 The above survey of candidate unifying features is far from exhaustive. But the result is clear enough. Species vary in their unifying processes and ontological structure. Furthermore, many features that biologists and philosophers highlight as unique to species occur in many higher taxa as well. Given this survey, what position should we adopt concerning the nature of species? There are several options. According to one option we should keep looking for the unifying feature of species. This is the option favored by some monists (Sober 1984). Contemporary biology may not have discovered the unifying feature of species, but that does not mean that biology will not find such a feature in the future. To give up the search for the unifying nature of species would be too hasty.