More information about the portrait of Wallace in the National Portrait Gallery is contained in a document typed by Wallace's son William which is in the Natural History Museum library (finding number WP16/2/41). It reads as follows:-
Portrait of Dr Alfred Russel Wallace
now in the National Portrait Gallery [this sentence written later in pencil]
The painting represents Dr Wallace as he appeared soon after his return from his Eastern travels...The photograph from which this painting was done was almost certainly taken by Wallace's brother-in-law, Thomas Sims, a professional photographer. My mother's recollection of the history of this particular portrait was that it was painted on a photograph for Mr Sim's possession till his death and was recently purchased from the lady into whose possession it passed, by Mrs. Wallace. It was probably painted between the years 1863 and 1866. My mother spoke of it as a good likness of him at the time of his marriage in 1866.
The medallion was done my [sic] Mr. Albert Bruce-Joy from models made from life a year or two previous to the date of the cast, viz. 1906. While Mr. Bruce-Joy was at work on the portrait a fire occurred at his studio which destroyed his work on the medallion. I am not sure whether he found it necessary to make further studies from life, but the completion of the portrait was delayed, I believe, a year or more. Mr. Bruce-Joy could of course give more accurate information. A replica of this medallion was exhibited in the Royal Academy, but I cannot state the year. It may have been on a smaller scale. The two portraits are now the joint possession of Miss Wallace and myself.