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Macroevolution, in the world of science, is the result of microevolution which takes place between two groups within a species. Although distinct from microevolution, the two concepts are inextricably linked, and it is impossible to have the concept of one without the other in a complete theoretical framework.
 Macroevolution vs. microevolution
Macroevolution is what results when microevolution occurs in two or more populations within a species. Or the net sum of all the microevolution that occurs within a species. Either way, it's impossible for microevolution not to imply the possibility of macroevolution.
Suppose there was a large population of Species A (let's just suppose, for fun, that they're salamanders) that lives in a hilly terrain. Everything's fine and dandy until some event (like an ice age) comes along and isolates different groups on the mountaintops. Hopefully, that makes sense so far.
It shouldn't be much of a jump to assume that those different populations, no matter how similar, still have slightly different mutations and develop under slightly different conditions. Given enough time (or enough of a difference in conditions) these two groups will develop into very different populations, and when they come back together, they may not be able to inter-breed. Et voila! New species.
So there we have it: "microevolution" is what happened to each individual group. "Macroevolution" is the result when the two groups develop under different conditions. And it may sound like an esoteric example, but guess what?! It's actually happened!!!! The "theoretical" situation accounts for the diversity of salamanders in Appalachia.
Is it possible to have microevolution without macroevolution occurring? Sure...if there's no reproductive isolation, the species will keep micro-evolving quite merrily, no matter how long it has. But as soon as something isolates two or more groups, it sows the seeds for new species via macroevolution. And is it possible to have macro without the micro? Absolutely, and there are documented cases!
 Macroevolution without microevolution
Although the vast majority of speciation occurs via microevolution resulting in macroevolution, it is possible to skip the micro and create new species out of the blue. Although seemingly outlandish and admittedly rare, this has happened before.
In North America, there are two species of gray tree frog. For all intents and purposes they are identical, and they differ in only two features: their call (necessary to isolate the groups) and their genetic make-up; the species simply referred to as the Gray Tree Frog (Hyla versicolor), pictured in the top right image, has four copies of each chromosome, whereas the Cope's Gray Tree Frog (Hyla chrysoscelis), pictured in the bottom right image, has two (like humans). At some point in their history, a single group of larvae was born with four sets of chromosomes...these cannot breed with "normal" tree frogs, and within a two or three generations, there were two species where before there was one. No gradual change in response to the environment, just a sudden reproductive isolation leading (very quickly) to new species.
Still think macroevolution doesn't occur? Tell that to the tree frogs. (Don't worry; these particular species don't bite and aren't poisonous.)
 According to the creationists...
Macroevolution is a word beloved of anti-evolutionists but is little used in scientific circles. Anti-evolutionists consider it to mean evolution above the species level or the evolution of one species from another, something that science considers to be merely one aspect of evolution. Many creationists, and like-minded anti-evolutionists, will admit that microevolution, or adaptation, occurs, indeed they require it to be accelerated to extremes undreamt of by science in order to salvage their global flood/kinds theology, but will state emphatically that macroevolution is impossible, by giving straw man arguments like "A monkey can't give birth to a human".
 See also