Chapter 10: Chapter 10: Principles of EvolutionPrinciples of Evolution

What is What is EvolutionEvolution??

• Evolution is the process of biological change by which descendants come to differ from their ancestors– It is the central theme in all fields of Biology

Carolus LinnaeusCarolus Linnaeus

• Developed a classification system for all types of organisms – Organisms were grouped by

similarities but also reflected evolutionary relationships

Georges Louis Leclerc de BuffonGeorges Louis Leclerc de Buffon

• Proposed that species shared ancestors instead of arising separately

• Suggested that Earth was much older than 6,000 years old which was the common belief at the time

Erasmus DarwinErasmus Darwin

• Charles Darwin’s grandfather

• Proposed that all living things were descended from a common ancestor and that more-complex forms of life arose from less-complex forms

Early misconception by Jean-Early misconception by Jean-Baptiste Lamarck (1809)Baptiste Lamarck (1809)

• Proposed all organisms evolved toward perfection and complexity

• Use and Disuse of Organs Theory—organisms respond to their environment by developing new structures as needed– The more an organ was in use, the bigger it would

become and vice versa

• Inheritance of Acquired Traits—these traits are passed on to offspring– Ex. giraffes

Lamarck continued…Lamarck continued…

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Lamarck cont.Lamarck cont.• In order for groups of organisms to have

adapted over time, populations must have evolved rather than individuals.

Charles Darwin (1809-1882)Charles Darwin (1809-1882)

• An English scientist who formed ideas that are now the basis of modern evolutionary theory

• When he was 21, Darwin took an apprenticeship on a 5-year scientific voyage on the HMS Beagle– He was the unofficial naturalist on the ship

collecting many specimens along the way

Darwin’s voyage (Page 277)Darwin’s voyage (Page 277)

• The Galapagos Islands, off the coast of Ecuador, became the focal point in Darwin’s observations

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• In 1859, Darwin published his theories and ideas in the book On the Origin of Species by Natural Selection

• Variation is the difference in the physical traits of an individual from those of other individuals in the group to which it belongs– Can occur either among members of

different species (interspecific) or same species (intraspecific)

• Darwin believed that variation arose when species adapted to their surroundings. – An adaptation is a feature that allows an

organism to better survive in its environment• An adaptation can lead to genetic change in a

population over time

Artificial selectionArtificial selection• Darwin also conducted

many breeding experiments with pigeons and found that organisms with specific traits could be crossed to result in offspring that had those selected traits; this is called artificial selection

Humans are the selecting agent in artificial selection

In order for—artificial or natural—selection to occur, the trait must be heritable. Heritability is the ability of a trait to be

passed down from one generation to the next

Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. The environment (nature) is the selective

agent

Four main principles to the theory of natural Four main principles to the theory of natural selectionselection

• Variation – Individuals in a population have varying

characteristics

• Overproduction – Organisms tend to produce more offspring than can

survive to maturity

• Adaptation – The traits of survivors will become more common in a

population

• Descent with modification– Surviving individuals tend to reproduce more than

others

Overview of the Evolution TheoryOverview of the Evolution Theory

1. Variation exists within the genes of every population or species (as a result of random mutation)

2. In a particular environment, some individuals of a population or species are better suited to survive (a result of variation) and have more offspring (natural selection)

Overview cont.Overview cont.

3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population

4. There is a clear proof from fossils and many other sources that living species evolved from organisms that are extinct.

• Natural selection acts on phenotypes or physical traits, rather than on genetic material itself.

Evidence for EvolutionEvidence for Evolution

• Fossil Record

• Geography

• Embryology

• Body Structures (Anatomy)

• Biochemistry (Genes and Proteins)

Fossil RecordFossil Record

• Fossils of animals show a pattern of development from early ancestors to their modern descendants

• “Intermediate” (missing links) species show how organisms evolved new adaptations

• Fossil Evidence Examples

Problems with fossilsProblems with fossils

• It is difficult to find fossils of soft-bodied organisms with no hard parts that can be left behind

• Organisms decay at different rates and may not leave any traces

GeographyGeography• Shows similarities among species living on

different areas

• “Descent with

modification”

EmbryologyEmbryology

• Most embryos look very similar and have gill slits and tails.

• This suggests a common ancestor.

AnatomyAnatomy

• Comparing structures of related organisms to find relationships between organisms

• Ex. Homologous Structures– Comparing Primate Skeletons

• Comparing common structures between unrelated organisms to find how natural selection affects organisms in similar environments

• Ex. Analogous Structures

Homologous StructuresHomologous Structures

• Have a common evolutionary origin

• Similar structure but different functions

Analogous StructuresAnalogous Structures

• Structures that are similar in function but do not have a common evolutionary origin

• Different structures but similar functions– Ex. Bird wing and an insect wing

• Shows that different species evolved similar traits to overcome similar selective agents

Homologous structures versus Homologous structures versus Analogous structuresAnalogous structures

Vestigial StructuresVestigial Structures

• A body structure that has no function presently but was probably useful to an ancestor

• Even though the species does not need the feature, the structure is still passed on to offspring– Ex. Eyes on blind mole-rats, flightless wings

on an ostrich, appendix/tonsils on humans

BiochemistryBiochemistry• As organisms evolve, the differences in

the amino acids, DNA, and proteins they make should change gradually

• The more amino acid differences there are between two organisms, the more distantly related they are