River barrier hypothesis

The river barrier hypothesis is a hypothesis that partially explains the high species diversity of the Amazon Basin, first presented by Alfred Russel Wallace in an 1852 paper on the monkeys of the Amazon. It argues that the formation and movement of the Amazon River and some of its tributaries created a barrier to wildlife movement substantial enough to bring about allopatric speciation; populations divided by the river faced different selection pressures and genetic drift and diverged into separate species. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/