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15-1 The Puzzle of Life's Diversity Copyright Pearson Prentice Hall What is evolution? Biological evolution refers to the changes in the genetic makeup of a population of interbreeding organisms of the same species that occur over time. These genetic changes are the result of mutations in the DNA sequence of the organism, which are passed from one generation to the next. Populations change over time. The slow , gradual change in a population of organisms over time. Evolution Evolution is the process by which modern organisms have descended from ancient organisms. A scientific theory is a testable explanation of phenomena that have occurred in the natural world. It can’t be proven right, only supported. It can be proven wrong Know the difference: The fact of evolution. The Theory of Natural Selection. Copyright Pearson Prentice Hall Charles Darwin Born Feb. 12, 1809 Joined Crew of HMS Beagle, 1831 Naturalist 5 Year Voyage around world Avid Collector of Flora & Fauna Astounded By Variety of Life Voyage of the Beagle In 1831, Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world. Copyright Pearson Prentice Hall During his travels, Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time. That hypothesis has become the theory of evolution (aka theory of natural selection). Copyright Pearson Prentice Hall Darwin's Observations He observed many plants and animals were well suited to the environments they inhabited. He was impressed by the ways in which organisms survived and produced offspring. Darwin was puzzled by where different species lived and did not live. Copyright Pearson Prentice Hall 8 Living Organisms and Fossils Darwin collected the preserved remains of ancient organisms, called fossils. Some of those fossils resembled organisms that were still alive. Others looked completely unlike any creature he had ever seen. Copyright Pearson Prentice Hall The Galápagos Islands Darwin observed that the Galápagos Islands were close together but had very different climates. Copyright Pearson Prentice Hall The Journey Home Darwin wondered if animals living on different islands had once been members of the same species. These separate species would have evolved from an original South American ancestor species. Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Copyright Pearson Prentice Hall Inherited Variation and Artificial Selection Due to genes crossing-over in the process of meiosis (formation of gametes), all organisms will inherit variation. That is why no two organisms (except for identical twins) look exactly alike. However, when humans interfere, they can decide which individuals to breed. They will chose to breed the individuals with the desired characteristics. Artificial selection is the selection by humans for breeding of useful traits from the natural variation among different organisms. Results in “breeds” Evolution by Natural Selection Darwin compared processes in nature to artificial selection. By doing so, he developed a scientific hypothesis to explain how evolution occurs. Copyright Pearson Prentice Hall The Struggle for Existence Darwin realized that high birth rates and a shortage of life's basic needs would force organisms to compete for resources. Copyright Pearson Prentice Hall Think about it… How is natural selection related to a species' fitness? Copyright Pearson Prentice Hall Survival of the Fittest The ability of an individual to survive and reproduce in its specific environment is fitness. Darwin proposed that fitness is the result of adaptations. An adaptation is any inherited characteristic that increases an organism's chance of survival. Copyright Pearson Prentice Hall Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as natural selection. In natural selection, the traits being selected contribute to an organism's fitness (survival and reproduction) in its environment. Copyright Pearson Prentice Hall Evolution by Natural Selection The organisms that survive long enough to reproduce because of certain traits then pass on those traits that helped them survive. These changes increase a species' fitness in its environment. Over time, natural selection results in changes in the inherited characteristics of a population. This process is known as evolution. Copyright Pearson Prentice Hall Principles of Natural Selection Descent With Modification Natural selection produces organisms that have different structures, establish different niches, or occupy different habitats. Each living species has descended, with changes, from other species over time. Darwin referred to this principle as descent with modification. Copyright Pearson Prentice Hall Evidence of Evolution Darwin argued that living things have been evolving on Earth for millions of years. Evidence for evolution include: •the fossil record •geographical distribution •homologous structures •similarities in early development, or embryology. •DNA Sequences Copyright Pearson Prentice Hall The Fossil Record Darwin saw fossils as a record of the history of life on Earth. By comparing fossils from older rock layers with fossils from younger layers, scientists could document that life on Earth has changed over time. Copyright Pearson Prentice Hall Geographical Distribution Similar, but unrelated species develop similar characteristics due to having to cope with similar environmental pressures. Here, the beaver and the capybara are similar species that inhabit similar environments of North America and South America. The South American coypu also shares many characteristics with the North American muskrat. Copyright Pearson Prentice Hall Homologous Body Structures Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures. Examples: Copyright Pearson Prentice Hall Homologous Structures The limbs of these four modern vertebrates are homologous structures. They provide evidence of a common ancestor whose bones may have resembled those of the ancient fish shown here. Notice that the same colors are used to show related structures. Homologous structures are one type of evidence for the evolution of living things. Homologous structures are one type of evidence for the evolution of living things. Turtle Alligator Bird Ancient, lobefinned fish Copyright Pearson Prentice Hall Mammal Structures; Comparing Anatomy Homologous Physical Characteristics Analogous Found in related species May not appear similar at first, but they are closely related. Ex. Forelimbs in humans, cats, and whale. Physical Features Serve same function Do not indicate a shared common ancestor, but they evolved independently. Ex. Wings on insects, bats, and birds. Homologous Structure Analogous Structure Not all homologous structures serve important functions. There are organs in many animals that have no use and are so reduced in size that they are just vestiges, or traces, of homologous organs in other species. These organs are called vestigial organs. Examples: Copyright Pearson Prentice Hall Similarities in Embryology The early stages, or embryos, of many animals with backbones are very similar. The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. Copyright Pearson Prentice Hall DNA Sequences