I want to know the answer to the following question:
Which book was Darwin working on when he received a package from Wallace?
All the background I'm provided with is that "Darwin was hard at work on his "big book" on Natural Selection, when on 18 June 1858 he received a parcel from Wallace, who stayed on the Maluku Islands (Ternate and Gilolo).". Is that enough to answer the question?
Answer: yes