Evolution

1. Evolution • Change over time Evolution of Dance

2. Evolution • Change is directed by natural selection. • Changes occur over many generations

3. Early Theories: • Mid 1700’s – French Zoologist, said that living things do change through time. • Mid 1700’s – Swiss naturalist Charles Bonnet thought life began from scratch after periodic catastrophes. • 1809 - French aristocrat, Jean Baptiste de Lamarck believed species evolves from other species through acquired traits.  Unfortunately, his theory was entirely incorrect as they are not genetically determined.  

4. Lamarck’s Idea • Inheritance of acquired characteristics • behavior in a lifetime is passed along. • Ex: Giraffes evolved their long necks by each generation stretching further to get leaves • Proven wrong in the 1870’s by Weismann. Acquired traits are not genetically determined.

5. Charles Darwin, British naturalist1809 - 1882 • Observed differences in species over geographic regions (Galapagos Islands)

6. Darwin’s First TheoryDescent with Modification • Observed fossils were similar, but different from living organisms • Descent with Modification – newer forms appearing in the fossil record are modified descendants of older species

7. Darwin’s Second TheoryNatural Selection • A mechanism for change in a population. • Causes evolution in nature over millions of years • The environment plays a major role.

8. View Video Clip on Natural Selection: 4 factors

9. Genetic Variations • Organisms in a population have differences • Diversity is key • Less likely for extinction to occur in a changing environment if there are differences among organisms.

10. Sources of Variation • Mutations – flawed copies of genes. • Recombination – independent assortment of genes and crossing over in meiosis. • Sexual reproduction -Random fusion of gametes between two individuals (game of chance) • Environment can also play a role.

11. Overproduction of Offspring • More organisms are produced than will survive in a population. • Allows for greater chance of survival.

12. Struggle for Survival/Competition • Individuals compete for food, mates and space to live. • Individuals with favorable variations are more successful, will survive, and reproduce (survival of the fittest)

13. Survival and Reproduction • Favorable variations (adaptations) are passed on to the next generation, while unfavorable ones disappear. • Individuals that survive are most fit or better suited for their environment (also known as adapted

14. Questions on Natural Selection • What drives natural selection? • The environment • Is natural selection an active process? In other words, do you have a choice in being successful or not? • No, you can’t pick your traits. You are born with them. • Natural selection is one way evolution or change occurs. What is another way? • Selective breeding (not natural)

15. Adaptation Video Fish Adaption Video Polar Bears

16. Natural Selection Leads to Adaptations and Fitness • Adaptation - An inherited variation (favorable trait) that increases a population’s chance of survival in a given environment. • Galapagos finches – each beak works best in their given environment. Infer what their environments look like. • Fitness - An organism that is naturally selected by the environment is said to be adapted, or better suited for survival.

18. Population • A group of many individuals of the SAME SPECIES living in the same area and sharing a common gene pool. • Trait may be favorable or unfavorable • They share some important features but differ in other features.

19. Gene Pool • The sum of all the genetic information (Genes) carried by members of a population.

20. Population Genetics • Individuals can NOT evolve, only populations can. • Evolution is the gradual change of the allele frequencies found in a population. • Allele frequency – percentage of an allele in a gene pool. In other words, how often genes (traits) are seen. • Favorable genes will be seen more frequently.

21. Hardy-Weinberg Genetic Equilibrium • Two scientists that showed allele frequencies in a population tend to remain the same over generations unless acted on by outside influences. • In other words, populations do no evolve, remain constant.

22. Equilibrium is based on theoretical population where • No mutations occur • No migration occurs • The population is large • Individuals mate randomly • Selection does not occur (natural or artificial)

23. Real Populations vs. Theoretical • Real populations such as a flock of mallards violate the 5 conditions necessary for genetic equilibrium. • This leads to variations among organisms, natural selection and evolution.

24. 1. Mutation-Random inheritable change in genetic material • Can cause new alleles, or forms of a trait • Change the sequence of a gene • Can be harmful or fatal, possibly neutral or may be a benefit in a changing environment.

25. 2. Migration – the movement of individuals in or out of a population • Causes gene flow - the mixing of genes as a result of migration between populations • Movement in enhances variation, while movement out decreases variation.

26. 3. Genetic Drift-random change in allele frequency due to chance • Small populations (<100) most affected (probability – smaller a sample, the greater the chance of deviation from the expected result) • Tendency for alleles to become lost or fixed • Natural disasters • New arrivals to an isolated area

27. 4. Nonrandom Mating – select mate • Mate selection can be influenced by geographic proximity resulting in mates with some degree of kinship. • Individuals also can select a mate based on similar characteristics. (nonrandom mating affects genotypes but not overall allele frequency)

28. 5. Natural Selection – most fit survive and pass down their trait

29. Types of Selection: • Normal graph:

30. Stabilizing selection • Favors average phenotypes over extremes For example, plant height might be acted on by stabilizing selection. A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be more susceptible to wind damage. Combined, these two selection pressures select to maintain plants of medium height. The number of plants of medium height will increase while the numbers of short and tall plants will decrease.

31. Directional selection • Favors phenotypes at one extreme Using the familiar example of giraffe necks, there was a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks.

32. Disruptive selection • Takes place when extremes of phenotypic range are selected • Eliminates the average • RARE For example, imagine a plant of extremely variable height that is pollinated by three different pollinators, one that was attracted to short plants, another that preferred plants of medium height and a third that visited only the tallest plants. If the pollinator that preferred plants of medium height disappeared from an area, medium height plants would be selected against and the population would tend toward both short and tall, but not medium height plants. Such a population, in which multiple distinct forms or morphs exist is said to be polymorphic.

34. Examples of Evolution in Action • Bacterial resistance to antibiotics

35. Examples of Evolution in Action • Mosquito resistance to insecticides

36. Examples of Evolution in Action • Peppermoth changes with the industrial revolution.