Whilst searching for something on Charles Smith's Wallace Page website, which contains transcripts of all of Wallace's published writings, I came across the following short article, which had originally been printed in The Argus (Melbourne, Australia) no. 30928: 4c on the 15th October 1945:
"What is Wrong with the World?"
On the last birthday of the late Dr. Alfred Russel Wallace, who died in 1913, I asked him the following question: "From the vantage ground of 91 years, and as the co-discoverer with Charles Darwin of the theory of natural selection, what is wrong with the world?" He instantly answered: "That man's scientific discoveries have outstripped his moral development."
As I left his couch he added: "If I could stumble upon the way to release and control atomic energy I would die with the secret. Man at his present stage of moral character ought not to be entrusted with any more power: he will only destroy himself by it."
-- Sir James Marchant, social writer and worker.
The author, Sir James Marchant (1867-1956) was a philanthropist and writer who was a friend of Wallace's. In 1916 he published a 2 volume book entitled Alfred Russel Wallace; Letters and Reminiscences (Cassell and Co., 507 pp.).
Forgive my lack of knowledge about the history of physics, but how did Wallace know about atomic energy - was this something which was well known in 1913, perhaps as a result of Einstein's work? Comments are welcome below!
See the version from which I took the above text, plus two other similar versions of Marchant's reminiscence about Wallace here.