Hello D. K; There is certainly a variety of definitions for the species concept and most of them seem to be pretty taxon specific. At some point I assembled a little list of published definitions. Here is part of that list. Enjoy, Jim Des Lauriers

-----------------------------------------------------------

NORMAN; A species is what a competent botanist thinks it is.

A species is a group of individuals or populations with the same or similar morphological characteristics.

BURMA; A species, be it plant or animal, is a mental construction without objective existence.

HATCH; The species is one thing only, the concept that the taxonomist develops on the basis of his data.

GILMOUR; A species is a group of individuals which, in the sum total of their attributes, resemble each other to a degree usually accepted as specific, the exact degree being ultimately determined by the more or less arbitrary judgment of taxonomists.

SIMPSON; A species is the smallest persistent unit in nature.

A species is the largest group with non-arbitrary exclusion and the smallest group with non-arbitrary inclusion.

WILHELM; Species (of helminths) may be defined tentatively as a group of organisms the lipid-free antigen of which, when diluted to 1:4000 or more, yields a positive precipitation test within one hour with rabbit antiserum produced by injecting one 40 mg. of dry-wt., lipid-free antigenic material and withdrawn 10-12 days after the last of four intravenous injections administered every third day.

MAYR; Species are groups of naturally or potentially interbreeding natural populations which are reproductively isolated from other such populations.

THORPE; A population of individuals prevented from interbreeding with all other populations by physiological differences whether or not structural differences are present.

KINSEY; Species are populations having access to a common stock of genes.

LOTSE; A species is a group of genetically identical individuals.

DOBZHANSKY; species are formed at that stage of the evolutionary process at which the once actually or potentially interbreeding array of forms becomes segregated into two or more separate arrays which are physiologically incapable of interbreeding.

DU RIETZ; Species are the smallest natural population permanently separated from each other by a distinct discontinuity in the series of biotypes.

In my opinion, taxonomists defined the species as a group of individuals which, in the sum total of their attributes, resemble each other to a degree usually accepted as specific; based on some acceptable criteria that are characteristic to each group of individuals. However, there's a gap, that should be filled, resulted from the isolation between biologists and paleontologists.

While we seem to be stuck with the Linnean taxonomic system of naming, I think the phylogenetic species concept combined with morphology and ecology makes the most sense when defining taxa. What is called a "species" can be clear and obvious, but it often is not and intermediate lineages should always be recognized as unique products of evolution whenever we have the knowledge to do so.

Hello all; The tension between phylogenetic species concepts and morphologically based ones is in the field utility of whatever definition is currently in use. In the field it is critical that the researcher knows who is being observed. That spoken by a field observer! In the western USA, the ant genera Lasius and Crematogaster, for instance, are replete with sympatric lineages whose characters overlap broadly. Some of them are probably good species but you sure can't tell by looking. So, there seems to be a need for a utilitarian use in the adopted definition. That's the tension! Best regards, Jim Des Lauriers

Dr. @D. K. Agarwala,

I think being Editor of Publications, the answer is best known to you.

In my opinion.species is a group of individuals population getting in own characters change geographical condition (evolutionary) factor so that celled species that process speciation.