Perhaps you are one of the readers of this book with a specific question in mind: ‘looks interesting…but does it help to answer how I should model my own problem concerning my favourite snail/bird/mite/ungulate/whatnot’? And perhaps you have already seen the light and decided that a population genetic approach will work brilliantly, or perhaps dynamic optimization, or some other technique introduced so far. But perhaps I am being overoptimistic here. Quite likely, there are still too many factors floating around in your head: the organism may be beautiful to work with, but to model, oh no … it does not only X but also Y and Z, and F and G and K surely influence what it should be doing, besides, the weather keeps changing and this drastically changes reproductive success from year to year, so how can one ever hope to summarize the long-term fitness prospects in a neat simple equation…

Well, there are two answers. One is simply to read Ch. 1 again and think about what is the essence of your problem. Maybe you should start off by examining one question at a time, rather than trying to answer everything simultaneously. But, there is also answer number two: if you still cannot write down an equation despite being clear-headed about what the question is, and you not being too greedy about how many factors to allow to influence fitness…then you may want to resort to simulations.