1. Chapter 15-16 Darwin and the Theory of Evolution

2. 15-1 Charles Darwin Born 2/12/1809 Sailed on the Beagle in 1831 Sailed on the Beagle in 1831 Travels- particularly to the Galapagos Islands Travels- particularly to the Galapagos Islands Sailed around the world

3. Darwin’s Observations On Galapagos Islands – On Galapagos Islands – –Finches had different- shaped beaks from finches on the mainland –Tortoises had different- shaped shells from mainland tortoises The plants and animals were well-suited to their environment The plants and animals were well-suited to their environment Certain species live in one environment, and not another Certain species live in one environment, and not another

4. 15.2 Ideas that shaped Darwin’s thinking James Hutton and Charles Lyell James Hutton and Charles Lyell –Recognized that the Earth is millions of years old and still changing Thomas Malthus Thomas Malthus –If the human population continues to grow unchecked, then eventually there would not be enough resources

5. There was already a rich fossil record that was challenging the traditional thinking that all organisms exist as created. There was already a rich fossil record that was challenging the traditional thinking that all organisms exist as created. Charles Lyell’s Principles of Geology showed evidence of Earth’s extreme age. This book led Darwin to wonder if life could have changed very slowly over a long period of time.

6. Jean-Baptiste Lamarck One of the first scientists to notice living things have changed over time One of the first scientists to notice living things have changed over time Proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetimes Proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetimes These traits could then be passed on to their offspring These traits could then be passed on to their offspring Do you agree with this theory? Do you agree with this theory?

7. Checkpoint! Where is Darwin most known for his research? Where is Darwin most known for his research? –A. Caribbean IslandsC. Galapagos Islands –B. Hawaiian Islands D. English Islands What did Darwin consider as a reason for the different beaks on the island and mainland finches? What did Darwin consider as a reason for the different beaks on the island and mainland finches? –A. they had a common ancestor –B. they were the same species with mutations –C. they were not the same species –D. they had no common relatives

8. 15-3 Darwin Presents His Case observations on species led to his concept of evolution observations on species led to his concept of evolution In 1858 another scientist named Alfred Wallace sent an essay summarizing his thought on evolutionary change. This spurred Darwin to go ahead and publish his ideas. In 1858 another scientist named Alfred Wallace sent an essay summarizing his thought on evolutionary change. This spurred Darwin to go ahead and publish his ideas.

9. In 1859, Darwin published On the Origin of Species In 1859, Darwin published On the Origin of Species –In it, he proposed a mechanism for evolution he called natural selection – (process of change in species over time)

10. Natural Selection “Survival of the Fittest” “Survival of the Fittest” Members of the same population compete for food, living space, and other necessities of life Members of the same population compete for food, living space, and other necessities of life The predators that are successful in getting food and the prey that are successfully camouflaged or better protected will survive and pass on their DNA The predators that are successful in getting food and the prey that are successfully camouflaged or better protected will survive and pass on their DNA Fitness – the ability of an individual to survive and reproduce in its specific environment Fitness – the ability of an individual to survive and reproduce in its specific environment

11. Checkpoint! Whose idea stated that organisms changed through generations by passing on acquired characteristics? Whose idea stated that organisms changed through generations by passing on acquired characteristics? –A. MalthusB. Lyell –C. LamarckD. Hutton What was the reason Darwin decided to publish? What was the reason Darwin decided to publish? –A. he died –B. Wallace’s essay –C. Malthus theory was right –D. Hutton encouraged him

12. Adaptation Over time, natural selection results in changes in the inherited characteristics of a population Over time, natural selection results in changes in the inherited characteristics of a population These changes increase a species’ fitness in its environment These changes increase a species’ fitness in its environment Adaptation – inherited characteristic that can be physical or behavioral Adaptation – inherited characteristic that can be physical or behavioral

13. Artificial Selection Artificial Selection –Nature provides the variation, and humans selected those variations that they found useful This process has been used in choosing the best domesticated animals and plants to increase food production This process has been used in choosing the best domesticated animals and plants to increase food production

