Darwin believed that the various species of finches on the galapagos islands came from one common ancestor. he believed they evolved by what?

adaptive radiation 

(the diversification of a group of organisms into forms filling different ecological niches)

He believed they evolved because of he food source. Whether the food was on a tree so they must have long necks or if the food was on the ground, therefore they did not need long necks.

Answergovernment control over all imports and exports;

Light rain because storms had lightning and it started crops on fire or destroyed stuff