Evolution Explained (Well, kinda, you'll see...)
Now, while the actual scientific community (Behe, Dembski, and Gish ≠ scientists) makes no distinction between Micro and Macro-Evolution (given that they are the same thing with the only differentiating factor being length of time), I shall momentarily use the aforementioned terms in an effort to break something down for the genetically less fortunate among us.
Micro-evolution is undisputed. Seemingly because this is completely obvious given the clear changes we see in species and the thrusts in biology that have come about as a result of the said changes and predictions that followed. However, the religious right has launched a war on the idea of some species coming about from others due to evolutionary processes. While it is clear that their arguments hold no water scientifically, it is not commonly pointed out that in accepting micro-evolution they have in effect accepted macro-evolution and are contradicting themselves.
Over long periods of time through the process of evolution we are able to see changes on small scales that opponents of the generally accepted notion of evolution refer to as Micro-Evolution. These small periods, say perhaps 50 to 100 generations, that we map out in the species we are studying provide ample evidence of this, so for them to argue this point would be futile and hence they do not.
Macro-Evolution is said to be impossible because on their account species CANNOT evolve into other species. However, here is the scale through which it would occur:
Original Species: G
Different appearances due to "micro-evolution" GH GI
New change in species over several generations HJ IK
(Notice: What made original species distinct=gone) / \
Same species continues to change JL KM
(Notice how far removed now) / \
Over many generations new species forms LN MO
The final formations now share common characteristics with the last step from which they emerged yet they can no longer breed with it or perhaps the earlier forms from which it evolved due to a mass amount of evolutionary changes over time.
Perhaps this is a bit too watered down but it's something that may help explain this process nonetheless.