During a trip to the Galapagos Islands, which observation led Charles Darwin to suspect that organisms change over time?

Darwin noticed that Galapagos finches were similar to finches on the South American mainland, yet they differed enough to be distinct species. This suggested that island species may have descended from mainland ancestors and changed over time. Differences in beak size and shape among island finches were also important, but choice A best captures the observation linking them to change over time.

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