BIOL321 Lecture Notes - Lecture 4: Mosaic Evolution, Radiometric Dating, Lightning

• School: University of Alberta
• Department: Biology (Biological Sciences)
• Course: BIOL321
• Professor: Heather Proctor

Document Summary

Pattern 2: geographically restricted clades distributions of many taxa make no sense unless they are viewed as descendents from an originally geographically restricted common ancestor. Examples are lemurs in madagascar and many groups of marsupials in australia. Homoplasy can include reversals to old states, what is old and what is new is not always obvious! Example: most salamanders have aquatic larvae except one group, without a tree, or genetic data, it"s almost impossible to tell if it"s a reversal, or if having terrestrial larvae happened more recently. It was once argued that once a complex character state had been lost, it was very unlikely to re- evolve (dollo"s law) however this is not widely believed today as there are many exceptions. Most people today argue that the developmental pathways for the traits are still there, just that the on/off mechanisms for the presence of these traits must be re-evolved. Pattern 4: variation in rates of character evolution.