GE CLST 70B Lecture Notes - Lecture 12: Runaway Greenhouse Effect, Marine Regression, Paraphyly
24 Feb 2017
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Darwin viewed most change occurring within lineages. Anagenetic change: continuous change within a lineage. Cladogenetic change: most change associated with speciation events. Eldridge and gould publish an influential paper in 1972, suggesting that the majority of phenotype change was associated with speciation (cladogenetic) Based on a model of speciation which suggested phenotypic change might be rapid in small peripheral populations and would happen @ the same time as speciation. Phyletic gradualism model: lineages gradually change and evolve over time: little change associated with speciation other than reproductive isolation. Punctuated equilibrium model: most change happens rapidly in peripheral populations that branch off from main populations that are in equilibrium: most change is associated with speciation, there is stasis within lineages (little anagenetic change) There is still debate about which model is correct. Some studies show punctuated equilibrium: lake turkana mollusks. Some studies show gradual evolution: trilobites, bison teeth.
