The breeding of animals is necessary to produce ______. Humans have bred animals and plants for years through the process of ______ in order to
hand-select traits needed in the livestock or produce. In nature, it is not quite so simple. Charles Darwin was a naturalist that proposed the idea of ______. When visiting the Galapagos islands, he discovered there was great ______ between the tortoises on different islands. The different tortoises had specific ______ to survive on the islands that they were found on.