Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 15-16 Darwin and the Theory of Evolution 15-1 Charles Darwin Born 2/12/1809 • Sailed on the Beagle in 1831 • Travels- particularly to the Galapagos Islands Sailed around the world Darwin’s Observations • The plants and animals were well-suited to their environment • Certain species live in one environment, and not another • On Galapagos Islands – – Finches had differentshaped beaks from finches on the mainland – Tortoises had differentshaped shells from mainland tortoises 15.2 Ideas that shaped Darwin’s thinking • James Hutton and Charles Lyell – Recognized that the Earth is millions of years old and still changing • Thomas Malthus – If the human population continues to grow unchecked, then eventually there would not be enough resources • 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. Jean-Baptiste Lamarck • 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 These traits could then be passed on to their offspring Do you agree with this theory? Checkpoint! • Where is Darwin most known for his research? – A. Caribbean Islands – B. Hawaiian Islands C. Galapagos Islands D. English Islands • 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 15-3 Darwin Presents His Case • 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 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) Natural Selection • “Survival of the Fittest” • 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 Fitness – the ability of an individual to survive and reproduce in its specific environment Checkpoint! • Whose idea stated that organisms changed through generations by passing on acquired characteristics? – A. Malthus – C. Lamarck B. Lyell D. Hutton • What was the reason Darwin decided to publish? – A. he died – B. Wallace’s essay – C. Malthus theory was right – D. Hutton encouraged him Adaptation • Over time, natural selection results in changes in the inherited characteristics of a population • These changes increase a species’ fitness in its environment • Adaptation – inherited characteristic that can be physical or behavioral • 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 Checkpoint! • What is the term for the ability to survive and reproduce? – A. exercise – C. cardio B. fitness D. 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? – A. competition – C. adaptation B. artificial selection D. survival of the fittest Evidence of Evolution • Fossils – People in Darwin’s time understood that fossils were preserved remains of ancient organisms. • Geographic Distribution of Living Things called biogeography – Species varied by location • 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 – Early stages of embryos, many animals with backbones are similar WARM UP • How might vestigial organs provide clues to an animal’s evolutionary history? Chapter 16 – Evolution of Populations • 16-1 Genes and Variations • Genetic variation is studied in populations • • • (group of same species that interbreed) 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 Evolution is change in the relative frequency of alleles in a population Genetic Variation • Two main sources of genetic variation – Mutations • Change in a sequence of DNA – Gene shuffling • Independent movement of chromosomes during meiosis and Crossing-Over Checkpoint! • 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? – A. gene pool B. relative frequency – C. possible inheritance D. gene shuffling • Write down two sources of genetic variations? Single-Gene and Polygenic Traits • The number of phenotypes produced for a trait depends on how many genes control the trait – Single-gene trait • Single gene with two alleles • Fewer phenotypes than polygenic traits • Ex: widow’s peak – Polygenic trait • Controlled by two or more genes (each with more than 2 alleles) • Many different genotypes and phenotypes • Ex: height Distribution of Phenotypes Polygenic Traits • 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 • Stabilizing Selection – Individuals near the center have higher fitness than those at either end of the curve. Stabilizing Selection Key Low mortality, high fitness High mortality, low fitness Birth Weight Selection against both extremes keep curve narrow and in same place. • 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 (3560lbs). 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. • Disruptive Selection – Individuals at the upper and lower ends of the curve have higher fitness than those in the middle. Disruptive Selection High mortality, low fitness Population splits into two subgroups specializing in different seeds. Beak Size Number of Birds in Population Low mortality, high fitness Number of Birds in Population Largest and smallest seeds become more common. Beak Size • 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. • 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. Genetic Equilibrium Hardy-Weinberg principle • If a population did not evolve, or change, the population would reach equilibrium – when allele frequencies stay the same • Conditions required to reach equilibrium: – Random mating – Large population – No movement in or out of population – No mutations – No natural selection Speciation • Isolation prevents interbreeding between populations – Behavioral isolation • Different courtship rituals or reproductive strategies • Example: remember the Drosophila fly songs? – Geographic isolation • Two populations are separated by geographic barriers (rivers, mountains, oceans, etc..) – Temporal isolation • Species reproduce at different times (winter –vsspring) • 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. 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 Checkpoint! • Which of these is not a characteristic of a population in equilibrium? – A. no mutations B. no movement – C. no natural selection D. 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? – A. behavioral – C. geographic B. temporal D. physical