What is macroevolution?
First, we have to get the definitions right. The following terms are defined: macroevolution, microevolution, cladogenesis, anagenesis, punctuated equilibrium theory, phyletic gradualism
Creationists often assert that "macroevolution" is not proven, even if "microevolution" is, and by this they seem to mean that whatever evolution is observed is microevolution, but the rest is macroevolution. In making these claims they are misusing authentic scientific terms; that is, they have a non-standard definition, which they use to make science appear to be saying something other than it is. Evolution proponents often say that creationists invented the terms. This is false. Both macroevolution and microevolution are legitimate scientific terms, which have a history of changing meanings that, in any case, fail to underpin creationism.
In science, macro at the beginning of a word just means "big", and micro at the beginning of a word just means "small" (both from the Greek words). For example, "macrofauna" means big animals, observable by the naked eye, while "microfauna" means small animals, which may be observable or may not without a microscope. Something can be "macro" by just being bigger, or there can be a transition that makes it something quite distinct.
In evolutionary biology today, macroevolution is used to refer to any evolutionary change at or above the level of species. It means at least the splitting of a species into two (speciation, or cladogenesis, from the Greek meaning "the origin of a branch", see Fig. 1) or the change of a species over time into another (anagenetic speciation, not nowadays generally accepted [note 1]). Any changes that occur at higher levels, such as the evolution of new families, phyla or genera, are also therefore macroevolution, but the term is not restricted to those higher levels. It often also means long-term trends or biases in evolution of higher taxonomic levels.
Microevolution refers to any evolutionary change below the level of species, and refers to changes in the frequency within a population or a species of its alleles (alternative genes) and their effects on the form, or phenotype, of organisms that make up that population or species. It can also apply to changes within species that are not genetic.
Another way to state the difference is that macroevolution is between-species evolution and microevolution is within-species evolution. Sometimes, macroevolution is called "supraspecific evolution" (Rensch 1959, see Hennig 1966: 223-225).
There are various views of the dynamics of macroevolution. Punctuated Equilibria are patterns of change that indicate stasis, or long periods of time where species exhibit very little change. There are several hypotheses that attempt to explain stasis. The current consensus among paleontologists is that large populations are buffered against evolutionary change by natural selection or genetic drift. Evolutionary change becomes easier when populations split into smaller demes. This change can be "locked in" if the subpopulations evolve reproductive isolation and become separate species. That's why change is associated with cladogenesis. Phyletic gradualism suggests that species continue to adapt to new challenges over the course of their history (see Fig. 1). Species selection and species sorting theories think that there are macroevolutionary processes going on that make it more or less likely that certain species will exist for very long before becoming extinct, in a kind of parallel to what happens to genes in microevolution.
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