code: public boolean shouldTerminate(PopulationData<?> populationData)
      {
          if (natural)
          {
              // If we're using "natural" fitness scores, higher values are better.
              return populationData.getBestCandidateFitness() >= targetFitness;
          }
          else
          {
              // If we're using "non-natural" fitness scores, lower values are better.
              return populationData.getBestCandidateFitness() <= targetFitness;
          }
      }
docs: {@inheritDoc}