The pronoun one, in bold in the text, refers to:

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Q1660115 Inglês
The idea of evolution (which is gradual change) was not a new one. The Greeks had thought of it, so Erasmus Darwin, the grandfather of Charles, and also the Frenchman, Lamarck. It is one thing to have an idea; we can all of us guess and sometimes make a lucky guess.  
The pronoun one, in bold in the text, refers to:
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