Macroevolution

Macroevolution is a scale of analysis of evolution in separated gene pools.^[1] Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution,^[2] which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population. The process of speciation may fall within the purview of either, depending on the forces thought to drive it. Paleontology, evolutionary developmental biology, comparative genomics and genomic phylostratigraphy contribute most of the evidence for the patterns and processes that can be classified as macroevolution. An example of macroevolution is the appearance of feathers during the evolution of birds from one group of dinosaurs.

Within the Modern Synthesis school of thought, macroevolution is thought of as the compounded effects of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one - the only difference between them is of time and scale. This understanding is disputed by some biologists, who claim that there may be macroevolutionary processes that cannot be described by strictly gradual phenotypic change, of the type studied by classical population genetics.

Some creationists have also adopted the term "macroevolution" to describe the form of evolution that they reject. They may accept that evolutionary change is possible within species ("microevolution"), but deny that one species can evolve into another ("macroevolution").^[1] These arguments are rejected by mainstream science, which holds that there is ample evidence that macroevolution has occurred in the past.^[3][4]

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Research topics

Some examples of subjects whose study falls within the realm of macroevolution:

• The debate between punctuated equilibrium and gradualism
• Speciation and extinction rates
• Mass extinctions
• Adaptive radiations such as The Cambrian Explosion
• Changes in biodiversity through time
• The role of development in shaping evolution, particularly such topics as heterochrony and developmental plasticity
• Genomic evolution, like horizontal gene transfer, genome fusions in endosymbioses, and adaptive changes in genome size

Origin of the Term

Russian Entomologist Yuri Filipchenko (or Philipchenko, depending on the transliteration) first coined the terms "macroevolution" and "microevolution" in 1927 in his German language work, "Variabilität und Variation"^[3].

Since the inception of the two terms, their meanings have been revised several times and even fallen into disfavour amongst scientists who prefer to speak of biological evolution as one process.^[3]

Response to criticisms of macroevolution

While details of macroevolution are continuously studied by the scientific community, the overall theory behind macroevolution (i.e. common descent) has been overwhelmingly consistent with empirical data. Predictions of empirical data from the theory of common descent have been so consistent that biologists often refer to it as the "fact of evolution" (Theobald 2004). Nevertheless, macroevolution is sometimes disputed by religious groups. Generally speaking, these groups attempt to differentiate between microevolution and macroevolution, asserting various hypotheses which are considered to have no scientific basis by any mainstream scientific organization, including the American Association for the Advancement of Science^[5].

When discussing the topic, creationists use "strategically elastic" definitions of micro- and macroevolution.^[1] Macroevolution, by their definition, cannot be attained. Any observed evolutionary change is described by them as being "just microevolution".^[1]

See also

• Transitional fossil
  • List of transitional fossils

References