Evolution

1. Evolution Charles Darwin and Natural Selection

2. Vocab • Evolution - change in a kind of organism over time; process by which modern organisms have descended from ancient organisms • Theory - well-tested explanation that unifies a broad range of observations

3. Voyage of the Beagle (1839 - 1844) • Darwin’s Voyage - During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

4. Galapagos Islands • During his travels Darwin was amazed how different organisms were so well adapted to many different environments. • He saw patterns of diversity • Not just in living organisms, but also in fossil records. • The Galapagos Islands were a microcosm of Evolution

5. Darwin’s Finches

6. Idea’s that shaped Darwin’s Thinking • James Hutton and Charles Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present. • Thomas Malthus (English Economist) - reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. • Jean-Baptiste Lamarck 1809 - 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

7. Lamarck (His theory is wrong) • Tendency Toward Perfection • Innate tendency toward complexity and perfection • Birds acquired the urge to fly • Kept trying to fly • Use and Disuse • Using a trait (wings) causes them to become stronger and larger • Disuse causes it to disappear • Inheritance of Acquired Traits • Passing acquired traits from one generation to the next

8. Lamarck

9. Two things to know before talking about Natural Selection • In our world there is: • Natural Variation - differences among individuals of a species • And in order to understand Natural Selection you need to understand • Artificial selection - selection by humans for breeding of useful traits from the natural variation among different organisms

10. Vocab • struggle for existence - competition among members of a species for food, living space, and the other necessities of life • Fitness - ability of an organism to survive and reproduce in its environment • Adaptation - inherited characteristic that increases an organism’s chance of survival (increases an organism’s fitness) • survival of the fittest - process by which individuals that are better suited to their environment survive and reproduce most successfully; also called natural selection

11. Natural Selection • is the process by which individuals that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest • In order for natural selection to occur there must be: • Natural Variation • Struggle for existence • An adaptation that increases the fitness of one organism over another

12. Descent With Modification • Darwin’s proposed that over long periods natural selection produces organisms that: • Have different structures • Establish different niches • Or occupy different habitats • As a result species have descended, with changes from other species over time. • Darwin’s principle of Descent with modification

13. Questions • Key Concept What two ideas from geology were important to Darwin’s thinking? • Key Concept According to Lamarck, how did organisms acquire traits? • Key Concept According to Malthus, what factors limited population growth? • Why has Lamarck’s theory of evolution been rejected?

14. Evidence of Evolution

15. The Fossil Record

16. Geographical Distrib. of Species Common Descent

17. Homologous Body Structures • vestigial organorgan that serves no useful function in an organism

18. Vestigial Organ • organ that serves no useful function in an organism

19. Similarities in early development

20. Summary of Darwin’s Theory • There is variation (genetic…)between organisms which can be 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 organism is unique, each has different advantages and disadvantages in the struggle for existence. • 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 descent.

21. Chapter 16 GENES and VARIATION

22. Darwin’s Ideas Revisited • Darwin’s ideas had to be integrated with our new found information on Genetics.

23. Genes and Variation • Gene Pools - combined genetic information of all the members of a particular population • Relative Frequency - number of times an allele occurs in a gene pool compared with the number of times other alleles occur

24. Genes and Variation • There are two main sources of genetic variation: • Mutations – • What are the two main types of mutations? • Gene shuffling – • When and how does gene shuffling occur? • Big question: Do mutations and gene shuffling cause evolution? In other words do mutations and gene shuffling change the relative frequencies of alleles in a gene pool?

25. Genes and Variation • single-gene trait - trait controlled by a single gene

26. Genes and Variation • polygenic trait - trait controlled by two or more genes

27. Genetic Change (Evolution) Big Question Since mutations and gene shuffling does not change the relative frequencies of alleles in a population, what causes the change of allele frequencies in a population?

28. Single-gene Trait (Natural Sel.) Natural selection on single-gene traits can lead to changes in allele frequencies and, thus, to evolution.

29. Homework • Handout 16-1 and 16-2 • Thursday

30. What two processes can lead to inherited variation in populations? How does the range of phenotypes differ between single-gene traits and polygenic traits?

31. Polygenic Traits (Natural Sel.) • Natural selection can affect the distributions of phenotypes in any of three ways: • directional selection – form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve • stabilizing selection - form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end • disruptive selection - form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

32. Directional Selection

33. Stabilizing Selection Stabilizing selection takes place when individuals near the center of a curve have higher fitness than individuals at either end. This example shows that human babies born at an average weight are more likely to survive than babies born either much smaller or much larger than average.

34. Disruptive Selection • What will Disruptive Selection result in?

35. Genetic Drift • Genetic Drift - random change in allele frequencies that occurs in small populations • In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population. • founder effect - change in allele frequencies as a result of the migration of a small subgroup of a population

36. Genetic Drift and Founder Effect

37. Does Evolution occur all of the time? NO

38. Hardy-Weinberg principle • The principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change If there are no factors causing allele frequencies to change then the population is in…….. • genetic equilibrium - situation in which allele frequencies remain constant

39. Genetic Equilibrium • Five conditions are required to maintain genetic equilibrium from generation to generation: • random mating • the population must be very large • there can be no movement into or out of the population • no mutations (that filter into the gene pool) • no natural selection

40. Homework • Studyguide 16-3 • Test Chapter 15 and 16 on Tuesday

41. Describe how natural selection can affect traits controlled by single genes. • Describe three patterns of natural selection on polygenic traits. Which one leads to two distinct phenotypes? • How does genetic drift lead to a change in a population’s gene pool? • What is the Hardy-Weinberg principle?

42. When evolution DOES OCCUR • The process ofSPECIATION - formation of new species • Speciation has occurred when – population have become reproductively isolatedfrom one another • reproductive isolation - separation of species or populations so that they cannot interbreed and produce fertile offspring • Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.

43. Behavioral Isolation • form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding • Examples • Mating calls • Mating dances

44. Geographic Isolation • form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

45. Temporal Isolation • form of reproductive isolation in which two populations reproduce at different times

46. Speciation of Darwin’s Finches • Speciation in the Galápagos finches occurred by the: • founding of a new population • geographic isolation • changes in the new population’s gene pool • reproductive isolation • ecological competition