on the coast of South America that resembled those on the nearby islands evolved differences or descended with modification after separating from a common ancestor.

Section 1

The Theory of Evolution by Natural Selection

Darwin Proposed a Mechanism for Evolution continued

•Growth of Populations Darwin was influenced by Thomas Malthus, who wrote that populations tend to grow as much as the environment allows.

Section 1

The Theory of Evolution by Natural Selection

Evolution by Natural Selection•Natural Selection Natural selection is differential reproductive success and natural selection leads to adaptations in a population.•Publication of Darwin’s Work Darwin and Wallace independently came up with a mechanism for evolution, natural selection, and this prompted Darwin to publish his work.•Darwin’s Theory Darwin proposed that natural selection favors individuals that are best able to survive and reproduce and this causes populations to evolve.

Section 1

The Theory of Evolution by Natural Selection

Darwin’s Ideas Updated•Change Within Populations Natural selection causes the frequency of certain alleles in a population to change over time.•Species Formation Under certain conditions, change within a species due to reproductive isolation can lead to new species.•The Tempo of Evolution Gradualism is a process of evolution in which speciation occurs gradually, and punctuated equilibrium is a process in which speciation occurs rapidly between periods of little or no change.

Section 2

Evidence of Evolution

Objectives:•Describe how the fossil record supports evolution.•Summarize how biological molecules such as proteins and DNA are used as evidence of evolution.•Infer how comparing the anatomy and development of living species provides evidence of evolution.

Section 2

Evidence of Evolution

The Fossil Record•Formation of Fossils Evidence of orderly change can be seen when fossils are arranged according to their age.

Section 2

Evidence of Evolution

Anatomy and Development•Vestigial Structures Reduced or nonfunctional vestigial structures, such as hind limbs in whales, provide evidence of an organism’s evolutionary history. •Homologous Structures Homologous structures, structures in different organism that indicate a shared ancestry, include the vertebrate forelimb.

Section 2

Evidence of Evolution

Biological Molecules•Proteins Differences in amino acid sequences are greater between species that are more distantly related than between species that are more closely related.•Nucleic Acids Differences in DNA sequences are greater between species that are more distantly related than between species that are more closely related.

Section 3

Examples of Evolution

Objectives:•Identify four elements in the process of natural selection.•Describe how natural selection has affected the bacteria that cause tuberculosis.•Relate natural selection to the beak size of finches.•Summarize the process of species formation.

Section 3

Examples of EvolutionNatural Selection at Work•Factors in Natural Selection Individuals that have traits that enable them to survive in a given environment can reproduce and pass those traits to their offspring. •Evolution of Antibiotic Resistance Experiments show that evolution through natural selection has occurred within populations of antibiotic-resistant bacteria, such as the bacteria that cause tuberculosis.•Evolution in Darwin’s Finches Experiments show that evolution through natural selection has occurred in beak size in Darwin’s Finches.

Section 3

Examples of EvolutionFormation of New Species•Speciation Speciation begins as a population adapts to its environment. •Forming Subspecies Populations of the same species that differ genetically because of adaptations to different living conditions are called subspecies. Newly formed subspecies are on the road towards speciation.•Maintaining New Species Reproductive isolation through reproductive barriers keeps species from breeding with one another.