I am sorry but I never said the term "species" is arbitrary. It most certainly is not. It can be called artificial because it is something invented by mankind. However being an artificial construct does not make it arbitrary or less applicable to the natural world. It is a descriptor applied to natural phenomenon and is clearly defined in that respect. The fact that there are some instances that render its application difficult does not invalidate the term. For the term to be applicable in all cases is what required the introduction of the notion of a "species complex".
Sorry, Blue. I completely agree that "species" is artificial, but that does not mean that the term has no applicability. Obviously my utilization of the term "arbitrary" has caused some confusion between us. And I think I know where this has come from. I believe that we are looking at evolution from two different angles, though not completely so (hopefully that will make sense in a minute). I believe that you are looking at this more from the point of view of a modern-day observer, looking at the differences, both phenotypic and cryptic (as molecular studies are now elucidating), in contemporary species. You are looking at this from a taxonomic point of view, whereas I am looking at this from a different angle:
When I say that the term "species" is arbitrary, what I am referring to is that over geological time the changes within a species, which accumulate (eventually producing large-scale differences if the species persists for long enough) may produce a new species. But this process occurs so slowly that it is arbitrary to make distinction as to when one species has become another. Let me take a simple case of phyletic extinction (that is, one species becomes extinct because it evolves into another, for those who don't know), whereby species "A" evolves into species "B". Since all evolutionary change is gradual, there is no better place to make the "divide" between species "A" and species "B" than any other place. Any point at which we make the divide is rather arbitrary. That is what I mean, Blue.
I agree that in both taxonomic and conservation contexts (though you never mentioned the latter), the term is vital. To start with the latter, on several occasions that I'm aware of, what was once considered to have been a single geographically wide-ranging species has turned out to be a species-complex of several genetically distinct species. This can have immediate conservation implications if these newly described species only have relatively small geographic distributions. And again, in the context of taxonomy, the idea of species certainly isn't superfluous. But I think that you will find that there is an overlap between when various taxonomists classify a population as a subspecies of a species, or as a species in its own right. The fact that the term "species" has utility in a taxonomic context does not help your case in arguing that the production of new species is the defining feature of biological evolution, if you were so inclined to that view.
The original biological definition of species has not always been amenable to the practical application required in museums and similar institutions, where identification of specific species takes place. However, use of genetic data is now helping to overcome that shortfall. If there is inter-breeding between individuals of populations, this shows up in the genetic profiles. Hence decisions can be made on whether populations are interbreeding or not in nature. There is nothing arbitrary about this. It is a clear and concise requirement of the definition of a species that the individuals do not breed with other populations under natural conditions.
Unfortunately it is not quite as simple as that, Blue. There are many hybrid-zones between different species belonging to the same genus. The biological species concept (BSC), like all others proposed, does not have sufficient generality to be applicable under
all circumstances.
I think the difference in our viewpoints may come about due to the common language meaning of evolution as something which undergoes change. I have only been referring to the biological definition, which relates exclusively to how new species arise or how existing species arose. It most certainly is a process of change – slow, accumulated change. What makes it different from the common term is what it applies to – the development of new species. If you remove that single aspect, then you are no longer dealing with biological evolution.
I am meaning evolution in a purely biological sense too, Blue. I find the term to be wholly invalid when applied to other areas such as the "evolution" of the universe. What you seem to be saying is that the production of new species is what separates biological evolution from other types of "evolution". But my own definition of evolution fills exactly the same need! Only living organisms (or deceased ones) have alleles. So your grounds for arguing that the production of new species is the defining element of biological evolution are untenable. There are plenty of other differences between biological and any other process which has been given the (misleading) name "evolution".
I must say that it sounds like we agree on the use of the terms microevolution and macroevolution. I have never used these terms. I believe that all they do is compound and confuse that which should be relatively straight forward.
The two terms certainly do confuse many people. By using two different terms people get it into their heads that micro- and macroevolution are fundamentally different, which they most certainly aren't.
I suspect we are more on the same page than our academic discussion would indicate.
I agree, Blue. The only difference between our views seems to be what the defining feature of evolution is, which really is quite a small difference on the scale of differences. But hopefully what I have written above will give you a better idea of where I am coming from compared with my previous posts. Perhaps I still do not fully understand where you yourself are coming from, but no doubt you will set me straight if I have it wrong. And so the discussion can move forward.
