More or less at random, I started reading Michael Blastand's great book "The Hidden Half". I am quite sure, if somehow I re-ran the last year starting at the same point, I would not have encountered this book. Why? Read on. You may have heard of the "butterfly effect". What you may not have heard is that it covers almost everything, not just weather. The way genes are expressed have feedback loops and these loops include the environment. Feedback loops are the source of the phenomenon of chaos, just as they are in predicting the weather. There is no reason why two individuals with the same genotype will not, due to chaotic gene expression, reveal radically different phenotypes. Chaos is generally ignored - for example, in Michael's great book "The Hidden Half". Loops like this are mentioned, for example, Walter Isaacson''s "The Code Breaker". In the case of Blastland's crayfish, any tiny variation would produce larger and larg