Speculations about the development of life are very fascinating. I hold very strongly to belief in the survival of the fittest. Accepting this theory, you can explain most of the apparent inconsistencies that exist in the world. But I must admit that there is at least a possibility that genera are not changed by environment, time or circumstances. Perhaps they exist until they become unfit, when they vanish. The genus may remain in existence as a permanency till it ceases to become fit to survive, but the species most certainly alters. The only point in dispute is, therefore: do genera become altered by environment, etc.? Or do they exist unaltered till they become unfit, when they just vanish from this sublunary scene? However this may be, the broad principle of natural selection seems to me to be unshakably established. _May 20th, 1917._ I was absolutely taken aback by the news of Felix Cohn's[18] death. It seems almost incredible to me, even at this moment. It was only a few days ago that we met out here. He had then been "over the top" and was in high spirits. He was a sincere fellow and played his part like a man. I do take off my hat to the Infantry. No one in England realises what we all owe to them; marvellous men they are. How they endure what they do, Heaven only knows. If you see Mr. Cohn, please express to him my deepest sympathy, or rather, send me his address and I will write to him. [Footnote 18: Second Lieutenant Felix A. Cohn, East Surrey Regiment. Born, August 31st, 1896. Killed, May 3rd, 1917. Was in the Modern Sixth at Dulwich with Paul Jones. Son of Mr. August Cohn, barrister.] We of the Tank Corps are having a pleasant and peaceful time in billets these days. Nature hereabouts is beginning to put on her best dress. It is _some_ contrast between the vivid green foliage that one sees about here and the blasted trees and shell-shattered areas of the fighting zone. Only one thing indicating the living force of nature did I remark in that dreary countryside. This was the piping of a few birds now and again in the most unlikely places. Bar that, the battle zone is a blasted area, where the only difference between the seasons is noted by a change of temperature and the transformation of mud into dust. Meanwhile, I am having a very good time in billets; but I am looking forward eagerly to a real scrap with the Boche. Thanks so much for the "Perfect Wagnerite." It is a treat to read about the "Ring" once more. I would give much to be able to hear it again. TO HIS BROTHER. _May 25th, 1917._