A number of concepts of species are concerned with the potential for delimiting species vis-a-vis one another at a single time level. However, especially paleontologists are frequently faced by the problem of how to define the boundaries of species in time or, to be more exact, in the fossil record including samples of organisms over a long period of time. A number of sometimes mutually compatible and, in other cases, incompatible concepts of species attempt to define such delimitations. The evolutionary species concept is the most general concept that encompasses most cases (Simpson 1951). According to this concept, an evolutionary species is a related line, i.e. linear or branching sequences of the population that are related by the ancestor-progeny relationship, which develops separately from other similar lines and which has its specific evolutionary function (role) and specific evolutionary tendencies. This is obviously a phenomenological definition, i.e. a definition that describes the given phenomenon but does not consider the reasons for the existence of distinct species or the mechanisms that keep their members together (in their phenotype). According to this definition, a species is considered to be a group in populations occurring at various places in space and at various moments in time that have the same function in evolution, for example that led to the formation of a new species amongst their members at a certain instant, and that have the same evolutionary tendency, i.e. the phenotype of their members changes in the same way in evolution. At first glance, it may seem that this definition is so general that it can be of little assistance in delimiting species in practice. In this respect, it does not differ much from the typological conception of a species – however, there we are used to its generality and mostly are not even aware of its phenomenological character.
- more or less1836
- not at all2087