Overview: Niles Eldredge gives a historical overview of scientists' thinking on the process of speciation, along with modern perspectives on this issue. This article appears at ActionBioscience.org. Author/Source: ActionBioscience.org Grade level: 9-12 Time: 30 minutes Teaching tips: This article is very advanced and may be appropriate for AP biology. Student learning on this topic may be enhanced by supporting resources and classroom discussion. Concepts: Biological evolution accounts for diversity over long periods of time. Present-day species evolved from earlier species; the relatedness of organisms is the result of common ancestry. Geological change and biological evolution are linked. Tectonic plate movement has affected the evolution and distribution of living things. Rates of extinction vary. Speciation is the splitting of one ancestral lineage into two or more descendent lineages. Speciation requires reproductive isolation. Occupying new environments can provide new selection pressures and new opportunities, leading to speciation. Scientists can test ideas about events and processes long past, very distant, and not directly observable. Scientific knowledge is open to question and revision as we come up with new ideas and discover new evidence. Accepted scientific theories are not tenuous; they must survive rigorous testing and be supported by multiple lines of evidence to be accepted. Rates of evolution vary. Rates of speciation vary. Speciation is often the result of geographic isolation. Teacher background: Speciation

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