@Override
		public String toString() {
			return super.toString() +
				"+---------------------------------------------------------------------------+\n" +
				"|  Population statistics                                                    |\n" +
				"+---------------------------------------------------------------------------+\n" +
				format(cpattern, "Age:", p(_age)) +
				format(cpattern, "Fitness:", "") +
				format(spattern, "min  =", d(_fitness.min())) +
				format(spattern, "max  =", d(_fitness.max())) +
				format(spattern, "mean =", d(_fitness.mean())) +
				format(spattern, "var  =", d(_fitness.variance())) +
				format(spattern, "std  =", d(sqrt(_fitness.variance()))) +
				"+---------------------------------------------------------------------------+";
		}
Return the minimal and maximal fitness.

@return minimal and maximal fitness
jenetics/src/main/java/io/jenetics/engine/EvolutionStatistics.java