“How can that be explained as a part of progress?” asked Marian.
Virginia, with her usual misconception on this subject, said that disease helped us forward because through it scientists came to know and understand many things about life. Henry, still more off the track, said that disease led to a knowledge of medicine.
“Henry’s idea,” I answered, “we cannot consider, because, of course, the only virtue of medical skill is that it cures disease, and if there were not disease we would not need medical progress. But Virginia’s idea is true in a certain sense. It is quite true that disease impelled people to use the microscope, to discover themselves physically, to learn of the infinitude of minute creatures in the universe; and so it led to a larger knowledge of life, because the infinitely little makes our world just as vast as the infinitely big. But this only shows that we made progress out of disease, as we make progress out of all things, because the will of life, the will to go forward, is within us. It does not show how disease itself can be the result or price of progress. That is a difficult question, but I seem to see it clearly, and I will try to explain it to you. None of you, except perhaps Virginia and Alfred, have a clear idea of evolution, and I would like to spend one meeting in explaining it, because it is so essential. Don’t you think so?”
“But I can’t go into this question of disease without explaining something of evolution to you now. I will try to make it clear: Each individual is different. As animals progressed and went forward, those parts which were newest were also more unstable, because they were ready to change more. These parts were most apt to become diseased, or, rather, weakened, because progress might be in any direction, and had to feel its way.” It was difficult for me to explain this to the children, who were so utterly unprepared, and I said much more. Even so, I don’t think Marian and Ruth understood it thoroughly, and I shall have to repeat it when we speak of evolution. I said I did not believe the germs of disease ever entered any part unless that part were weakened or imperfect. I said: “Take as an example the human brain. Suppose that two children were born with brains slightly different from others. One might turn out to be a genius, and the other to be eccentric and even insane, because progress feels its way in all directions. So disease, coming to the new unstable parts, would be the necessary cost of progress.”