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Darwin’s Theory of Evolution Chapter 16 Voyage of the Beagle 1831 – set sail around the world Collected plant and animal specimens Explained how modern organisms evolved over long periods of time through descent from common ancestors 3 Distinct Patterns of Biodiversity Species vary Globally Species vary locally Species vary over time Species Vary Globally Different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe Rhea Ostrich Emu Patterns of Diversity Visited Argentina and Australia – Very similar ecosystems = both grasslands – Yet very different organisms at each – Why no rabbits in Australia and no kangaroos in Argentina? Species Vary Locally Different, yet related, animal species often occupied different habitats within a local area The Galapagos Islands Islands very close together but very different climates Darwin studied land tortoises and marine iguanas The shape of a tortoise’s shell could be used to identify which island it came from Giant Tortoises of the Galápagos Islands Section 15-1 Pinta Pinta Island Tower Marchena Intermediate shell Fernandina James Santa Cruz Isabela Santa Fe Hood Island Floreana Isabela Island Dome-shaped shell Hood Saddle-backed shell Darwin’s Finches Back in England Darwin observed the characteristics of many animals and plants varied noticeably among the different islands of the Galapagos Hypothesis – These separate species evolved from a South American ancestor after being isolated from one another Species Vary Over Time Some fossils of extinct animals were similar to living species Some fossils looked like nothing alive today Why had so many of these species disappeared? How were they related to living species? Contributing to Darwin James Hutton – Looked at geological forces and rock formations – Earth was shaped by geological processes that work very slowly…millions of years Earth had to be millions of years old Charles Lyell Principles of Geology Uniformitarianism – Laws of nature are constant over time Darwin witnessed these events – Volcanoes – Earthquakes Lyell explained how these events formed the Earth If Earth could change over time, could life change too? Lamarck’s Theory of Evolution Organisms acquired traits from use and disuse and then passed these traits on – Organisms had a tendency for perfection – Use and Disuse – Inheritance of Acquired Traits Lamarck’s Theory Thomas Malthus Realized that babies being born faster than people dying Hypothesized – If the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone Darwin applied this to other organisms Darwin’s Case Didn’t want to publish findings Alfred Russel Wallace, naturalist, published an essay on evolutionary change On the Origin of Species Natural Variation and Artificial Selection Every species exhibits some variation – Natural Variation Darwin noted that farmers used selective breeding Artificial selection – nature provides the variation and humans selected those variations for offspring Evolution by Natural Selection Struggle for Existence – Malthus – Organisms competing for resources Evolution by Natural Selection Variation and Adaptation – Individuals have natural variations – Some better suited to life in their environments than others – Adaptation – any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment Bactrian camel Camels have many adaptations that allow them to live successfully in desert conditions. Sea Otters Sea otters spend almost their entire lives in water. They eat, sleep, and even have their babies in water. How is their fur adapted to keep them warm? Why is it a critical situation when otters encounter oil spills? Platypus How are platypuses adapted for the time they spend in water? Katydids Butterflies and Mimicry One butterfly is a Monarch and one is a Viceroy. Can you tell the difference? Why might butterflies adapt to look the same? Insect Eating Pitcher Plant Palo verde tree bark What adaptation does this plant have? Hint: It has to do with the bark. Evolution by Natural Selection Survival of the Fittest – Each individual exhibits fitness which is a result of adaptation – Fitness = how well an organism can survive and reproduce in an environment Survival of the Fittest – difference in rates of survival and reproduction Natural Selection Natural selection – only certain individuals are “selected” to reproduce – Environment Chooses! Occurs when… – Struggle for existance – Variation and adaptation – Survival of the fittest Natural Selection results in changes in the inherited characteristics of a population, which increases a species’ fitness Natural Selection Descent with Modification Over time, organisms fit into different niches and have descended with changes… Descent with Modifications Implies that everything is related to each other… Common Descent Darwin concluded that you could make one large tree of life for all living things Evidence of Evolution Fossil Record Geographic Distribution of Living Species Homologous Body Structures Similarities in Early Development Physical remains of organisms Common ancestral species Similar Genes Similar Genes Fossils Many recently discovered fossils form series that trace the evolution of modern species from extinct ancestors Geographic Distribution of Living Things Biogeography – where organisms live now and where they and their ancestors lived in the past Closely related species differentiate in slightly different climates (ex. Galapagos) Distantly related species develop similarities in similar environments (ex. Flightless birds) – Same ecological pressures → similar pressures of natural selection → Evolved common traits Homologous Body Structures Turtle Alligator Bird Mammals Typical primitive fish Homologous structures have developed from the same embryonic tissues but have different mature forms – Descended, with modification, from common ancestors Homologous Body Structures Homologous Body Structures Homologous Body Structures – different function yet similar structure Analogous Body Structures – same function yet different structure – Ex. Bee’s wing and bird’s wing Vestigial Structures – little or no function Similarities in Early Development The same groups of embryonic cells develop in the same order and in similar patterns to produce tissues and organs of all vertebrates, producing homologous structures Genetics and Molecular Biology DNA and homologous molecules provide evidence of common descent Genetic code almost identical in all living things Testing Natural Selection Darwin’s hypothesis Peter and Rosemary Grant – Beak size and shape must have enough heritable variation – Beak size and shape must produce differences in fitness Tested on medium sized ground finch Grants documented data that natural selection takes place in wild finch populations frequently, and sometimes rapidly Grant’s Research Recap of Darwin •Evolution happens slowly over a length of time. •All organisms differ and some of this variation is inherited. •Organisms compete for resources. •Survival of the Fittest •Over time, natural selection causes changes in species. •Species have descended with modification. •All organisms are connected into a tree of life by common descent.