What is a species: Conflict between evolutionarycontinuity and taxonomic discontinuity
2016
What is a species? This is a question seemingly simple but difficult
to be addressed clearly. If only by a simple definition, a “species”
can be described as the basic category or unit for taxonomic classification
of organisms (including animals, plants, and microbes). On the other
hand, it is extremely difficult to define a “species”
or “species concept” that are generally acceptable by
all biologists. Substantial debates exist over the “species
concept” and have lasted for more than a contrary. During this
time span, many species concepts have been proposed by various groups
of biologists who work in different disciplines. However, it is extremely
difficult to have a clear definition for “species” and
particularly for “species concept” that are universally
agreeable. Among the proposed species concepts, only some of them
are influential, including those: taxonomic species concept, Darwin’s
species concept, biological species concept, genetic species concept,
and phylogenetic species concept. Obviously, biologists who proposed
their species concepts attempt to interpret what “species”
are only by emphasizing the specific features of a species appreciable
from their perspectives. For example, biologists who have proposed
taxonomic species concept highlight the classification feature of
a species; whereas those who have Darwin’s species concept
stress the evolutionary process of a species. Disagreements always
exist among biologists when define the species concept. Some biologists
believe that a species is a natural unit, which is strictly followed
for the classification of a species. However, other biologists do
not believe a species to be a natural unit, instead, they emphasize
more on the evolution and reproductive aspects of a species. The extreme
groups even reject “species” as a natural units. They
only accept individuals as the natural unit. Obviously, the dilemma
is due to the diverged understanding and opinion of species. We know
that species are the outcomes of evolution—biodiversity. From
the practical viewpoint, it is necessary to categorize the evolution-resulted
biodiversity using a stable classification system. Therefore, taxonomists
prefer to use a discontinued unit to classify species. On the other
hand, evolutionists emphasize more on the variation of organisms.
Thus, the characteristics of evolutionary continuity and taxonomic
discontinuity have stimulated such debates over a species—a
natural unit or an artificial category. Species are outcomes of continued
evolutionary process and categories of discontinued taxonomy. As such,
one can recognize, understand, and define a species according to the
objectives and demands to suit his or her research, without being
troubled too much by a universally unified concept of species. Thus,
to answer what is a species, we prefer the definition that a species
is an individual collection that occurs in a particularly space/time,
shares similar morphological and physiological features with a common
ancestor. Members of the same species are able to interbreed and reproduce
normal descendants.
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