Chapter 24 - Chapter 24 The Origin of Species Chapter 24...

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Chapter 24 - The Origin of Species Chapter 24 The Origin of Species Lecture Outline Overview: That “Mystery of Mysteries” Darwin visited the Galápagos Islands and found them filled with plants and animals that lived nowhere else in the world. o He realized that he was observing newly emerged species on these young islands. Speciation—the origin of new species—is at the focal point of evolutionary theory because the appearance of new species is the source of biological diversity. Microevolution is the study of adaptive change in a population. Macroevolution addresses evolutionary changes above the species level. o It deals with questions such as the appearance of evolutionary novelties (e.g., feathers and flight in birds) that can be used to define higher taxa. Speciation addresses the question of how new species originate and develop through the subdivision and subsequent divergence of gene pools. The fossil record chronicles two patterns of speciation: anagenesis and cladogenesis. Anagenesis, phyletic evolution, is the accumulation of changes associated with the gradual transformation of one species into another. Cladogenesis, branching evolution, is the budding of one or more new species from a parent species. o Only cladogenesis promotes biological diversity by increasing the number of species. Concept 24.1 The biological species concept emphasizes reproductive isolation Species is a Latin word meaning “kind” or “appearance.” o Traditionally, morphological differences have been used to distinguish species. o Today, differences in body function, biochemistry, behavior, and genetic makeup are also used to differentiate species. Are organisms truly divided into the discrete units we called species, or is this classification an arbitrary attempt to impose order on the natural world? In 1942, Ernst Mayr proposed the biological species concept. o A species is defined as a population or group of populations whose members have the potential to breed with each other in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species. o A biological species is the largest set of populations in which genetic exchange is possible and that is genetically isolated from other populations. Species are based on interfertility, not physical similarity. For example, eastern and western meadowlarks have similar shapes and coloration, but differences in song help prevent interbreeding between the two species. In contrast, humans have considerable diversity, but we all belong to the same species because of our capacity to interbreed.
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Prezygotic and postzygotic barriers isolate the gene pools of biological species. Because the distinction between biological species depends on reproductive
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Chapter 24 - Chapter 24 The Origin of Species Chapter 24...

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