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Why do we have DIVERSITY on Earth? EVOLUTION Chapter 15 • Evolution… it’s a theory − Theory: Well-supported and tested explanation of phenomena that have occurred • What exactly is evolution? − Change over time − Process of modern organisms descending from ancient organisms Change Over Time Bill Nye: Evolution Change Over Time 1 Charles Darwin • Charles Darwin: Born February 12, 1809 Darwin’s Voyage on the H.M.S. Beagle • 1831 Darwin set sail from England on the H.M.S. Beagle as the ship’s naturalist • Collected evidence and made observations that led him to propose the hypothesis of EVOLUTION – how life changes over time Darwin’s Observations • Patterns of Diversity – Observed differences among organisms – Organisms were well suited for the environment they lived in 2 Darwin’s Observations Darwin’s Observations • The Galápagos Islands • Living Organisms & Fossils – Some fossils looked like organisms that were still alive – Other fossils he had ever seen before – Islands were close together but had very different climates – Some were hot and dry with low plants, another was wet with lots of tall plants – Darwin was fascinated with tortoises & iguanas • Tortoises varied from island to island • Their shells and necks were used to identify which island they inhabited Giant Tortoises of the Galápagos Islands Jeff Corwin Experience Pinta Pinta Island Marchena Intermediate shell Tower James Isabel a Organisms of the Galapagos Santa Cruz Santa Fe Floreana Hood Island Hood Saddle-backed shell Isabela Island Dome-shaped shell 3 Darwin Presents His Case for Evolution The Process of Evolution • Natural Selection drives evolution • Natural variation: all things are different – Found in all types of organisms in nature – Darwin proposed that much of this variation could be inherited The Process of Evolution • 3 Principles 1. Descent with modification. 2. The struggle for existence. 3. Survival of the fittest. − Those individuals best suited to their environment, survive, reproduce… passing on their traits to their offspring • Over time, natural selection results in changes in the inherited characteristics of a POPULATION. − These changes increase a species’ ability to survive in its environment. 1. Descent with Modification • Species today look differ from their ancestors • Each living species has descended, with changes, from other species over time − Common descent: There is a common ancestor to all living things 4 2. The Struggle for Existence • Species compete regularly for: food, living space, mates and other necessities • Some individuals are better than others in competition − EX: Cheetahs compete for prey; faster ones get more prey. − EX: Males deer fight for territory, winner lives there and mates with females – loser sent away 3. Survival of the Fittest • Fitness: the ability of an individual to survive and reproduce in its environment − Those better suited for their environment survive and reproduce; those poorly suited will die or have fewer offspring • The entire population becomes better suited for survival over time. What are Adaptations? • An adaptation is a genetically based trait that helps an organism survive in a particular environment − Adaptations may be anatomical structures or behaviors − Helps organisms become better suited to environment… better able to survive, reproduce, pass on traits Adaptations Examples WS How do adaptations benefit organisms? What are some examples of adaptions that you have seen? 5 Rock Pocket Mouse Evolution Packet Evolution in real-time! Review Natural Selection Simulation 1. What is a theory? 2. What is evolution? 3. What islands did Darwin observe to develop his theory of evolution? Will YOU survive?? 4. Describe natural selection. 5. What are adaptations? 6. Give an example of an adaptation. 6 Example: Survival of the Fittest PEPPERED MOTHS • Originally, most peppered moths had light coloration that camouflaged them against the light-colored trees and lichens where they lived • Industrial Revolution in England = lots of pollution. • Thus, trees blackened by soot Peppered Moth Activity Let’s see natural selection in real life! – Caused light-colored moths to die off due to predation. – The dark-colored flourished because of ability to hide on the darkened trees. 1. A genetic trait that increases and organism’s chance for survival in a specific environment 2. Gradual changes over long periods of time 1. Gradual changes over long periods of time 2. Process in which individuals that are best suited to their environment live and reproduce most successfully 3. What islands did Darwin observe to develop his theory of evolution? 3. A genetic trait that increases and organism’s chance for survival in a specific environment 4. Process in which individuals that are best suited to their environment live and reproduce most successfully 4. What islands did Darwin observe to develop his theory of evolution? 5. A well-supported and tested explanation of phenomena that have occurred 5. A well-supported and tested explanation of phenomena that have occurred 6. The ability of an individual to survive and reproduce in its environment 6. The ability of an individual to survive and reproduce in its environment 7. Give an example of an adaptation. 