Chapter 15: Darwin’s Theory of Evolution

1. Chapter 15: Darwin’s Theory of Evolution

2. Section 15-1: the Puzzle of Life’s Diversity • Scientists have tried to understand how did the variety of organisms on Earth arise. • The variety of living things is called biological diversity. • The collection of scientific facts observations, and hypothesis are known as the evolutionary theory. • Evolution: change over time, process by which modern organisms have descended from ancient organisms. • Theory: a well supported testable explanation of phenomena that have occurred in the natural world.

3. Darwin and Evolution • Charles Darwin was the biggest contributor to the theory of evolution. • He was well educated and interested in the natural history. • Darwin made most of his observations and collected evidence that lead him to propose a revolutionary theory during his travels on the H.M.S. Beagle.

4. Patterns of Diversity Organism’s are suited for their environments. Living organisms and fossils Fossils of organisms resembled organisms that were still alive. Darwin’s Observations

5. Darwin’s Observations • The Gálapagos Islands • Located 1000km west of South America, although close together, the islands have different environments. • Organisms, although the same species, could be identified by island because of their characteristics.

6. Darwin’s Observations • Darwin observed that the characteristics of many organisms varied noticeably among the different islands. • He wondered if the organisms in the islands were once members of the same family.

7. Section 15-2: Ideas That Shaped Darwin’s Thinking • Many ideas were being discussed during Darwin’s time that were changing the conventional way of thinking. Discoveries in Geology and other fields, these helped Darwin understand his observations. • Hutton’s Theory of Geological Change: • Most geological changes occur very slow, thus the Earth had to be much older than a few thousand years old. • Lyell’s Principles of Geology: • The processes that shaped the Earth millions of years ago, are still shaping the world now – scientists must use these events to explain current observations. • Lamarck’s Theory of Evolution: • Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species. • Population Growth: • Thomas Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. • This statement made Darwin question: What determines what organisms survive?

8. Section 15-3: Darwin Presents His Case • Darwin explained his observations by a process that would later be called evolution. • He did not publish his work immediately because his proposition challenged the scientific ideas of his time. • After communication with a fellow naturalist, Darwin had the incentive to publish his work.

9. Natural Variation and Artificial Selection • Darwin began his explanation by leaving behind the idea that organisms are perfect and unchanging. • He stated that there was a natural variation among species. • Natural variation is the differences among the individuals of a species.

10. Natural Variation and Artificial Selection • Darwin observed farmers and breeders and saw that they were using the “best” characteristics found through natural variation. • He called this process artificial selection, because it was the farmers and the breeders making the selection, not nature. • Artificial Selection utilizes the variation provided by nature, and humans select the variations they found useful.

11. Artificial Selection Pepito 

12. Evolution by Natural Selection • Darwin compared the Artificial Selection process, to what would be happening in nature. • He based his hypothesis on: • The Struggle for Existence • Survival of the Fittest • Decent with Modifications

13. The Struggle for Existence • Members of the same species compete for living necessities

14. Ability of an individual to survive and reproduce in its specific environment. This ability is a result of adaptation, which is an inherited characteristic that increases the chances of survival. Survival of the Fittest

15. All living species have descended, with changes, from other species over time. Decent with Modifications

16. Evidence of Evolution • Darwin stated that living things have been evolving on Earth for millions of years. Evidence for this process could be found from various sources: • Fossil Record • Geographical Distribution • Homologous Structures • Similarities in Early Development

17. Darwin proposed that Earth was hundred of million years old. During this time, he stated, countless species of many different forms had appeared on Earth, lived for a time, and then vanished. Fossils that had formed in the different layers of rock were evidence of this gradual change. Fossil Record

18. Although Darwin found different animals on different continents, when he looked at similar environments he saw similarities in structures and behaviors. Even though they came from different ancestors, there were similar environmental pressures of natural selection. Geographical Distribution

19. Homologous Structures • Researches had noticed similarities among body parts of animals with backbones. • Scientist hypothesize that structures have adapted for organisms to survive in different environments. • Despite having different functions, all limbs develop from the same clump of cells.

20. Similarities in Early Development

21. Summary of Darwin’s Theory • Individual organisms in nature differ from one another. Some of this variations are inherited. • Organisms in nature produce more offspring than can survive, and many of those that survive do not reproduce. • Because more organisms are produced than can survive, members of each species must compete for limited resources. • Because each organisms is unique, each has different advantages and disadvantages in the struggle for existence.

