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…
http://www.princessleia.com/images/MyImages/essays/giraffe_lamark.jpg
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
Dar
win
's jo
urne
y
• 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