1. Principles of Evolution
Chapter 10-11
Principles of Evolution

2. Early evolutionary scientists
Carolus Linnaeus (Sweden) 1700s – developed a classification system; proposed new organisms come about through hybridization
Georges-Louis Leclerc de Buffon (France) 1700s – proposed that species shared ancestors and did not arise independently; suggested Earth was much older than 6000 years

3. Early evolutionary scientists
Erasmus Darwin (England) 1700s- proposed that all living things descended from a common ancestor; more complex forms come from less complex forms
Jean-Baptiste Lamarck (France) 1800s- organisms evolved toward perfection and complexity; species don’t go extinct, they evolve into other forms; believed in acquired characteristics

4. Theories of geologic change
Georges Cuvier (France)- theory of catastrophism: natural disasters shaped landforms and helped species become extinct; new species would move into the area
James Hutton (Scotland) – theory of gradualism: changes in landforms occur over long periods of time

5. Theories of geologic change
Charles Lyell (England) – published “Principles of Geology”; theory of uniformitarianism: processes that shape Earth are uniform through time; Earth changes gradually but at a constant rate

6. Darwin’s studies on the HMS Beagle
5 year collecting, mapping expedition to the South Pacific
Darwin’s collections helped him develop his evolutionary theory

7. Darwin’s studies in the Galapagos Islands
Most important observations
Studied and compared anatomy of species of reptiles, insects, birds, and flowering plants that were similar to those in other parts of the world
Studied fossils and found there were resemblances to modern organisms
Experienced earthquakes that pushed land up above sea level; geologic processes

8. Darwin’s studies in the Galapagos Islands

9. Darwin completes studies in England
Darwin found that all life struggles for existence
All life competes for food, space, shelter
Must escape predators
Only some live long enough to reproduce
Found different variations of traits in organisms of the same species

10. Darwin explanation for evolution
Artificial selection- technique in which breeders select particular traits that will be seen in offspring
Natural selection (Darwin’s theory)- mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce, and pass these traits on to the next generation
Each new generation is made up of organisms with the most favorable characteristics.

11. Natural Selection: 4 principles
Variation-heritable differences are the basis; result from genetic material
Overproduction-many offspring ensure that some will survive but causes competition among them
Adaptation-characteristic that gives an individual a better chance at survival; better chance at producing offspring
Descent with modification-over time, more individuals will have more of the “best” characteristics that allow them to survive and reproduce

12. Fitness Part of the natural selection process
Fitness- a measure of the ability to survive and produce more offspring relative to other members in the population

13. Adaptations can be compromises
Not all adaptations make the organisms perfectly suited to its environment
Ex: the Panda’s “thumb” is a wrist bone with a thumb-like function, used to hold bamboo

14. Evidence for evolution
A. Fossils
Provide a record of earlier life
Is incomplete but provide evidence of evolution
Can show step by step sequence of evolution for some species

15. Evidence continued B. Anatomical studies
Viewing basic limb (skeletal) structure can indicate a common ancestor
Different species often exhibit homologous structures ( modified body parts that are similar in structure, function, or both)
Analogous structures have similar functions but different structures and cannot be used to indicate evolutionary relationships

16. Evidence continued C. Functionless structures
Vestigial structures are reduced in function in modern organisms but may have been used by an ancestor
Continue to be inherited without function
Ex. Human appendix, ostrich wings, eyes in sightless species

17. Evidence Continued Embryological development
Similarities in embryological parts
Tail, gill slits present in all species
Become distinct only as development continues

18. Evidence continue E. genetic comparisons
More reliable than anatomical studies
Comparisons of DNA and RNA

19. Population genetics Populations evolve; individuals don’t
Can use genotypes of individuals in a population to calculate allelic frequency (% of an allele in the gene pool)
Populations are in genetic equilibrium when allelic frequencies remain unchanged

20. Populations genetics cont.
B. Changing genetic equilibrium leads to evolution
Anything that can disrupt or change an allelic frequency can lead to evolution
Mutations
Genetic drift: alteration of allelic frequency by chance (small populations)
Movement of individuals in and out of population (genes are gained or lost)

21. Population genetics cont.
C. Natural selection
Individuals more likely to survive and pass their genes on to the next generation
Allelic frequencies change from one generation to the next
Three types of natural selection
1.stabilizing-favors average individuals
2.directional-one extreme form of a trait is favored
3.disruptive-favors two extreme forms of a trait

22. Types of selection

23. Evolution vs. genetic equilibrium
1908 – Hardy-Weinberg Principle states that allele frequencies in a population will remain constant unless some factor causes the frequencies to change.
5 conditions to maintain genetic equilibrium
Random mating
Very large population
No immigration or emigration
No mutations
No natural selection

24. Evolution occurs If all 5 conditions of Hardy-Weinberg are NOT met
Any change in the gene pool will result in the evolution of the population

25. Evolution of species
speciation-evolution of a NEW species can occur only when either interbreeding or the production of fertile offspring is prevented

26. Isolating mechanisms that can result in speciation
Geographic isolation
Behavioral isolation
Temporal isolation

27. Geographic isolation Physical barriers can prevent interbreeding
Precipitation
Volcanic eruptions
Sea-level changes
1.changes mating behavior
2.changes chromosome number (polyploidy)

28. Behavioral isolation
Differences in courtship rituals or other reproductive strategies that involve behavior
If behaviors are not recognized, females will not accept mates

29. Temporal isolation 2 or more species reproduce at different times
If timing of courtship or release of gametes (sea animals or plants) is not specific, mates are not accepted by females (animals), or fertilization does not occur (sea animals and plants)

30. Patterns of evolution
Species diversify when introduced to new environments (adaptive radiation)
Divergent evolution pattern in which species that were all similar to the ancestral species become more distinct
1.different environments
2.different climates
C. Convergent evolution- the pattern of evolution in which distantly related organisms evolve similar traits
1.occupy similar environments
2.similar selection pressures