Then you have not been paying attention, since I've posted the same or similar comments here innumerable times.
Thanks for finally noticing.
annalex: "So is the definition of species "specimens that do not naturally interbreed" or is it "specimens that cannot produce a viable offspring regardless of conditions"?
Of course, you can look that definition up yourself -- simply type in the words "definition of species" in your address line, and up will pop any number of sites with dictionary and encyclopedia type definitions.
Here is a typical definition from Wikipedia:
So my interpretation would be more along the lines of: "sub-species which do not naturally produce viable offspring have become separate species."
For example, horses and donkeys are separate species because their forced off-spring -- mules -- are not viable in nature.
Various sub-species of Zebras -- for examples, Burchell's and Celus Zebras -- are not speparate species because they can and do interbreed in nature.
By contrast, Gevy's Zebra does not naturally interbreed with those others, and when forced (i.e., in a zoo) more often produces offspring which are not viable in nature.
This is clearly evolution "caught in the act" of species differentiation.
Please understand, the ability (or lack of ability) of sub-species to interbreed is not the only factor defining separate species.
That's because this ability (or lack of) normally corresponds to several other factors which confirm the designation of sub-species or species.
Those other factors include DNA analyses showing percentages of differences between one group's genome and another's.
So, the higher the percentage of difference, the less likely are those groups to naturally interbreed, and scientists will therefore consider them separate species.
Where exactly is the DNA dividing line between sub-species and species?
Individual species have different results, and it probably matters just where exactly these DNA mutations show up, but for, say, humans that number is less than 1%, putting for example Neanderthals right on the ragged edge between sub-species and species.
annalex: "Bonus question: Are dogs (insert a picture of a daschund and a dane here) a group of species or a single species?"
The separation of dogs from their wolf ancestors was even more recent than the separation of humans from our pre-human ancestors, and so the generation-by-generation buildup of DNA mutations has not been nearly enough to make dogs a separate species from wolves, much less from each other.
Dogs and wolves still interbreed, so by scientific definition, they are still the same species.
annalex: ""therefore, while mutations do occur in subspecies differentiation, they are not the mechanism or at least not an essential mechanism. "
True, but only up to a point.
Consider, for example, the various differences between African elephants and woolly mammouths.
Some of those differences humans could engineer simply by breeding elephants and selecting for cold weather adaptations -- i.e., longer hair, smaller ears.
But other differences could not happen until DNA mutations came along to cause them.
Precisely which changes came from natural selection and which from DNA mutations is a matter for scientific analyses to show.
And the key point to remember is: as DNA mutations build up over many generations, allowing for more and more radical adaptations among separated sub-species, so also does the difficulty of these separated sub-species to interbreed with each other.
In short: the more specialized their adaptations, the more likely they will be unable to interbreed, and thus scientists will classify them as separate species.
annalex: "It is another picture of zebras, to show you that I can post pictures too."
Great work!
The abilities to quickly post photos, links, emphasis, extreme emphasis, bullet points, block quotes and yes, font colors, are all learned skills -- no DNA mutations required ;-) -- skills which improve with practice.
They can add interest and clarity to any post.
I will get to this later. Thank you.
You did. My comment was referring to the post I was responding to, in which I only found that aspect in need of a reply.
my interpretation would be more along the lines of: "sub-species which do not naturally produce viable offspring have become separate species."
OK. Then there is no argument: according to this definition that third kind of zebra is a new species. But the definition is flawed: if you define species by their behavior in mating, then dogs are also not a single species, because big dogs and small dogs do not naturally interbreed: the hydraulics and the mechanics don't work. Also - as I noted before more than once, -- humans, too, have breeding preferences which they do not cross other than in "captivity" of some kind, i.e. are forced to or exchange reproductive products through things like sperm banks.
The definition of species, in my mind, needs to include other factors: can the specimens be bred in a lab? do they look alike? does the offspring itself reproduce? These are all factors generally recognized as a part of a definition: Species problem.
According to the latter, all these zebras are breeds of the species zebra.
Note, too, that this quadrille about definitions does not help the evolutionist myth. Sure one can define species so that they "evolve" all the time. But then you discover that maybe they do "evolve" according to your particular definition, but that "evolution" still confines the "evolved" specimens to a boundary that is not crossed. Evolution postulates that bona fide species evolve into species different in many ways. Further, the evolutionary hypotheses speculates that genera boundaries are crossed as well (e.g fins become legs, front legs become wings, etc.). So your zebra example falls still short: you simply adapted your definition of species to be narrow enough for it to show "speciation".
Dogs and wolves still interbreed, so by scientific definition, they are still the same species.
They interbreed under special conditions: in a lab, involving feral dogs, in captivity, etc. They do not naturally interbreed when mates of their own kin are available. I agree they are the same species, but so are the three zebras.
But other differences could not happen until DNA mutations came along to cause them.
But they are mutations inside the genome of an elephant or of a dog. They may help in artificial selection, but they do not work across species or at least across related fuzzy group you insist on calling separate species.
This would, indeed be a good avenue of research to pursue for someone interested in proving macro evolution. Start with a dog, and make a cat. Or the other way around. Or anything that is a non-dog and itself can breed. That would prove that random mutations with selection produce something selection alone could not produce.
That would also be what the scientific method calls for: test your theory with experimentation.