Learning Targets Describe the factors that Darwin considered when developing his Theory of Evolution. Explain the process of natural selection and how it leads to descent with modification. Describe the significance of genetic variation within a population and identify sources of genetic variation. Describe how evolution occurs through changes in gene pools, including genetic drift, gene flow, and sexual selection.
Darwin and Natural Selection
Evolution is a Theory – Just like Einstein's Theory of General Relativity, which helps to explain gravity! Evolution is a well supported explanation of phenomena that have occurred in the natural world A theory in science is a well tested hypothesis, not just a guess
Charles Darwin (1809-1882) Sailed around the world 1831-1836
What did Darwin’s travels reveal What did Darwin’s travels reveal The diversity of living species was far greater than anyone had previously known!! These observations led him to develop the theory of evolution!!
Diversity on the Galapagos Diversity on the Galapagos Each island had its own type of tortoises and birds that were clearly different from other islands.
Galapagos Tortoise
Influences on Darwin’s Theories Influences on Darwin’s Theories Theories of geologic change set the stage for Darwin’s theory Fossils: traces of organisms that existed in the past. Theory of catastrophism states that natural disasters like floods and volcanic eruptions have shaped landforms and caused species to go extinct. Theory of gradualism states that changes in landforms resulted from slow changes over a long period of time. Theory of uniformitarianism states that the geologic processes that shape Earth are uniform through time (Charles Lyell’s theory).
Influences on Darwin’s Theories Lyell argued that the earth is many millions of years layers of rock take time to form processes such as volcanoes and earthquakes shaped the earth and still occur today
Influences on Darwin’s Theories Influences on Darwin’s Theories Jean-Baptiste Lamarck: Theory of acquired characteristics Organisms acquired traits by using their bodies in new ways These new characteristics were passed to offspring Lamark was wrong!
Influences on Darwin’s Theories Influences on Darwin’s Theories Thomas Malthus If the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone
Influences on Darwin’s Theories Artifical Selection: Process in which humans change a species by breeding it for certain traits. Examples: Dog breeds, livestock, crops, vegetables, ect.
Darwin’s The Origin of Species (1859) Darwin’s The Origin of Species (1859) Other naturalists, like Alfred Wallace, were developing the same theory as Darwin’s Even though Darwin was afraid of the Church’s reaction to his book he wanted to get credit for his work.
Summary of Darwin’s Theory of Evolution by Natural Selection Summary of Darwin’s Theory of Evolution by Natural Selection 1. Organisms differ; variation is inherited 2. Organisms produce more offspring than survive 3. Organisms compete for resources 4. Organisms with advantages survive to pass those advantages to their children (“survival of the fittest”) 5. Species alive today are descended with modifications from common ancestors
Summary of Darwin’s Theory POINT 1 of 5 Organisms differ; variation is inherited OBSERVED OBSERVED THEORY ? HYPOTHESIS Discuss …
Summary of Darwin’s Theory POINT 2 of 5 Organisms produce more offspring than survive OBSERVED OBSERVED THEORY ? HYPOTHESIS Discuss …
Summary of Darwin’s Theory POINT 3 of 5 Organisms compete for resources OBSERVED OBSERVED THEORY ? HYPOTHESIS Discuss …
Summary of Darwin’s Theory POINT 4 of 5 Organisms with advantages survive to pass those advantages to their children OBSERVED OBSERVED THEORY ? HYPOTHESIS Discuss …
Summary of Darwin’s Theory POINT 5 of 5 Species alive today are descended with modifications from common ancestors. THEORY, much evidence exists OBSERVED THEORY ? HYPOTHESIS
End of Day 1 Notes Write a two sentence summary of the first half of your notes in the summary section.
Bellringer Who is Charles Darwin? What influenced Darwin’s Theory of Evolution? What does descent with modification mean?
What is evolution? changes in living organisms over time explains how modern organisms have descended from ancient organisms
Fitness and Adaptation Fitness and Adaptation Organisms compete for limited resources and some organisms are more “fit” than others Fitness – the ability of an individual to survive and reproduce in its specific environment Adaptation – any inherited characteristic that increases an organism’s chance of survival, including reproduction
What determines survival? What determines survival? Traits that help individuals survive survive predators survive disease compete for food compete for territory Traits that help individuals reproduce attracting a mate compete for nesting sites successfully raise young
Natural Selection There is variation (difference in the physical traits of an individual from those of other individuals in the group) in traits. For example, some beetles are green and some are brown. There is differential reproduction. Since the environment can’t support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.
Natural Selection There is heritability. The surviving brown beetles have brown baby beetles because this trait has a genetic basis (trait is passed down from one generation to the next). End result: Natural Selection The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. If this process continues, eventually, all individuals in the population will be brown.
Natural Selection Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment. Species: Group of organisms so similar to one another that they can reproduce and have fertile offspring.
Sources of Genetic Variation Genetic Variation is stored in a populations Gene Pool, which is the combined alleles of all of the individuals in a population. Each allele exists at a certain rate in a population. Allele Frequency, is a measure of how common a certain allele is in the population.
Sources of Genetic Variation Sources of Genetic Variation Gene flow – movement of genes from one population to another (migration) Mutation – any change in a sequence of DNAMain Source Some mutations can affect an organism’s fitness while others have no effect on fitness. Recombination –(occurs during meiosis) Main Source Independent assortment Crossing over Sexual reproduction
Evolution as Genetic Change Natural selection determines which alleles are passed from one generation to the next. As a result, it can change the relative frequencies of alleles in a population over time. Evolution is any change in the relative frequencies of alleles in a population’s gene pool. Evolution acts on populations, not on individuals. *Remember: Populations include individuals of the same species living in an area.
Genetic Drift Natural selection is not the only source of evolutionary change Genetic drift – random change in allele frequency In small populations, individuals that carry a particular allele may leave more descendants 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.
Bottleneck Effect Mechanism of genetic drift, occurs after an event drastically reduces the size of a population. This causes the population to have very little variation. The reason for this is that certain alleles have become fixed in the population and others have been lost.
Founder Effect Occurs when a small group of individuals colonizes a new habitat. Members of the colony may carry alleles in different relative frequencies than the larger population from which they came. If so, the population that they found will be genetically different from the parent population.
Sexual Selection Certain traits increase mating success, so these traits will be passed down from generation to generation.