lecture20F06

lecture20F06 - Lecture 20: Macroevolution Readings: Ch....

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Lecture 20: Macroevolution Two explanations for macroevolution gradualism, punctuationalism Gradualism continental drift analogy; gradual changes in DNA sequences; accumulation of large differences in real time in viruses; the molecular clock hypothesis; morphological stages as gradual steps Readings: Ch. 25.3 (but many Figures used from other chapters) “Punctuationalism” the punctuated equilibrium model, with or without speciation; Can small genetic changes produce large morphological effects? allometry; heterochrony; homeotic mutations; Hox genes Evolution is not goal oriented
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Charles Darwin’s explanations for macroevolution: gradualism His proposal is that macroevolution is just the accumulation of the effects of microevolution. This is essentially in part what Darwin meant by “descent with modification”. We now have a better appreciation that a large fraction of evolutionary change may accumulate in speciation events, if the punctuation model is correct.
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An analogy to show how small changes can gradually accumulate to produce huge differences: continental drift . Continental drift, which is the movement of the continents over time as huge crustal plates on the surface of the earth move with respect to each other. See Figs. 26.18-20. Plates can separate, driving speciation, or slide under one another (as Darwin in effect saw), raising mountains.
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Fig. 26.18. The crustal plates and their patterns of movement. Note that South American and Africa were once one continent, now divided.
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We can actually see the gradual movement of plates in almost real time now. Movement of the “big island” of Hawaii, as measured using GPS (Geographic Positioning System) From the Jet Propulsion Laboratory (http://sideshow.jpl.nasa.go v/mbh/series.html )
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The point: small, gradual changes add up to a lot of plate movement given a few million years.
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lecture20F06 - Lecture 20: Macroevolution Readings: Ch....

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