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Macroevolution is generally understood to be the process of speciation, and in particular, cladogenesis—the bifurcating or branching pattern of evolution whereby an ancestral taxon diverges over time and apomorphies appear and is generally thought to be evolution above the species level. The vast majority of speciation is allopatric, occurring in isolated populations peripheral to a main population (Mayr 1942, 1982, Carroll 1988). Such events can take place at varying rates, from bradytelyic, to horotelyic, and tachytelyic (Simpson 1944).
Macroevolution is the part of evolution that creationists are not willing to accept. Most Creationists accept microevolution, which they define as evolution within kinds (kinds meaning sometimes species, sometimes bigger taxa, depending on which type of creationist, creationist organization, or individual creationist that you ask) but deny that one kind may evolve into another (macroevolution). This argument is strongly opposed by scientists because microevolution and macroevolution are the same process in different scales and it is irrational to say that only one of them exists.
According to Douglas Futuyma, speciation and thus macroevolution was already observed by Dobzhansky and Pavlovyks (Dobzhansky, Pavlovyks, 1971, Nature 23, 1971, 289-292) in laboratory on the fly species Drosophila paulistorum. A strain which was isolated for several years in the laboratory could no longer interbreed with other strains of Drosophila paulistorum.