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Darwin and Natural Selection Evolution • The change in a species over time. • Proposed by Charles Darwin • Natural selection is the process by which organisms that are best suited to their environment survive and pass their genetic traits on to their offspring. • “Survival of the Fittest” (fitness determined by number of offspring produced) Some Ideas That Had to be Changed • Belief that the Earth was young – Most Europeans in Darwin’s day believed that Earth and all its forms of life had been created only a few thousand years ago – Too little time for evolution • Wrong Ideas – Lamark’s Theory of Evolution • Use and Disuse • Inheritance of Acquired Traits How Did Giraffes Get Long Necks? Stabilizing Selection Directional Selection Disruptive Solution Summary of Darwin’s Theory • Individual organisms in nature differ from another. Some of this variation is inherited. • Organisms in nature produce more offspring than can survive, and many of those that survive do not reproduce. • More organisms are produced than can survive, members of each species must compete for limited resources. • Because each organism is unique, each has different advantages and disadvantages in the struggle for existence. • Individuals best suited to their environment survive and reproduce most successfully. The characteristics that make them best suited to their environment are passed on to offspring. Individuals whose characteristics are not as well suited to their environment die or leave fewer offspring. • Species change over time. Over long periods, natural selection causes changes in the characteristics of a species, such as in size and form. New species arise, and other species disappear. • Species alive today have descended with modifications from species that lived in the past. • All organisms on Earth are united into a single tree of life by common descent. Evidence For Evolution • Adaptations – evolution of a structure, behavior, or internal process that enables an organism to respond to stimuli and better survive in an environment • (e.g. mole-rats on pp. 404-405) • Can you name some examples? Fossil Record Homologous Body Structures Analogous Structures Vestigial Organs Similarities in Early Development Geographic Distribution of Living Species Evidence For Evolution • • • • • • • The Fossil Record Homologous Body Structures Analogous Body Structures Vestigial Organs Similarities in Early Development Geographic Distribution of Living Species Biochemistry Evolution on Different Scales • Evolution that occurs within the species level is called microevolution. It results from genetic variation and natural selection within a population of organisms. • Macroevolution is evolution that occurs between different species. It focuses on how groups of organisms change (i.e., the splitting of a species into two species). Summary of Darwin’s Theory • • • • • Individual organisms in nature differ from one another. Some of this variation is inherited. Organisms in nature produce more offspring than can survive, and many of those that survive do not reproduce. Because more organisms are produced than can survive, members of each species must compete for limited resources. Because each organism is unique, each has different advantages and disadvantages in the struggle for existence. All organisms on Earth are united into a single tree of life by common descent. • Individuals best suited to their environment survive and reproduce most successfully. The characteristics that make them best suited to their environment are passed on to offspring. Individuals whose characteristics are not as well suited to their environment die or leave fewer offspring. • Species change over time. Over long periods, natural selection causes changes in the characteristics of a species, such as in size and form. New species arise, and other species disappear. • Species alive today have descended with modifications from species that lived in the past.