The International Center for the Improvement of Maize and Wheat stores 123,000 wheat seed samples and 17,000 corn seed samples. Thousand of the varieties were created by farmers over the centuries through plant selection. Cows range from fat, slow European Holstein milk cows to sleek hardy Brahma beef cattle that were adapted to thrive in tropical climes. These large mammals were killed off by invading human hunters at the end of the last Ice Age and, as a consequence, the plants natural ranges were severely reduced. Some were even perhaps heading toward extinction.
Humans also can aim directly at restoring species.
The American Chestnut Foundation plans to bring back the American chestnut, which was devastated by blight in the early part of the 20 th century. The foundation has endowed the American chestnuts with blight resistance by crossbreeding it with Chinese chestnuts. The foundation hopes to begin restoring the new-old American chestnut to Appalachian forests in 2012. More controversially, humanity also enriches ecosystems by moving new species into new regions of the globe. As Cornell University biologist David Pimentel points out, some 50,000 non-native species now reside in the United States.