“Species are nature’s only objective taxonomic units”

Gould thinks that species are objective. He says populations do “branch from their ancestors, evolving, interbreeding and “maintain common ecological niche” (20).  In addition, there is strong evidence to show that species are “mental abstractions embedded in culture practice or packages in nature” (20). Gould gives examples of the classification method of organisms by people from other cultures, including New Guinea and Tzeltal. These “folk taxonomies” (20) show striking consistency with our more “scientific” Linnaean catalog. Thus, he argued that nature really is divided into discrete species. Gould claimed that most of the time, species stay in steady lineage. Evolution is rather a “rapid transition” than “slow transformation” (26). Our nature is more likely to be “structure and legitimate distinction”. He points out that “species are the units of nature’s morphology” (26).

Gould thinks that higher taxonomic groupings are not objective. He argues that these higher level taxonomic units group actual species in different rankings, though species “neither interbreed nor interact at all.” He admits that these higher taxonomic groups do reflect evolutionary genealogy, but the “way of telling” (Sternly and Griffiths, 187) which species should be grouped into higher taxonomic is not objective. By this he means that there is no objective way to judge whether the grouping is “correct” or not. Gould argues that the grouping of higher taxonomic are often influenced by human decisions, and reflect the culture factor.

Since no one can agree on the “correct” ranking to identify a species or a subspecies, is species ranking really objective?

Although the existence of natural kinds cannot be assured, we cannot conclude that our ranking method in grouping organisms into “species” is objective. Consider this example: Scientists cannot agree on the existence on Higgs boson, so does this mean our method in finding Higgs boson is subjective? Apparently we cannot say the method is subjective. We may not be able to agree on single species concept, but this cannot deny the possibility of the existence of real natural kinds. Thus, this cannot deny the possibility of an objective ranking method that can reflect the natural kinds. Our ranking methods in species are more likely to be objective explorations in the consideration of natural kinds.

Further, as far as our natural observation, organisms are more within discrete structural isolated lineage. So if species does exist, then there should be several methods that at least closely reflect the real natural kinds. Scientists are finding an objective way to approach real natural kinds. In fact, although we have different species ranking methods, most of them rely more on scientific characteristic instead of scientists’ individual preference. As Mishler and Donoghue said, “We ranking criteria could include group size, gap size, geological age, ecological and geographical criteria, degree of intersterility, tradition and possibly others” (Erefesky,674) . All these reflect that our “way of telling” which group is species is scientific and objective. In this sense, the classification of organisms is rather objective than subjective.

Although we have different ranking methods for organisms, these different methods do not necessarily mean that our consideration of ranking species is subjective. According Ereshefsky’s argument on species pluralism, species cannot be defined by monist. He thinks that “the forces of evolution segment” (676) the lineage of life into three kinds of taxonomies, the interbreeding, ecological, and phylogenetic. It is infeasible to find single criteria to fit all three characteristics. Moreover, there is no evidence that a fourth parameter common to all this three types exist.  If Ereshefsky is correct, then we should have multiple ranking methods which take these three approaches be applied in defining species. So the fact that we have multiple ranking methods does not imply our ranking methods are subjective. Instead, multiple ranking methods reflect the multiple parameters of the real taxonomies in natural kinds.

Even if the ranking method of species, as some biologists consider, is purely a production of human mind, can we regard species ranking is subjective? Not necessarily. Consider this possibility: the species concept embedded in the human mind may be an evolution outcome of fitting in the natural world. This means that human developed the species ranking methods during evolution in ranking organisms which helps us to see the invisible natural kinds. These ranking methods help us to distinguish species, assist us to better realize our living environment, which in turn help us to survive. Consequently, our ranking methods of species will reflect the real natural kinds, and it exists outside of our subjective thinking. In this sense, our species ranking can be considered as objective.

As for the ranking methods of higher taxonomies (domain, kingdom, phylum, class, family, order and gene), in my opinion, they are more likely to be subjective than species ranking. Different from species, higher taxonomic units “are collections of species and have no separate existence in nature” (Gould, 20). Species ranking reflects objective distinctions of real natural kinds, but high ranking methods pack up species concept simply for better understanding and practicality.