Darwin observed that tortoises of the nearby islands, although slightly different, belonged to the same species. How might he have known they were the same species?

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Darwin likely knew the tortoises were the same species because he observed that they could interbreed when brought together, which is a common criterion for determining whether organisms belong to the same species. He did not have access to DNA sequence data, and comparing the metabolism of the tortoises would not necessarily provide information about their species classification. Darwin did not move tortoises to a new island to observe changes, as he did not intervene in natural populations in this way.

Darwin Observed That Tortoises of the Nearby Islands, Although Slightly