BIO 4 Macroevolution.txt - BIO153: Lecture 4 Macroevolution...

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1 BIO153: Lecture 4 Macroevolution January 14, 2009 Macroevolution = evolution at or above species level “Macroevolution means evolution on the grand scale, and it is mainly studied in the fossil record. It is contrasted with microevolution, the study of evolution over short time periods, such as that of a human lifetime or less. Microevolution therefore refers to changes in gene frequency within a population . .. Macroevolutionary events are more likely to take millions, probably tens of millions of years. Macroevolution refers to things like the trends in horse evolution described by Simpson, and occurring over tens of millions of years, or the origin of major groups, or mass extinctions, or the Cambrian explosion described by Conway Morris. Speciation is the traditional dividing line between micro- and macroevolution.” Mark Ridley, 1997 EVOLUTION Oxford University Press, Oxford UK Macroevolution often entails major morphological changes – how do they occur? Completely new features are rare – most “new” structures are modifications of existing features e.g. mammalian inner ear arose from bones present in the jaw of reptile ancestors e.g. tetrapod limb : modified functions arise from existing structures (flying, running, burrowing, etc.) Transformation of characters in macroevolution: Changes in: size shape position association with other parts differentiation (complexity)
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2 Example: serially homologous elements -- repeated elements based on the same developmental plan (e.g. petals, ribs, vertebrae, body segments…) These may evolve in number, position, or differentiation:
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BIO 4 Macroevolution.txt - BIO153: Lecture 4 Macroevolution...

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