# File lib/ai4r/genetic_algorithm/genetic_algorithm.rb, line 90
      def selection
        @population.sort! { |a, b| b.fitness <=> a.fitness}
        best_fitness = @population[0].fitness
        worst_fitness = @population.last.fitness
        acum_fitness = 0
        if best_fitness-worst_fitness > 0
        @population.each do |chromosome| 
          chromosome.normalized_fitness = (chromosome.fitness - worst_fitness)/(best_fitness-worst_fitness)
          acum_fitness += chromosome.normalized_fitness
        end
        else
          @population.each { |chromosome| chromosome.normalized_fitness = 1}  
        end
        selected_to_breed = []
        ((2*@population_size)/3).times do 
          selected_to_breed << select_random_individual(acum_fitness)
        end
        selected_to_breed
      end