22. Summary of Darwin’s Theory • Individuals best suited to their environment survive and reproduce most successfully. The characteristics that make them best suited to their environment are passed on to offspring. Individuals whose characteristics are not as well suited to their environment die or leave fewer offspring. • Species change over time. Over long periods, natural selection causes changes in the characteristics of a species, such as in size and form. New species arise, and other species disappear. • Species alive today have descended with modifications from species that lived in the past. • All organisms on Earth are united into a single tree of life by common descendent.

23. Chapter 16: Evolution of Populations

24. Section 16-1: Genes and Variation • Darwin worked with the disadvantage of knowing Mendel’s findings. • He worked on his theory in the 1830’s, but Mendel’s work was not recognized until the 1900’s. • Today, geneticist, molecular biologists, and evolutionary theory work together to explain how inheritable variations appears and how natural selection operates on that variation.

25. Individuals that live in the same population interbreed and thus share common genes. A population is a collection of individuals of the same species. A combination of the available genetic information is called a gene pool. A gene pool usually contains two or more alleles and its an inheritable trait. Gene Pools

26. Gene Pools • The relative frequency of an allele is the number of times that alleles occurs in a gene pool compared with the number other alleles occur.

27. Sources of Variation • Two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction. • Mutations: any change in the DNA. Many mutations do not cause a change in the phenotype, but others might. Changes on the phenotype, can change the individual’s fitness. • Gene Shuffling: independent movement of chromosomes during meiosis and crossing over furthers the number of phenotypes.

28. Single-Gene and Polygenic Traits • The number of phenotypes produced from a given trait depends on how many genes control the trait. Widow’s Peak Single-Gene Trait Polygenic Trait

29. Section 16-2: Evolution as Genetic Change • Natural selection on single-gene traits can lead to changes to allele frequencies and thus to evolution. Initial Population Generation 10 Generation 20 Generation 30 80% 10% 10%

30. Section 16-2: Evolution as Genetic Change • Natural selection on single-gene traits can lead to changes to allele frequencies and thus to evolution. Initial Population Generation 10 Generation 20 Generation 30 80% 80% 10% 10% 20%

31. Section 16-2: Evolution as Genetic Change • Natural selection on single-gene traits can lead to changes to allele frequencies and thus to evolution. Initial Population Generation 10 Generation 20 Generation 30 80% 80% 70% 10% 10% 20% 30%

32. Section 16-2: Evolution as Genetic Change • Natural selection on single-gene traits can lead to changes to allele frequencies and thus to evolution. Initial Population Generation 10 Generation 20 Generation 30 80% 80% 70% 40% 10% 10% 20% 30% 60%

33. Natural Selection on Polygenic Traits • Natural Selection can affect the distributions of phenotypes in any of ways: directional selection, stabilizing selection, or disruptive selection.

34. Genetic Drift • In small populations, individuals that carry a particular allele may leave more descendents than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population.

35. Evolution Versus Genetic Equilibrium • Scientists wanted to know if there is any possibility where evolution would not happen. • Using the Hardy-Weinberg equation, alleles in a population will remain constant unless one or more factors cause those frequencies to change. • When allele frequencies remain constant, it is called genetic equilibrium.

36. Hardy-Weinberg principle • Five conditions are required to maintain genetic equilibrium from generation to generation: • Random Mating • Large Population • No Movement Into or Out of the Population • No Mutations • No Natural Selection

37. Section 16-3: The Process of Speciation • Factors such as natural selection and chance events can change the relative frequencies of alleles in a population. • When these events and others happen, the process of speciation can occur. • Speciation is the forming of a new species.

38. Isolation Mechanisms • As new species evolve, populations become reproductively isolated from each other. • When two members of two populations cannot interbreed and produce fertile, offspring.

39. Isolating Mechanisms Behavioral Isolation Temporal Isolation Geographical Isolation

40. Speciation in Darwin’s Finches • Speciation in the Galápagos finches occurred by various events: • Founders Arrive: • Finches from South America arrived on one of the islands. • Separation of Populations: • Islands are far away from each other and the finches cannot cross over. • Changes in the Gene Pool: • Finches adapted to the conditions in each particular island. • Reproductive Isolation: • After being separated, different island finches would not mate. • Ecological Competition: • During dry seasons, finches most different would be better suited to survive. • Continued Evolution: • Over time, these environmental pressured have developed 13 different species of finches.