Wallace began investigating spiritualism in the summer of 1865, possibly at the urging of his older sister Fanny Sims, who had been involved with it for some time. After reviewing the literature on the topic and attempting to test the phenomena he witnessed at séances, he came to accept that the belief was connected to a natural reality. For the rest of his life, he remained convinced that at least some séance phenomena were genuine, no matter how many accusations of fraud sceptics made or how much evidence of trickery was produced. Historians and biographers have disagreed about which factors most influenced his adoption of spiritualism. It has been suggested by one biographer that the emotional shock he had received a few months earlier, when his first fiancée broke their engagement, contributed to his receptiveness to spiritualism. Other scholars have preferred to emphasise instead Wallace's desire to find rational and scientific explanations for all phenomena, both material and non-material, of the natural world and of human society.