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Adaptation and Evolution of Populations

Natural selection favors certain traits in a population so that the organism adapts to its environment; changes in the genes over time is evolution.

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When Continents Collide

When Continents Collide

When the Isthmus of Panama rose from the sea to connect South America to North America the two sets of animals came into competition. Who would win?

Amazing But True!

  • North America and South America were separate. However, their animals, especially mammals, were very similar.
  • About 2.5 million years ago, the volcanic Isthmus of Panama rose to connect the two continents through Central America. There was no competition between the two sets of animals.
  • North American mammals prevailed in most cases.
  • The Great American Interchange explains the migration of North American animals to South America and South American animals to North America. This migration occured in the Piancenzian age, approximately three million years ago.

    Ancestors of Nearctic (red) and Neotropic (green) species wandered via two-way migrations in the Cenozoic period (before the interchange)


Show What You Know

With the link below, learn more about the great American interchange. Then answer the following questions.

  1. When North and South America were separate what was going on with animals on both continents and why?
  2. What was the biggest difference between North American and South American mammals?
  3. Why did there need to be competition between the two sets of animals when the continents joined? Why does the author say that neither set had an obvious advantage?
  4. What is the hypothesis that scientists have for why the North American mammals did better than the South American mammals?
  5. Why are humans an exception to the rule of northern animals doing better than southern ones?

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