Getting a little warm in this room...
Please forgive my intrusion into the biology forum, as I am a mere physicist. However, since this is the 'Physics Forums' site, what-the-heck ;-)
The first time I heard of a dichotomy between micro- and macro- evolution, it was in a biology setting, and not in any religious debate. To the best of my understanding and recollection, 'micro' referred to changes that do not alter the species of the target population, while 'macro' was used to describe cummulative changes resulting in speciization. Thus, as AUMath pointed out, the 'micro' cases are easier to accept, as they can be seen and experienced, while the 'macro' cases, generally, have not been seen or even reported in the literature. As examples, the large experimental data set of genetic mutations in fruit flies has been noted previously in this thread. However, to the best of my knowledge, in all the cummulative generations of fruit flies produced, no one has claimed to have observed or bred a new species of fly.
I am aware of several reports of speciization in recent history in the literature (primarily in plant species in isolated locations). However, I must note that, in order to report an observed occurence of a new species arising, the definition of 'species' was changed, compared to what it was in ancient times (back when I was in grad school).
As a physicist, I will use the terms 'micro' and 'macro' because they correlate to observable, reproducible effects with which I am familiar in thermodynamics and/or information theory. By way of simple analogy, I can shuffle two decks of cards and deal out 26 cards at random from each to produce a new 'deck'. I can repeat this process with stacks of new decks, and in only a few 'generations', I can produce decks that are all red, or all black, or made of all face cards. By isolating subsets of decks, I can produce whole populations of decks that are similarly skewed from the standard distribution in a new deck. I will not, however, no matter how many times I shuffle and deal, produce a deck that includes a three of potatoes, or a green ace. In other words, by adding energy, I can decrease the entropy of a specific subgroup of decks, but left to itself, this system will not yield new information. Even in genetic mutations in pathogens (also brought up earlier in this thread), those cases for which I am aware involve a net loss of genetic information.
Popular opposition to unequivocal acceptance of evolution arises from related experiences. Dogs, horses, and cattle are routinely bred to achieve advantageous features in subsequent generations. Subsequent generations, however, are still dogs, horses, or cattle.
So, in answer to the original post, are there reasons non-religious for opposition to macro evolution? Yes. Microevolution is observable, repeatable, can be modeled, and can be predicted, therefore it passes muster for having been 'proved' as much as any other scientific model (those who do theoretical work will understand my reluctance to use 'proved' in relation to scientific models). Macroevolution, on the other hand, has not been observed (unless the definition of 'species' is altered) or repeated. Therefore, I file it under "possible, but not confirmed".
Want to win me and thousands like me over to your 'side'? You have the tools - produce a new species of fruit fly.
