Derivatives are set to Zero to determine local optima. Keep in mind that solving system of non-linear equations is most difficult task in numerical computation. Hop on the function and go on the direction of greatest descent. These are just as good as rolling the dice. From all the techniques, calculus-based techniques do the best in certain problem domains and Enumerative method does a good job when the search space is small.
Random searches perform almost the same across the board.
GAs search from a population of points. They don't require any extraneous information. GAs use probabilistic transition rules, not deterministic rules. To solve any problem using GA, we should consider the following. I would be adding some more preliminary information in future.