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This edition: Macroevolution

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Episode Details

Who is related to whom? How do species evolve? What has happened in geological time? This lesson focuses on macroevolution and the processes that explain it. It begins on location at a paleontological site in the Big Horn Basin, Wyoming, where scientists are recording mammalian evolution in the first 10 million years after the Cretaceous/Tertiary boundary extinction. A key question of macroevolution is, “What distinguishes a species?” This leads to taxonomy and discussion of the two main approaches to classification: evolutionary systematics and cladistics. Examples are given of homologies and analogies, and ancestral and derived traits, keys to classifying by these different approaches. Cladistics focuses only on derived traits. In the second segment, two different species concepts are mentioned—the biological species concept, which is the most commonly used definition, and the ecological species concept, which places emphasis on niche occupation and natural selection. The difficulty of recognizing a fossil species is explained by anthropologists Alfred Rosenberg and Jonathan Bloch. In the third segment, the immense time span involved with macroevolution is examined, continental drift and its effects are explained, and the characteristics of mammals are illustrated. The video returns to the paleontological site in the Big Horn Basin, where Bloch is seen excavating.