14. Checkpoint! What is the term for the ability to survive and reproduce? What is the term for the ability to survive and reproduce? –A. exerciseB. fitness –C. cardioD. fertility If a white moth and a black moth live in a forest of black-barked trees, and the white moths get hunted more regularly by birds, what is that called? If a white moth and a black moth live in a forest of black-barked trees, and the white moths get hunted more regularly by birds, what is that called? –A. competitionB. artificial selection –C. adaptationD. survival of the fittest

15. Evidence of Evolution Fossils Fossils –People in Darwin’s time understood that fossils were preserved remains of ancient organisms. Geographic Distribution of Living Things called biogeography Geographic Distribution of Living Things called biogeography –Species varied by location Homologous Body Structures Homologous Body Structures –Structures that have different mature forms but develop from the same embryonic tissues –Vestigial Organs – traces of homologous organs that serve no obvious purpose –Examples: limbs of reptiles, birds, and mammals Similarities in Embryology Similarities in Embryology –Early stages of embryos, many animals with backbones are similar

16. WARM UP How might vestigial organs provide clues to an animal’s evolutionary history? How might vestigial organs provide clues to an animal’s evolutionary history?

17. Chapter 16 – Evolution of Populations 16-1 Genes and Variations 16-1 Genes and Variations Genetic variation is studied in populations (group of same species that interbreed) Genetic variation is studied in populations (group of same species that interbreed) Gene pool – all genes that are present in a population Gene pool – all genes that are present in a population Relative frequency – number of times an allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur Relative frequency – number of times an allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur Evolution is change in the relative frequency of alleles in a population Evolution is change in the relative frequency of alleles in a population

18. Genetic Variation Two main sources of genetic variation Two main sources of genetic variation –Mutations Change in a sequence of DNA Change in a sequence of DNA –Gene shuffling Independent movement of chromosomes during meiosis and Crossing-Over Independent movement of chromosomes during meiosis and Crossing-Over

19. Checkpoint! Write down 2 different things that Darwin thought of as evidence for evolution. Write down 2 different things that Darwin thought of as evidence for evolution. What is the term for all the genes present in a population? What is the term for all the genes present in a population? –A. gene poolB. relative frequency –C. possible inheritanceD. gene shuffling Write down two sources of genetic variations? Write down two sources of genetic variations?

20. Single-Gene and Polygenic Traits The number of phenotypes produced for a trait depends on how many genes control the trait The number of phenotypes produced for a trait depends on how many genes control the trait –Single-gene trait Single gene with two alleles Single gene with two alleles Fewer phenotypes than polygenic traits Fewer phenotypes than polygenic traits Ex: widow’s peak Ex: widow’s peak –Polygenic trait Controlled by two or more genes (each with more than 2 alleles) Controlled by two or more genes (each with more than 2 alleles) Many different genotypes and phenotypes Many different genotypes and phenotypes Ex: height Ex: height

21. Distribution of Phenotypes Polygenic Traits Directional Selection Directional Selection –Individuals at one end of the curve have higher fitness than those in the middle or the other end Directional Selection Food becomes scarce. Low mortality, high fitness High mortality, low fitness

22. Stabilizing Selection Stabilizing Selection –Individuals near the center have higher fitness than those at either end of the curve. Key Percentage of Population Birth Weight Selection against both extremes keep curve narrow and in same place. Low mortality, high fitness High mortality, low fitness Stabilizing Selection

23. Stabilizing selection favors the norm, the common, average traits in a population. Look at the Siberian Husky, a dog bred for working in the snow. The Siberian Husky is a medium dog, males weighing 16-27kg (35- 60lbs). These dogs have strong pectoral and leg muscles, allowing it to move through dense snow. The Siberian Husky is well designed for working in the snow. If the Siberian Husky had heavier muscles, it would sink deeper into the snow, so they would move slower or would sink and get stuck in the snow. Yet if the Siberian Husky had lighter muscles, it would not be strong enough to pull sleds and equipment, so the dog would have little value as a working dog. So stabilizing selection has chosen a norm for the the size of the Siberian Husky. Stabilizing selection favors the norm, the common, average traits in a population. Look at the Siberian Husky, a dog bred for working in the snow. The Siberian Husky is a medium dog, males weighing 16-27kg (35- 60lbs). These dogs have strong pectoral and leg muscles, allowing it to move through dense snow. The Siberian Husky is well designed for working in the snow. If the Siberian Husky had heavier muscles, it would sink deeper into the snow, so they would move slower or would sink and get stuck in the snow. Yet if the Siberian Husky had lighter muscles, it would not be strong enough to pull sleds and equipment, so the dog would have little value as a working dog. So stabilizing selection has chosen a norm for the the size of the Siberian Husky.

