Principal of Systematic.

1. Evolutionary species
concept
Hasnain Akmal

2. EVOLUTIONARY SPECIES CONCEPT
 According to this concept, species is “a spatio temporal lineage of populations that evolves separately
from other lineages and has its own ecological niche”.
 Not all taxonomists specially palaeontologists are not satisfied with the biological species concept.
 They preferred a definition of species which are related to the evolution.
 Simpson (1961) has proposed a definition with many modifications that is “an evolutionary species is a
lineage (an ancestral- descendant sequence of populations) evolving separately from others and with its
own unitary evolutionary role and tendencies”

3. EVOLUTIONARY SPECIES CONCEPT
 Simpson has stated that the above definition not only is consistent with biological or genetical
concept of species but it helps to clarify and to remove some limitations of the biological species
concept.
 Mayr (1982) has stated that the above definition is related to the phyletic lineage, not indicates a
species concept.
 The evolutionary concept is applicable only to the isolated population and incipient species but
not applicable to a single species.
 Simpson tried to solve the species definition by adding the time dimension in this species
definition.
 Reif (1984) and Mayr (1987) have stated that there are many demerits in evolutionary species
concept.

4. EVOLUTIONARY SPECIES CONCEPT
 Wiley (1978) has provided a revised definition of evolutionary species concept.
 He stated that “an evolutionary species is a single lineage of ancestral-descendant populations which
maintains its identity from other such lineages and which has its own evolutionary tendencies and
historical fate”.
 Mayr and Ashlock (1991) stated that the concept has developed on the basis of a species taxon, not of
the species category.
 Christoffersen (1995) proposed the ontological species concept that is “a species is a single lineage of
ancestral descendant sexual populations genetically integrated by historically contingent events of
interbreeding”.
 This definition of Christoffersen has given stress on the interbreeding nature of a species.