Concept of species essentialist
The essentialist concept of species is based on the idea that that members of the same species objectively share a certain inner quality, essence, that sets them apart from members of other species. According to essentialists, the number of species or organisms and boundaries between these species is unambiguously determined beforehand, similarly as, for example, the number and shape of Platonic bodies are determined beforehand. Essentialists explain the existence of species internal variability as being a consequence of a different degree or quality of expression of this essence, where this unequal degree of expression has its origin in unforeseeable random effects of the surroundings on a particular organism. Philosophically, the essentialist concept is based in Plato’s world of ideas (where Plato’s own approach to classification of objects was based on other principles and it is improbable that he would consider himself an essentialist in the modern definition of this term). Similarly as transitions between triangle and rhomboids cannot exist in an ideal world, according to essentialists there cannot exist transitions between individual species. However, transitions between species can, of course, exist in our real (and imperfect) world. Here, however, it is frequently useful to differentiate between the essentialist and nonessentialist explanation of the difference between species (or between anything at all). For example, there are certainly several ways in which clocks can be formed. Simultaneously, it is hard to image a transitory type between pendulum clocks and crystal clocks – the differences are essential. In contrast, there can be quite continuous transitions between detergent powders and the fact that only a certain number of kinds of detergent powders are available in stores is not a consequence of the fact that transition kinds couldn’t be mixed or that transition forms would wash less efficiently. This is given by “external factors”, the business strategy of the manufacturer or seller or the laws of competition amongst individual market entities.
It is not probable that the essential concept of a species, at least in its original sense, would be very useful for description and explanation of the phenomenon of the existence of species in live nature. Species are not crystals or geometric objects, but products of a unique series of historical events, whether this series of historical events is considered to consist of biological evolution or biblical creation. This means that this development into the present-day form was affected not only by deterministic processes that necessarily followed from the properties of the particular system, but also, to a substantial degree, by chance. To assume under these conditions that the individual species should differ in a certain special category of properties, i.e. essential properties, is perhaps not completely naive, but is certainly very impractical. It is, of course, possible and, in fact, quite probable that any two species will differ from one another in a specific property, whether this is a particular biochemical or physiological property of their members or a certain aspect of their position in the ecosystem. However, this property is “essential” only in that it differentiates the two particular species. It is more than questionable whether the concept of a species based on “essential” properties defined in this way could be included in the category of an essential concept of species.