Wallace was a very far ways down to same path Darwin trod, and for much the same reasons; he had consulted with Darwin, and he was very impressed with Darwin's excruciatingly detailed efforts, and was a generous and gentle soul. He happily shared the pre-publication early exposures of the theory as the junior of the two, recognizing that Darwin's efforts far outstripped his in detail and scope, if not speed to market.
Looking at relative publication dates, it would be fair to say the Wallace could have stolen a great deal of Darwin's thunder, if he had simply published what he had, when he had intended to. That he chose not to commends him to me very much in an age already heating up with scientific competitiveness.
However, be that as it may, that in no way makes Darwin's work plagarism, or anything even remotely resembling plagarism, nest paws?