Once you have identified your key interest area, start narrowing it down to one clear problem. It is an important stage, because if you fail to formulate a clear definite topic, you will never manage to compress all your passion into a necessary amount of words and organize your writing in coherent paragraphs without being overwhelmed with emotions. Imagine, you love dancing and decide to write about it. Immediately a whole hurricane of ideas is stirred in your head: types of dancing, ballet, hip-hop, classical dance, benefits, training techniques, etc.
Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called " artificial selection "; in his early manuscripts he referred to a "Nature" which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: "I am convinced that Natural Selection has been the main but not exclusive means of modification."  In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term "Natural Selection", preferring the term "Natural Preservation".