7. Give an example of an adaptation. 8. 8. Describe how the peppered moths are an example of natural selection. Describe how the peppered moths are an example of natural selection. 7 Darwin vs. Lamarck Let’s compare their theories on evolution. Lamarck’s Theory of Evolution Selective use of an organ led to change in that organ that was passed down to the next generation. 1. Gradual changes over long periods of time 2. Process in which individuals that are best suited to their environment live and reproduce most successfully 3. A genetic trait that increases and organism’s chance for survival in a specific environment 4. What islands did Darwin observe to develop his theory of evolution? 5. A well-supported and tested explanation of phenomena that have occurred 6. The ability of an individual to survive and reproduce in its environment 7. Give an example of an adaptation. 8. Describe how the peppered moths are an example of natural selection. Ideas that Shaped Darwin’s Thinking • Lamarck’s Acquired Characteristics: organisms could gain or lose traits during its lifetime by using or not using organs – Tendency toward perfection • EX: Ancestors of birds try to fly, increase wing size over many generations and then could fly Hypothesis was proven incorrect, but paved the way for other scientists by observing that organisms are adapted to their environment. – Use/disuse • EX: Birds don’t use wings, lose them – Traits are inherited • EX: Large wings passed to offspring 8 Can Selection be Artificial? Artificial Selection • Yes! • Nature provides variations within a species and • Humans have selected for the variations that they found useful. • Artificial Selection: We pick what we want to breed – We pick the BEST – Noticed this in farmers, picked largest hogs, fastest horses to breed – Breeding based on natural variation – This created wide ranges of plants and animals that looked very different from their ancestors Evidence for Evolution Who Wants to Live a Million Years • Fossil Record – Physical remains of ancient organisms that show how things have changed over time • Fossils show extinct transitional species connecting ancient species to modern species Natural Selection leads to change in populations… EVOLUTION! 9 Evidence for Evolution Evidence for Evolution • Geographic Similarities – Exposed to same conditions – Similar animals in different places came from different ancestors • Homologous Body Structures – Structures that develop from the same embryonic tissue but have different mature forms – Organisms have similar structure and function – EX: Wing, flipper, and arm—show how things have a common ancestor Turtle Alligator Bird Mammals Typical primitive fish Evidence for Evolution • Vestigial organs – Organs that once had a function, but no more – EX: Tail bone, Appendix, Wisdom teeth, ear muscles in humans Evidence for Evolution • Similarities in Embryology – Embryos look similar during early development – Certain types of cells and tissues develop in a similar order 10 Why is Evolution Possible? • Evolution is made possible because of genetic variation within a species. • Sources of genetic variation are: − Mutations: any change in a sequence of DNA − Gene Shuffling: crossing over and independent assortment during meiosis increase variation • Natural Selection acts on Phenotypes. Why is Evolution Possible? • Evolution acts on populations, not on individuals. − It’s how beneficial genes become more frequent over many generations. • Individual has many offspring because its phenotype is beneficial -- frequency of genes in a gene pool increases. • If an individual does not reproduce -- genes removed from gene pool. How are New Species Created? • Speciation occurs when there is Reproductive Isolation. − When members of two populations do not interbreed and produce fertile offspring • 3 Types of Reproductive Isolation 1. Behavioral Isolation 2. Geographic Isolation 3. Temporal Isolation Reproductive Isolation • Behavioral Isolation: two populations can interbreed but have different courtship rituals or other behavior − EX: Two birds whose habitats overlap don’t mate; mating songs are different. 11 Reproductive Isolation • Geographic Isolation: two species are separated by geographic barriers such as rivers, mountains, or bodies of water. Giant Tortoises of the Galápagos Islands Pinta Pinta Island Marchena Intermediate shell − EX: Islands separating Galapagos Tortoises and Finches Tower James Isabel a Santa Cruz Santa Fe Floreana Hood Island Hood Saddle-backed shell Isabela Island Dome-shaped shell Reproductive Isolation • Temporal Isolation: two or more species reproduce at different times − EX: Orchids in the rainforest-each species releases pollen at different times so they cannot pollinate one another Galapagos Finches • The finches of the Galapagos provide a key example for speciation. 1. Founding species of finch arrives on different islands. 2. The species of each island are geographically separated causing reproductive isolation. 3. Each population adapts differently and speciation occurs through natural selection. 12