Macroevolution

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Macroevolution is evolution on a scale of 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.^[3]

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 theropod dinosaurs.

Abrupt transformations from one biologic system to another, for example the passing of life from water into land or the transition from invertebrates to vertebrates, are rare. Few major biological types have emerged during the evolutionary history of life and most of them survive till today. When lifeforms take such giant leaps, they meet little to no competition and are able to exploit a plethora of available niches, following a pattern of adaptive radiation. This can lead to convergent evolution, where unrelated populations display similar adaptations.^[4]

The evolutionary course of Equidae (wide family including all horses and related animals) is often viewed as a typical example of macroevolution. The earliest known genus, Hyracotherium (now reclassified as a palaeothere), was a herbivore animal resembling a dog that lived in the early Cenozoic. As its habitat transformed into an open arid grassland, selective pressure required that the animal become a fast grazer. Thus elongation of legs and head as well as reduction of toes gradually occurred, producing the only extant genus of Equidae, Equus.^[4]

Origin of the term

Russian entomologist Yuri Filipchenko first coined the terms "macroevolution" and "microevolution" in 1927 in his German language work, "Variabilität und Variation". Since the inception of the two terms, their meanings have been revised several times and the term macroevolution fell into limited disfavour when it was taken over by such writers as the geneticist Richard Goldschmidt (1940) and the paleontologist Otto Schindewolf to describe their orthogenetic theories.^[5]

A more practical definition of the term describes it as changes occurring on geological time scales, in contrast to microevolution, which occurs on the timescale of human lifetimes.^[6] This definition reflects the spectrum between micro- and macro-evolution, whilst leaving a clear difference between the terms: because the geological record rarely has a resolution better than 10,000 years, and humans rarely live longer than 100 years, "meso-evolution" is never observed.^[6]

As a result, apart from Dobzhansky, Bernhard Rensch and Ernst Mayr, very few neo-Darwinian writers used the term, preferring instead to talk of evolution as changes in allele frequencies without mention of the level of the changes (above species level or below). Those who did were generally working within the continental European traditions (as Dobzhansky, Ernst Mayr, Bernhard Rensch, Richard Goldschmidt, and Otto Schindewolf were) and those who didn't were generally working within the Anglo-American tradition (such as John Maynard Smith and Richard Dawkins). Hence, use of the term "macroevolution" is sometimes wrongly used as a litmus test of whether the writer is "properly" neo-Darwinian or not.^[5]

Macroevolution and the modern evolutionary synthesis

Within the Modern Synthesis school of thought, macroevolution is thought of as the compounded effects of microevolution.^[7] Thus, the distinction between micro- and macroevolution is not a fundamental one – the only difference between them is of time and scale. As Ernst W. Mayr observes, "transspecific evolution is nothing but an extrapolation and magnification of the events that take place within populations and species...it is misleading to make a distinction between the causes of micro- and macroevolution”.^[7] However, time is not a necessary distinguishing factor – macroevolution can happen without gradual compounding of small changes; whole-genome duplication can result in speciation occurring over a single generation - this is especially common in plants.^[8]

Changes in the genes regulating development have also been proposed as being important in producing speciation through large and relatively sudden changes in animals' morphology.^[9][10]

Research topics

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

• Adaptive radiations such as The Cambrian Explosion.
• Changes in biodiversity through time.
• Genomic evolution, like horizontal gene transfer, genome fusions in endosymbioses, and adaptive changes in genome size.
• Mass extinctions.
• Speciation and extinction rates.
• The debate between punctuated equilibrium and gradualism.
• The role of development in shaping evolution, particularly such topics as heterochrony and phenotypic plasticity.
• At present-day there is developping an interdisciplinary approach which aims at considering macroevolution at a transdisciplinary scale, and concentrates on the comparison between biological and social macroevolution as this gives new significant possibilities to understand peculiarities of each of the two types of macroevolution.^[11]

Misuse

Main article: Objections to evolution

See also: Speciation

The term "macroevolution" frequently arises within the context of the evolution/creation debate, usually used by creationists alleging a significant difference between the evolutionary changes observed in field and laboratory studies and the larger scale macroevolutionary changes that scientists believe to have taken thousands or millions of years to occur. They may accept that evolutionary change is possible within species ("microevolution"), but deny that one species can evolve into another ("macroevolution").^[1] Contrary to this belief among the anti-evolution movement proponents, evolution of life forms beyond the species level ("macroevolution", i.e. speciation in a specific case) has indeed been observed multiple times under both controlled laboratory conditions and in nature.^[12] The claim that macroevolution does not occur, or is impossible, is thus demonstrably false and without support in the scientific community.

Such claims are rejected by the scientific community on the basis of ample evidence that macroevolution is an active process both presently and in the past.^[5][13] The terms macroevolution and microevolution relate to the same processes operating at different scales, but creationist claims misuse the terms in a vaguely defined way which does not accurately reflect scientific usage, acknowledging well observed evolution as "microevolution" and denying that "macroevolution" takes place.^[5][14] Evolutionary theory (including macroevolutionary change) remains the dominant scientific paradigm for explaining the origins of Earth's biodiversity. Its occurrence is not disputed within the scientific community.^[15] 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".^[16][17]

Nicholas Matzke and Paul R. Gross have accused creationists of using "strategically elastic" definitions of micro- and macroevolution when discussing the topic.^[1] The actual definition of macroevolution accepted by scientists is "any change at the species level or above" (phyla, group, etc.) and microevolution is "any change below the level of species." Matzke and Gross state that many creationist critics define macroevolution as something that cannot be attained, as these critics describe any observed evolutionary change as "just microevolution".^[1]

See also

• List of transitional fossils
• Transitional fossil
• Microevolution
• Speciation

References

1. ^ ^{a b c d} Matzke, Nicholas J. and Paul R. Gross. 2006. Analyzing Critical Analysis: The Fallback Antievolutionist Strategy. In Eugenie Scott and Glenn Branch, Not in Our Classrooms: Why Intelligent Design is Wrong for Our Schools, Beacon Press, Boston ISBN 0807032786^{[page needed]}
2. ^ Dobzhansky, Theodosius Grigorievich (1937). Genetics and the origin of species. New York: Columbia Univ. Press. p. 12. LCCN 37033383. 
3. ^ Reznick DN, Ricklefs RE (February 2009). "Darwin's bridge between microevolution and macroevolution". Nature 457 (7231): 837–42. doi:10.1038/nature07894. PMID 19212402. 
4. ^ ^{a b} Introduction to Ecology (1983) - J.C. Emberlin, chapter 8
5. ^ ^{a b c d} Macroevolution: Its definition, Philosophy and History
6. ^ ^{a b} Gingerich, P. D. (1987). "Evolution and the fossil record: patterns, rates, and processes". Canadian Journal of Zoology 65 (5): 1053–1060. doi:10.1139/z87-169.  edit
7. ^ ^{a b} Kutschera U, Niklas KJ (June 2004). "The modern theory of biological evolution: an expanded synthesis". Die Naturwissenschaften 91 (6): 255–76. doi:10.1007/s00114-004-0515-y. PMID 15241603. 
8. ^ Rieseberg LH, Willis JH (August 2007). "Plant Speciation". