In a genetic algorithm, when selecting members for crossover using roulette-wheel selection method, does the population first need to be sorted by fitness rank?

The possibilities seem to be:

  1. sort population first by ascending fitness
  2. sort population by descending fitness
  3. don't sort population & let the roulette ball fall where it may..

I'm thinking that sorting either way may have no effect - a pebble landing at random on a wheel containing different sized (by fitness) slices will have exactly the same outcome chance whether the larger slices are grouped together or not. But I'm not 100% convinced.

What do you think?

The need to do a sort every generation affects the speed of the algorithm too, so I'd prefer not to (I would do a sort if using elitism, but I'm not in this case). Thanks if you know, as I cannot find a definitive answer via google etc..

genetic-algorithm roulette-wheel-selection
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