Microevolution and macroevolution are different things, but they
involve mostly the same processes. Microevolution is defined as the
change of allele frequencies (that is, genetic variation due to
processes such as selection, mutation, genetic drift, or even
migration) within a population. There is no argument that
microevolution happens (although some creationists, such as Wallace,
deny that mutations happen). Macroevolution is defined as evolutionary
change at the species level or higher, that is, the formation of new
species, new genera, and so forth. Speciation has also been
observed.
Creationists have created another category for which they use the word
"macroevolution." They have no technical definition of it, but in
practice they use it to mean evolution to an extent great enough that
it has not been observed yet. (Some creationists talk about
macroevolution being the emergence of new features, but it is not clear
what they mean by this. Taking it literally, gradually changing a
feature from fish fin to tetrapod limb to bird wing would not be
macroevolution, but a mole on your skin which neither of your parents
have would be.) I will call this category supermacroevolution to avoid
confusing it with real macroevolution.
Speciation is distinct from microevolution in that speciation usually
requires an isolating factor to keep the new species distinct. The
isolating factor need not be biological; a new mountain range or the
changed course of a river can qualify. Other than that, speciation
requires no processes other than microevolution. Some processes such
as disruptive selection (natural selection that drives two states of
the same feature further apart) and polyploidy (a mutation that
creates copies of the entire genome), may be involved more often in
speciation, but they are not substantively different from
microevolution.
Supermacroevolution is harder to observe directly. However, there is
not the slightest bit of evidence that it requires anything but
microevolution. Sudden large changes probably do occur rarely, but
they are not the only source of large change. There is no reason to
think that small changes over time cannot add up to large changes,
and every reason to believe they can. Creationists claim that
microevolution and supermacroevolution are distinct, but they have
never provided an iota of evidence to support their claim.
There is evidence for supermacroevolution in the form of progressive
changes in the fossil record and in the pattern of similarities among
living things showing an absence of distinct "kinds." This evidence
caused evolution in some form to be accepted even before Darwin
proposed his theory.
