Recently, I heard species defined in an elementary science text book that simply defined “species” as living organisms that can mate. Then, this section of text gave an example (both in words and by illustration) of how biologists use their classification system to whittle down a cross section of animal life, for example, to one specific animal. (For example: From jellyfish, dog, and crab down to dog).
This got me thinking, though. I always thought those fancy Latin names giving us genus and species were very specific, but it seems it is not. So, based on the present system, how can one tell a Poodle from a Great Dane? Does the classification system delve into sub-species? And, what about a Black Lab from a Yellow Lab? Shouldn’t there be a system that gets into the nitty gritty? - Jinx
All dogs are the same species, if that’s what you’re asking, and can theoretically mate with one another. Although size becomes a complicating factor at the extreme ends of the spectrum. In Labradors, the difference between black, yellow and brown is controlled by just a pair of genes – Labs of one color can (and often do) give birth to Labs of other colors. In dogs, there is little scientific or genetic reason for categorizing breeds – the parameters are set by arbitrary aesthetic judgments from the imbeciles who populate kennel clubs.
Of course, the complicating factor is that the concept of species is fluid and poorly defined. The old thinking was that a species is a group of animals which can mate and produce fertile offspring. That excludes infertile hybrids like mules, but there are also lots of fertile hybrids like various cow/bison breeds that have been developed by ranchers. (My favorite is called the Beefalo.) So are they cows, buffaloes, or a new species? The fact that they can all mate with each other makes that question hard to answer.
In Linnaean taxonomy, there is a concept of subspecies, and some species have them categorized. They are usually used to describe geographically distinct populations of species which would otherwise be classified as the same. For example, the Wikipedia article cites the example of the Dingo – officially categorized as Canis lupus dingo despite being perfectly compatible with domesticated dogs, C. lupus familiaris, and the wolf, C. lupus.
It is a method of further refining the classication system, if that level of distinction is desired. For example, it is very common in landscaping to see a finer distinction than species - in most instances, it is referred to as “variety”.
So, Acer palmatum refers to a Japanese Maple, and is usually considered to be the one with green leaves. Acer palmatum ‘atropurpureum’ makes the further distinction that it has light red or purple leaves. And Acer palmatum ‘atropurpureum’ Oshio Beni takes that one step further to refer to a very specific variety of tree. A walk around any nursery will show specific varieties listed after the species.
[QUOTE=Jinx]
Recently, I heard species defined in an elementary science text book that simply defined “species” as living organisms that can mate.
[quote]
It’s a little more complicated than that. The BSP (Biological Species Concept) defines a species as any population that regularly interbreeds in the wild. Lions and Tigers can interbreed, but they don’t do so in the wild. Wolves and Coyotes can interbreed, and they sometimes do in the wild, but not “regularly”. (That last bit is always going to be a bit subjective.)
I don’t know what you mean by “whittle down”. Can you clarify?
Anything above or below the level of species can be controversial, although there tends to be general agreement on Genus.
The problem arises do to historical inaccuracies. Originally, taxonomic classification was done by comparing animals’ morphologies. This works pretty well, but it can sometimes be misleading. You may look at 3 populations (A, B and C) and conclude that A and B are more closely related than either is to C, and so you put And and B in one Genus and C in another. But if you preform DNA analysis, you may find that B and C are actually more closely related (ie, the have a more recent common ancestor). That generally causes biologists to either group A, B and C into the same Genus, or to split the Genera differently.
As for subspecies, that doesn’t really mean too much other than that you have found two populations that would normally be one population, but are separated by some barrier and so don’t interbreed much except in a narrow overlap zone.
You can think of a subspecies as a “species in the making”, if the barrier between the two groups becomes permanent and there is no gene flow between the two populations.
With domestic animals, the BSC is problematic since it requires that the populations exist “in the wild”. By definition, biologists generally just put domestic animals in the same species as their closest relatives in the wild (sometimes designating them as a subspecies, but sometimes not). A breed of dogs is not the same a subspecies because the populations are artificially controlled by humans. Although there are genetic tests that can tell the difference between some breeds of dogs, generally you need to look the whatever Canine Association is in charge of defining the breed standards.
It’s a little more complicated than that. The BSP (Biological Species Concept) defines a species as any population that regularly interbreeds in the wild. Lions and Tigers can interbreed, but they don’t do so in the wild. Wolves and Coyotes can interbreed, and they sometimes do in the wild, but not “regularly”. (That last bit is always going to be a bit subjective.)
I don’t know what you mean by “whittle down”. Can you clarify?
Anything above or below the level of species can be controversial, although there tends to be general agreement on Genus.
The problem arises do to historical inaccuracies. Originally, taxonomic classification was done by comparing animals’ morphologies. This works pretty well, but it can sometimes be misleading. You may look at 3 populations (A, B and C) and conclude that A and B are more closely related than either is to C, and so you put And and B in one Genus and C in another. But if you preform DNA analysis, you may find that B and C are actually more closely related (ie, the have a more recent common ancestor). That generally causes biologists to either group A, B and C into the same Genus, or to split the Genera differently.
As for subspecies, that doesn’t really mean too much other than that you have found two populations that would normally be one population, but are separated by some barrier and so don’t interbreed much except in a narrow overlap zone.
You can think of a subspecies as a “species in the making”, if the barrier between the two groups becomes permanent and there is no gene flow between the two populations.
With domestic animals, the BSC is problematic since it requires that the populations exist “in the wild”. By definition, biologists generally just put domestic animals in the same species as their closest relatives in the wild (sometimes designating them as a subspecies, but sometimes not). A breed of dogs is not the same a subspecies because the populations are artificially controlled by humans. Although there are genetic tests that can tell the difference between some breeds of dogs, generally you need to look the whatever Canine Association is in charge of defining the breed standards.
There are what are known as infrasubspecific taxa (classification categories) which are ranked collectively below that of subspecies. These are all considered unofficial, in the sense that the International Code for Zoological Nomenclature (ICZN) and the plant equivalent, the International Code for Botanical Nomenclature (ICBN) does not make any particular rules about their use / disuse. These infrasubspeciifc categories include race, morph, variety, form, phase, etc. Categories within this group are not themselves ranked (that is, nested within a hierarchy, as are higher rankings such as Class, Order, Genus, etc.).
Oftentimes, taxa such as morph, phase or form might be used to describe individuals or subpopulations composed of individuals which exhibit particular morphological differences at various times in their lifecycles (e.g., caterpillars vs the adult forms for butterflies or moths).
As far as domesticated animal species go, we often use the concept of “breed”, which is, in essence, another infrasubspecific category. It’s a further refinement of a species based on particular traits of a populaton, but one that holds no “official” status as far as zoological nomenclature is concerned (though in the case of breeds, at least, there are regulatory agencies which serve to define them; such agencies are independent of the ICZN & ICBN, however; the AKC for example. There may be various horticultural organizations which do the same for, say, roses, as well).