897tgigvib
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It is true that the word species has several definitions.
In the world of plants and people it is very common that we use the word species incorrectly. Well, we do, at least incorrect as far as compared to the strictest biological definition.
Some of the well validated and used definitions of species are:
1) Common use.
With common use being the definition of species, there are many dozens of species of Roses, and I guess every one of them will very freely cross with every other one. The wildest Siberian Rose will freely cross with the fanciest award winning Hybrid Tea Rose, yet they are called different species of Rose. Not only will these examples readily cross, but their descendents will readily and freely cross with either of their parent species of Rose or with any other species or crossed up hybrid.
This common use is traditional. But really, those separate species of Rose are more like subspecies of one more encompassing species.
Here is why:
2) Biological definition of species. This definition of species is cut and dry, easy to understand. "If they can breed and produce viable offspring which can contribute to either parent's gene pool, then they are the same biological species."
With the Biological definition of species, all Roses are the same species. (Ok. Someone will find an exception.) To test how well this was understood, test question: Are horses and Donkeys the same Biological species?
No. The offspring mules can't contribute to either parent's gene pool because mules are all sterile, wild assertions of not sterile mules aside since none has ever been truly proven.
3) Phylogenetic definition of species. This one is actually only a bit trickier, all 15 syllable words notwithstanding. (Scientists adore long words. To keep them happy, we let them invent them. Makes them feel good.)
With this definition, the scientists decide how long it has been since there was a common ancestor between 2 or more groups in question. (Huh? That's what I said in 1996). They look at things that stopped this Squash from crossing with this other Squash. Oh boy! The isthmus of Panama closed 5 million years ago.
This is the definition Evolutionary Biologists are using these days. Reference Gerald I. Davis at Cornell, 1997, Bioscience Journal. They use this definition to make those graphic evolution lines you sometimes see in National Geographic. Darwin was the first to publish one, but he got the idea from his friend Huxley's version of one after he mentioned it to him that his grandfather Erasmus was sketching them. There are nowadays all kinds of rules for them to follow.
We can kind of never mind this definition, but should know that our scientists use it to help the Genetic Definition get better.
4) The Genetic Definition of species uses the modern tools of DNA sequences to define species. That may be extremely precise, and certainly seems to be. A big huge however is needed here though.
The Genetic definition of species absolutely needs to correspond with one or more of the other definitions of species for some sort of a benchmark. Until this definition of species can find what it is that makes one Squash not be able to cross with another Squash it is of no use to the plant breeder. Or, more realistically, some new found Lily from the jungle of Borneo compared with another Lily from Malaysia.
I am like most people and follow the common definition of species, but with my tongue in my cheek, just to avoid conflicting views. But, deep inside, I adhere to the Biological definition of species. That means I'll agree there are many species of Roses, but I know there really is only one unless there are a few rare exceptions out there.
I needed to clear that up before continuing with varieties.
In the world of plants and people it is very common that we use the word species incorrectly. Well, we do, at least incorrect as far as compared to the strictest biological definition.
Some of the well validated and used definitions of species are:
1) Common use.
With common use being the definition of species, there are many dozens of species of Roses, and I guess every one of them will very freely cross with every other one. The wildest Siberian Rose will freely cross with the fanciest award winning Hybrid Tea Rose, yet they are called different species of Rose. Not only will these examples readily cross, but their descendents will readily and freely cross with either of their parent species of Rose or with any other species or crossed up hybrid.
This common use is traditional. But really, those separate species of Rose are more like subspecies of one more encompassing species.
Here is why:
2) Biological definition of species. This definition of species is cut and dry, easy to understand. "If they can breed and produce viable offspring which can contribute to either parent's gene pool, then they are the same biological species."
With the Biological definition of species, all Roses are the same species. (Ok. Someone will find an exception.) To test how well this was understood, test question: Are horses and Donkeys the same Biological species?
No. The offspring mules can't contribute to either parent's gene pool because mules are all sterile, wild assertions of not sterile mules aside since none has ever been truly proven.
3) Phylogenetic definition of species. This one is actually only a bit trickier, all 15 syllable words notwithstanding. (Scientists adore long words. To keep them happy, we let them invent them. Makes them feel good.)
With this definition, the scientists decide how long it has been since there was a common ancestor between 2 or more groups in question. (Huh? That's what I said in 1996). They look at things that stopped this Squash from crossing with this other Squash. Oh boy! The isthmus of Panama closed 5 million years ago.
This is the definition Evolutionary Biologists are using these days. Reference Gerald I. Davis at Cornell, 1997, Bioscience Journal. They use this definition to make those graphic evolution lines you sometimes see in National Geographic. Darwin was the first to publish one, but he got the idea from his friend Huxley's version of one after he mentioned it to him that his grandfather Erasmus was sketching them. There are nowadays all kinds of rules for them to follow.
We can kind of never mind this definition, but should know that our scientists use it to help the Genetic Definition get better.
4) The Genetic Definition of species uses the modern tools of DNA sequences to define species. That may be extremely precise, and certainly seems to be. A big huge however is needed here though.
The Genetic definition of species absolutely needs to correspond with one or more of the other definitions of species for some sort of a benchmark. Until this definition of species can find what it is that makes one Squash not be able to cross with another Squash it is of no use to the plant breeder. Or, more realistically, some new found Lily from the jungle of Borneo compared with another Lily from Malaysia.
I am like most people and follow the common definition of species, but with my tongue in my cheek, just to avoid conflicting views. But, deep inside, I adhere to the Biological definition of species. That means I'll agree there are many species of Roses, but I know there really is only one unless there are a few rare exceptions out there.
I needed to clear that up before continuing with varieties.
