Darwin's discussion of bird species on the Galapagos islands relates to natural selection because the finches all have a recent common ancestor, but they evolved on different islands with different types of food, so the birds that weren't fit enough to survive the island conditions died, and the ones that did were "naturally selected."
Explanation:
The finches all have a recent common ancestor but they evolved on different islands where different types of food are available. During his visit to the islands, Darwin noted that the unique creatures were similar from island to island, but perfectly adapted to their environments which led him to ponder the origin of the islands' inhabitants. Among those that struck Darwin so greatly were the finches that are now named in his honor.
