Chapter 25 The History of Life 2nd Half of Ch Macroevolution is the major change in life above the species level in earth s history The evolution of new major groups and new structures Extinction and adaptive radiation Revealed in the fossil record Fig 25 4 Origin of new groups amphibians birds squirrels Starts with microevolution which leads to speciation 1 new species is the ancestor of the entire group o Ch 22 elephant family example Adaptive Radiation Diversification from an ancestor o New adaptation of ancestral species lead to expansion of the range o Moving into new areas and habitats promoted more speciation Historically adaptive radiation followed after mass extinctions o Opened new areas and resources Also seen in isolated island groups Many branches were lost over time as environments changed horses Origin of new features By incremental evolution o Each step is better adapted for the same use eyes in mollusks Exaptation occurs when an existing adaptation is modified for a different use o Ex Hair insulation led to porcupine quills o Ex Hinge bones in mammalian ancestors become ear bones 25 6 and CH34 o Ex Feathers insulation led to flight Effects of developmental genes evodevo o Their function is to turn genes on and off at precise times and places during development o Homeotic genes are genes that control the placement of body parts Mutation in one or two of the genes causes massive effects 18 20 Hox genes 25 23 24 Heterochrony is the change in the rate or timing of developmental events o May produce new final shapes chimps and humans o May produce a sexually mature adult with juvenile features PAEDOMORPHIS salamander with gills
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