It can sometimes be quite confusing to tell the difference between the two. Most people know what a species is, but the definition for subspecies gets a bit hazy and subjective and the difference gets blurred in the process.
Technically, a species is a population or groups of populations that can potentially interbreed freely within and among themselves. This is a naturally-defined concept, something which exists by itself, whereas a subspecies is a subgroup with different traits, as defined by scientists. Let’s look at it in depth.
What a species is
In 1735, Carl von Linné revolutionized biology by introducing a new system of classification – a modern taxonomy. The species is the basic unit of this taxonomy. Species are grouped in a genus, genera are grouped into families, then orders, and so on for all living beings.
Biology is based on that taxonomy, which is why you see plants and animals having scientific names – this is the system that Linné created. Now, something as important as a species has to be clearly defined and it is, to a point. Different species are simply different animals, distinct kinds of organisms. They can’t breed with each other. Even if they do create offspring, the offspring will be sterile. Think of donkeys and horses for example – they can have offspring (mules), but they will be sterile.
Now, this inability to breed is what most biologists focus on but there are a number of concepts which refer to species. Thanks to differences among different groups of organisms and arguments among systematists as to the best definition, there is no definition to fit all these concepts. There are also some defining characteristics for a given species, but genetic studies are often expensive and difficult to conduct.
It gets even more complicated when you factor in evolution. Linné published his systematics a hundred years before Darwin wrote his theory of evolution. Evolution is a continuous process, and geographic variations are inevitable. This means that the same species living in two different areas will start to have different traits. If they’re isolated for a long enough time, they can become different species, but the exact moment at which this happens is very hard to pinpoint.
Furthermore, it can be extremely difficult to apply the same reasoning across all of biological life, from bacteria to complex mammals, which is why the concept of a subspecies was introduced.
What a subspecies is
A widely accepted definition is that of Mayr and Ashlock (1991:43): “A subspecies is an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision of the range of that species and differing taxonomically from other populations of that species.”
As you can imagine, a subspecies is subordinate to a species. That means that while you can have a species of its own, in a genus of its own, you can’t have a subspecies of its own. You need to have a subspecies of a species, and in order for the idea to make sense, you need to have two different subspecies. This is where things start to get even murkier.
It all started with population variation. Biologists studying mammals saw that across the same species, individuals could be very different. You could have for example a mammal of a different color, or with a different behavior, but they were still the same species. Virtually every population differs to some degree from every other population of a species, but that doesn’t make them a subspecies. If that were the case, then you’d have a whole lot of subspecies and any utility for a taxonomic classification would be lost. But at one point, the differences between some populations become so significant that they simply can’t be considered similar. But it’s the genetic differences which are most important here.
Take dogs, for example. Different dog breeds can be very different from one to each other (think about a chihuahua and a German shepherd), but they’re not even considered different subspecies. The main reason for this is that dogs originated from domesticated wolves, and there is less genetic variation between dog breeds than between wolves – even if they look so different. So without a genetic analysis, it’s really hard to define a new subspecies and even with it, things aren’t so clear.
So, what’s the difference?
Basically, the species is the largest group within which interbreeding produces viable offspring. The subspecies is loosely defined and the name should be used with much caution because it requires much familiarity with the particular species, and the philosophy through which it got its subspecies status. It’s not necessarily an intrinsic concept whereas the species is. The breed is not the same thing as the subspecies, it usually refers to a domestic population with little genetic variation.
Even though it’s a vital concept, biologists sometimes differ on the details of both the definition of species and the mechanisms of speciation, the mechanism through which a new species is created through evolution. So it can be extremely difficult to say when a new subspecies starts to emerge or when a subspecies becomes a species in itself.
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