The definition of species is still under debate within scientific circles. This is what Tim Gamble, Chris Durden, and Ron Gatrelle have written.
I hope this helps.
Here is a quick review:
The morphological species definition:
A species has several features that are not shared by other groups.This is the oldest definition which is solely based on "visible"features. The main problem with this definition is the question howdifferent to groups have to be before they can be considered asseparate species. Also creating problems is the fact that there oftencan be considerable differences in appearance among members of thesame species, just look at the variation among Homo sapiens.
The biological species concept:
A species is a group of interbreeding individuals that arereproductively isolated (in place, time or behavior) from othergroups. All members of the group share a common ancestor. The speciesis the fundamental unit of evolution, while higher taxa (families,orders, etc.) are artificial groups reflecting a possible evolutionaryrelationship. Thus, species that may interbreed in the unusualcircumstances of captivity (such as the large cats) do not qualify asbelonging to the same species since they normally would not interbreedin the wild.
The Genotypic Cluster definition:
A species is a common genetic pool that are identified by theirgenetic differences from other groups. This is the latest, andprobably most accurate, definition which is based on differences inDNA sequences. The problem is that this is also the least practicaldefinition. Gene sequencing is complicated, costly and time consuming.It cannot be done in the field, where biologists must still relay onmorphological characteristics for quick identifications.
-- Tim GambleCharlotte, NC
Mayr’s biological species concept – ‘groups of actually (or potentially)interbreeding natural populations which are reproductively isolated fromother such groups’. (defining species in relation to other species)
Paterson’s recognition concept of species - ‘that most inclusive populationof individual biparental organisms which share a common fertilization system’. (defining species as having a specific-mate recognition system; and notin relation to other species)
These definitions can only relate to sexual species, and also are notimmediately helpful to taxonomists.
Taxonomy only DESCRIBES species, and does not attempt to DEFINE species.
Species concepts like Patterson’s and Mayr’s, are attempts to DEFINE species(in nature).
So I guess it is difficult to say what a DEFINITION of species is intaxonomic terms.
Should we try to group together taxa based purely on morphology, or shouldwe try to incorporate as much biological data into revisions andclassifications?
Could separating a species from a genus be a valid decision if based purelyon biological differences (if the difference is radical).(I dont have a specific example, but am curious if anyone knows of such acase, or can comment in general)
Is species biology an unrealiable character for taxonomy, because the'whole' biology cannot be observed.And, if incorporating biological data into taxonomic work, what should onebe wary of?
I am really just starting out as a taxonomist and am asking these questions.Does anyone have any advise for a beginner who wants to get started on theright path.
This a meaningful point of view.
Anyway, the problem of the relationship between 'theorical species'(definition) and 'taxonomical species' (identification) comes only afteranother bad problem: the biological concept of species does not easily applyto all organisms (think to not-sexuate organisms, or to species generated bythe hybridisation of other species - more common in plants than in animals).
So it seems almost impossible giving a single DEFINITION of species fittingfor all organisms.
Coming back to the identification of species, it is obviously impossible togroup , as a rule, populations in species by studying their capability ofinterfecundate...the most easy way to study the single specimens orpopulations is the morphological or molecular approach.Let's remember that, nowadays, the classification of organisms should bebased on phylogenetic trees.Consequently, wheter a single species belong to a genus or to another is notdepending from its characters (morphological or biological), but from itsposition among its relatives.Of course, this can lead to strange situations... for example, now we knowthat birds are not a class, or at least, they are not at the same rank ofthe class Reptiles. They are just a group emerged from the Reptiles... verydifferent from all other reptiles, but included in the radiation of them andhaving the same rank of crocodiles and turtles.So, we have not to look at the single taxon, but at his position in thephylogeny of his group.Obviously, when phylogenetic data are absent, or poor, we are forced to takeprovisionary decisions based on morphological or biological traits.
Hope this help, and hope my english is clear enough.
All higher categories (family, genus, etc.) are artificial and man-made and you may never get a finite definition. Obviously, even Orders (e.g., Orthopteroidea) have had drastic shifts in definition recently.
On the other hand, "specie" is defined in the dictionary as "Minted money; coin", although in Latin it means "kind". The word you really wanted is "species" which is the same in singular or plural. Although various definitions have been proposed (especially in biology), they usually include " a category below genus, which consists of organisms capable of interbreeding". Although there are many definitions, and hundreds of papers have been written on "what is a species", the main belief is that they exist in nature (in possible contrast to the man-made higher categories). The only problem (and that is a taxonomist's job, and why we write "revisions") is how to distinguish them from each other! Bob Woodruff, Emeritus Taxonomist, Florida State Collection of Arthropods.
For those who are interested in such topics I can recommend two excellent papers:
Mayden R. L. 1997. A hierarchy of species concepts: the denouement in the saga of the species problem. In: Species: the units of biodiversity: [pp 381–424.] (M. F. Claridge, H. A. Dawah and M. R. Wilson, Eds.). Chapman & Hall, Melbourne.
Ereshefsky, M. 1998. Species Pluralism and Ant-Realism. Philosophy of Science 65: 103–120.
There are references to many other studies that discuss the species concept in many different ways and contexts. If anyone is interested in the Mayden paper, I have it here as a PDF. Email me privately (not via the list) and I can send you a copy.
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Last modified on Sunday, 3 January 2016