1. Ch.10: Principles of Evolution

2. Section 3: Theory of Natural Selection

3. Artificial Selection
Natural variation exists in all populations & some variation is heritable, meaning it can be passed from one generation to the next
For 100s of years, humans have been using artificial selection - the process by which humans change a species by breeding it for certain traits
Darwin believed that a process similar to artificial selection could happen in nature

4. Darwin Publishes his Theory
Over 20 years after Darwin’s voyage on the Beagle, he received a short essay from Alfred Russel Wallace that summarized all of Darwin’s thoughts about evolution.
This prompted Darwin to publish his own book called On the Origin of Species by Means of Natural Selection.
Natural Selection is the mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals

5. 4 Main Principles of Natural Selection
1.Variation - natural genetic variation exists in all populations
Population is all the individuals of a species that live in an area
2.Overproduction - populations tend to produce more offspring than the environment can sustain, leading to competition for resources

6. 3.Adaptation - some variations allow an individual to better survive & reproduce
Fitness is a measure of the ability to survive and produce more offspring relative to other members of the population
4.Descent with modification - Over time, natural selection results in changes in a population, as only those with the highest fitness will pass on their genes

7. Natural Selection acts on Phenotypes
Natural selection doesn’t create new alleles, genetic mutations do
Natural selection can only act on traits that already exist in a population
As an environment changes, different traits become beneficial

8. Section 4: Evidence of Evolution

9. Darwin’s Evidence
The most important & convincing evidence of evolution comes from fossils, geography, embryology, & anatomy
Fossils - fossil organisms in lower, older layers of rock are more primitive than those in upper, newer layers; this supports descent with modification

10. Geography - Darwin observed that certain plants & animals in the Galapagos Islands were similar but not identical to mainland species
He hypothesized that some individuals from the mainland migrated to the islands & then adapted to each particular island
biogeography is the study of the distribution of organisms around the world

11. Embryology - similar features of embryos in very different organisms suggests evolution from a distant common ancestor
Ex. vertebrate embryos all have gill slits as embryos, but not as adults

12. Anatomy - comparing body parts of different species provides evidence of evolution
Homologous structures are features that are similar in structure but appear in different organisms & have different functions (suggest a common ancestor)
Analogous structures are structures that perform a similar function but are not similar in origin; they arise due to similar environmental challenges, not common ancestry

13. Structural Patterns & Evolutionary History
Structural patterns are clues to the history of a species
Vestigial structures are remnants of organs or structures that had a function in an early ancestor, but serve little or no function in the present
Ex. pelvic bones & hind limb bones in snakes
Ex. appendix & tail bone in humans

14. Section 5: Evolutionary Biology Today

15. Fossil Record
Paleontology (the study of fossils or extinct organisms) was a new science in Darwin’s time
Our fossil record is incomplete, but it does support the theory of evolution
Many transitional fossils have been found that show the change in organisms over time

16. Molecular & Genetic Evidence
DNA Sequence Analysis - The more related two organisms are, the more similar their DNA will be.
Pseudogenes - Like vestigial structures, pseudogenes no longer function but are still carried along with functional DNA. Similarities between pseudogenes suggest a common ancestor

17. Homeobox Genes - control the development of specific structures; found in many organisms & indicate a very distant common ancestor
Protein Comparisons - Molecular fingerprinting compares similarities among proteins of organisms. Species that have the same proteins most likely come from a common ancestor

18. Evolution Unites all Fields of Biology
All biological fields contribute to evolutionary theory
The theory of natural selection along with genetics is sometimes called the modern synthesis of evolutionary theory
The basic principles of evolution are used in many scientific fields such as medicine, geology, geography, chemistry