1. Evolution
Glencoe Chapter 15

2. Darwin’s Theory of Natural Selection
Charles Darwin

3. Darwin’s Theory of Natural Selection
HMS Beagle

4. Darwin’s Theory of Natural Selection
Galapagos Islands
Each island had different variety of animals
Finches on islands resembled animals on South American mainland but were not the same species
Darwin suspected that populations from mainland changed after reaching the islands
Hypothesis: new species occur through small changes in ancestral species

5. Darwin’s Theory of Natural Selection
Artificial selection-changes in species due to human intervention, breeding to produce desirable traits
Darwin-four basic principles
Individuals in a population show variation
Variations can be inherited, passed down from parent to offspring
Organisms have more offspring than can survive on available resources
Variations that increase reproductive success will have a greater chance of being passed on than those that do not increase reproductive success
Natural selection

6. Darwin’s Theory of Natural Selection
Principles of natural selection
Principle
Example
Individuals in a population show variations among others of the same species.
The students in a classroom all look different.
Variations are inherited.
You look similar to your parents.
Animals have more young that can survive on the available resources.
The average cardinal lays nine eggs per summer. If each cardinal lived only one year, in seven years there would be a million offspring if all survived.
Variations that increase reproductive success will be more common in the next generation.
If having a fan-shaped tail increases reproductive success of pigeons, then more pigeons in the next generation will have fan-shaped tails.

7. Darwin’s Theory of Natural Selection
Darwin-The Origin of Species
Evolution: cumulative changes in groups of organisms through time

8. Evidence of Evolution
Fossils-provide record of species that lived long ago
Derived trait-newly evolved features
feathers
Ancestral trait-more primitive features that do appear in ancestral forms
Teeth

9. Evidence of Evolution Comparative anatomy
Homologous structures-anatomically similar structures inherited from a common ancestor

10. Evidence for Evolution
Vestigial structures-reduced forms of functional structures in other organisms
Human appendix, snake pelvis

11. Evidence for Evolution
Analogous structure-used for the same purpose and superficially similar in construction, but not inherited from a common ancestor

12. Evidence for Evolution
Comparative embryology
Embryo: early, pre-birth stage of an organism’s development
Vertebrate embryos exhibit homologous structures during certain phases of development but become totally different structures in the adult forms

13. Evidence for Evolution
Comparative biochemistry-comparing molecules and amino acid sequences of different organisms
Geographic distribution
Biogeography-study of distribution of plants and animals around the world

14. Evidence for Evolution
Adaptation-trait shaped by natural selection that increases an organism’s reproductive success
Fitness-measure of contribution a trait makes to next generation
Ability to survive and reproduce
Camouflage, mimicry

15. Shaping Evolutionary Theory
Population genetics
Hardy-Weinberg principle=when allelic frequencies remain constant, a population is in genetic equilibrium
Conditions
Large population
No immigration or emigration
Random mating
No mutations
No natural selection

16. Shaping Evolutionary Theory
Genetic drift-any change in allelic frequencies in a population due to chance
Founder effect-small sample of population settles in location separated from the rest of the population
Bottleneck-population declines to very low number then rebounds

17. Shaping Evolutionary Theory
Modes of selection
stabilizing- favors intermediate phenotypes
Directional selection-favors an extreme
Disruptive selection-favors both extremes over intermediate

18. Shaping Evolutionary Theory
Sexual selection
Males and females differ in appearance
Preference by one sex of individuals of the other

19. Shaping Evolutionary Theory
Reproductive Isolation
Prezygotic isolating mechanisms
Geographical, ecological, behavioral
Postzygotic isolating mechanisms
Fertilization occurs but offspring cannot develop or reproduce

20. Shaping Evolutionary Theory
Speciation-the formation of a new and distinct species
Allopatric speciation-physical barrier divides one population into two or more populations
Sympatric speciation-species evolves into another without a physical barrier

21. Shaping Evolutionary Theory
Patterns of Evolution
Adaptive radiation-one species gives rise to many species in response to new habitat or other factors
Coevolution-evolving in close relationship with other species
Plant and insect relationship
Plant evolves chemical defense against insects, insects evolve resistance

22. Shaping Evolutionary Theory
Convergent evolution-unrelated species evolving similar traits

23. Shaping Evolutionary Theory
Theories of rate of speciation
Punctuated equilibrium-rapid spurts of genetic change
Gradualism-evolution proceeds in small steps