24. Disruptive Selection Disruptive Selection –Individuals at the upper and lower ends of the curve have higher fitness than those in the middle. Disruptive Selection Largest and smallest seeds become more common. Number of Birds in Population Beak Size Population splits into two subgroups specializing in different seeds. Beak Size Number of Birds in Population Low mortality, high fitness High mortality, low fitness

25. Suppose there is a population of rabbits. The color of the rabbits is governed by two incompletely dominant traits: black fur represented by “B” and white fur represented by “b”. A rabbit with the genotype of “BB” would have a phenotype of black fur, a genotype of “Bb” would have gray fur (a display of both black and white) and a genotype of “bb” would have a phenotype of white fur. Suppose there is a population of rabbits. The color of the rabbits is governed by two incompletely dominant traits: black fur represented by “B” and white fur represented by “b”. A rabbit with the genotype of “BB” would have a phenotype of black fur, a genotype of “Bb” would have gray fur (a display of both black and white) and a genotype of “bb” would have a phenotype of white fur.genotypephenotypegenotypephenotype If this population of rabbits were put into an area that had very dark black rocks as well as very white colored stone, the rabbits with black fur would be able to hide from predators amongst the black rocks and the white furred rabbits would be able to hide in the white rocks, but the gray furred rabbits would stand out in both of the habitats and would suffer greater predation. If this population of rabbits were put into an area that had very dark black rocks as well as very white colored stone, the rabbits with black fur would be able to hide from predators amongst the black rocks and the white furred rabbits would be able to hide in the white rocks, but the gray furred rabbits would stand out in both of the habitats and would suffer greater predation. As a consequence of the selective pressures of their environment, our hypothetical rabbit population would be disruptively selected for extreme values of the fur color trait: white or black, but not gray. As a consequence of the selective pressures of their environment, our hypothetical rabbit population would be disruptively selected for extreme values of the fur color trait: white or black, but not gray.

26. Genetic Equilibrium Hardy-Weinberg principle If a population did not evolve, or change, the population would reach equilibrium – when allele frequencies stay the same If a population did not evolve, or change, the population would reach equilibrium – when allele frequencies stay the same Conditions required to reach equilibrium: Conditions required to reach equilibrium: –Random mating –Large population –No movement in or out of population –No mutations –No natural selection

27. Speciation Isolation prevents interbreeding between populations Isolation prevents interbreeding between populations –Behavioral isolation Different courtship rituals or reproductive strategies Different courtship rituals or reproductive strategies Example: remember the Drosophila fly songs? Example: remember the Drosophila fly songs? –Geographic isolation Two populations are separated by geographic barriers (rivers, mountains, oceans, etc..) Two populations are separated by geographic barriers (rivers, mountains, oceans, etc..) –Temporal isolation Species reproduce at different times (winter –vs- spring) Species reproduce at different times (winter –vs- spring)

28. Genetic Drift Genetic Drift –Random changes in allele frequencies that occur in a small population because of possible reproductive abilities of some and not others –Could result from a bottleneck or founder effect –Example: Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000 — but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

30. Bottleneck: an intense pressure or calamity reduces the numbers in a population Founder Effect: –Changes in allele frequencies as a result of migration of a small subgroup –Example: the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington's disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events

31. Checkpoint! Which of these is not a characteristic of a population in equilibrium? Which of these is not a characteristic of a population in equilibrium? –A. no mutationsB. no movement –C. no natural selectionD. non random mating When a daffodil blooms in the spring and a sunflower blooms in the summer, what kind of isolation keeps them from interbreeding? When a daffodil blooms in the spring and a sunflower blooms in the summer, what kind of isolation keeps them from interbreeding? –A. behavioralB. temporal –C. geographicD. physical