To begin, a definition of the key term being used. I will be using Douglas J. Futuyma's definition of evolution from
Evolutionary Biology (With quote taken from a site to be noted at a more relevant time later in this email). As follows:
"In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve. Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions."
I think that is said well, but to simplify it greatly: Evolution is change over time within whatever field is noted. The evolution of a galaxy is from the point it begins to the point it ends. The evolution of a social policy the same. Sometimes a thing evolves so much that it is impossible to reconcile with its previous form
(ie: capitalism and the communism which evolved from it a century ago). Evolution of a species occurs not dissimilarly, with individuals within changing over time and sometimes changing so much that no longer can we reconcile them as the same species. That is to say: the term 'species' is purely categorizational, as is galaxy, as is any social policy. Things occur whether we define them as one thing or another, and it is important to remember that a 'species', 'galaxy', 'bit of candy', or whatever else is only as it is defined.
Evolution only is change over time as defined here.
Also, there is no such creature as devolution, as change implies neither that it was good, bad, delicious, or ticklish. Only that it changed. There is no process by which anything can devolve save by never changing at all
I believe Laurence Moran's page on evolution
( http://www.talkorigins.org/faqs/evolutio...ition.html , the site I mentioned earlier) is quite adequate at explaining the definition of evolution which scientists use. It would do one well to remember that dictionaries are but lists of words, and neither sacrosanct or even scientifically or philosophically sound
(Try the 'faith', 'belief', 'trust' circular definition in most common dictionaries to see what I mean by how ridiculous they can be).
For the purpose of this discussion, any other definition used in argument is a straw man of the argument. I do not mind people knocking down or setting aflame the straw men they build up, so long as they understand that it in no way is an argument against the position held by the other side in a debate. If you accept evolution under the terms presented but deny definitions of it formed by less qualified/knowledgable individuals, you should likely find no argument here as most of those definitions are poorly formed.
And as I hope you at least accept that creatures belonging to a species differ from one another genetically
(if you don't, we are not arguing evolution but genetics itself), below is a somewhat well phased refutation of the perceived difference between small genetic changes within a species and changes over time that would have us define a new species.
http://atheism.about.com/od/evolutionexplained/a/micro_macro.htm
In short, there is no physical difference between the processes of diversification within a species and the formulation of new species: the difference here is purely categorizational
I also should hardly mind debating with any number of individuals using this definition of evolution. Evidence is less important in a debate than agreement upon the initial terms, as if there is a dissonance between these: that which is by one side of a debate conclusive evidence is utterly irrelevant to the opposition. That is why first we must agree upon either this definition, or a more accurate one that might arise out of it should there be some key feature missing from it (unlikely, in this case).
