1. Evolution

2. Outline
Early Evolutionary Concepts
Darwin
Microevolution
Mutations
Chromosomal Changes
Migration and Genetic Drift
Rate of Evolution
Macroevolution
Role of Hybridization

3. Early Evolutionary Concepts
By end of 18th century, many prominent biologists believed heredity changes in populations over long periods of time occurred as a result of the inheritance of acquired characteristics.
Long necks of giraffes.
Copyright © McGraw-Hill Companies Permission
Required for Reproduction or Display

4. Charles Darwin
Accepted position as assistant naturalist on HMS Beagle to voyage around the world and chart coastlines.
Read Charles Lyell’s book that theorized the earth was much older than previously believed.
Guided by ideas of Malthus.
Populations grow geometrically until food supplies and other resources limit growth.

5. Evidence for Evolution
Homologous Characteristics
Common Ancestry
Convergent Evolution
Protein Structure and Relationships
Fossil Record
Copyright © McGraw-Hill Companies Permission
Required for Reproduction or Display

6. Microevolution
Darwin observed that animal breeders, through artificial selection, changed populations of domestic animals by retaining those with desirable traits.
Reasoned that in nature, individuals best adapted to available resources would increase in number in succeeding generations.
Natural Selection

7. Microevolution
Darwin based natural selection on :
Overproduction of Offspring.
Struggle for Resources and Thus Survival.
Inheritance and Accumulation of Favorable Variations.
Differential Survival and Reproduction.

8. Mutations
General characteristics of a population will eventually change if the environment, or other factors, favor certain heredity variations, and disfavor others.
No permanent change occurs unless there is inheritable variation.
Arise via mutations.

9. Mutations
Mutations arise via:
Chromosome Deletions
Chromosome Translocations
Chromosome Inversions
Generally, the mutation rate for a specific gene remains relatively constant in the absence of environmental changes.
Most mutations are harmful.

10. Chromosomal Changes

11. Migration and Genetic Drift
Migration - Gene flow occurs between populations when individuals or gametes move from one population to another.
Genetic Drift
Changes in the genetic make-up of a population due to random events.
May occur as a given gene fluctuates due to meiosis and gamete production.

12. Rate of Evolution
Darwin believed evolution by natural selection was slow and gradual.
Many contemporary biologists believe theory of punctuated equilibrium.
Major changes occurred in spurts.

13. Macroevolution
Reproductive Isolation
If new genes are produced in a freely interbreeding population, they may gradually be spread throughout the population.
If some barrier divides the population, two new populations eventually may become distinct from each other.

14. Macroevolution
Geographic Isolation
Geographic, or other, isolation of two populations prevents gene flow between the two populations.
Random mutations, which are rarely identical, then spread only throughout the population in which they arise.

15. Macroevolution
Ecological Isolation
Ecological factors such as climate or soils may play a role in isolation, as do time and mechanical isolating factors.
As a result, related species can be sympatric without genes being exchanged.

16. Role of Hybridization in Evolution
Hybrids may be significant or important in evolutionary change, depending on how the characteristics of the parents were combined.
Introgression - Backcrossing between hybrid and parent.
Polyploidy - New cell wall fails to develop between two daughter cells.
Sterility - Chromosomes do not pair up correctly.

17. Sterile Hybrids may reproduce asexually.
Apomixis
Sterile Hybrids may reproduce asexually.
Apomixis includes the development and production of seeds without fertilization.
May be highly successful.
Dandelions and Wild Blackberries
Copyright © McGraw-Hill Companies Permission
Required for Reproduction or Display

18. Review
Early Evolutionary Concepts
Darwin
Microevolution
Mutations
Chromosomal Changes
Migration and Genetic Drift
Rate of Evolution
Macroevolution
Role of Hybridization

19. Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display