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Chapter 10

BIOLOGY 1M03 Chapter 10: Chapter 10

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McMaster University
Ben Evans

Chapter 10: From Tree Shrew to Ape  During the Permian and early Triassic periods, much of the world’s fauna was dominated by therapsids, a diverse group of reptiles that possessed traits such as being warm-blooded and covered with hair that linked them to mammals that evolved later  At the end of the Triassic, most therapsid groups disappeared and dinosaurs radiated to fill all of the niches for large, terrestrial animals  One therapsid lineage evolved and diversified  These early mammals were probably mouse-sized, nocturnal creatures that fed mainly on seeds and insects  They had internal fertilization, but still laid eggs  By the end of the Mesozoic era, placental and marsupial mammals that bore live young had evolved  With extinction of dinosaurs at the beginning of the next era (Cenozoic) came the radiation of mammals  According to Darwin’s theory, complex adaptations are assembled gradually, each step favoured by natural selection  Modern humans have many complex adaptations, like grasping hands, bipedal locomotion, toolmaking abilities, language and large-scale cooperation Continental Drift and Climate Change  To understand the evolution of our species, it is important to understand the geological, climatic and biological conditions under which these evolutionary changes occurred  Evolution produces adaptation, but what is adaptive in one environment may not be adaptive in another environment o If the environment remained the same over the course of human evolution, then the kinds of evolutionary changes observed in the hominin fossil record would have to be seen as steady improvements in perfection of human adaptations o But if environment varied through time, evolution would have to track a moving target  One factor that contributed to change in the world is the movement of continents or continental drift  About 200mya, all of the land making up the present-day continents was joined together in a single, huge landmass called Pangaea  About 125 mya, Pangaea began to
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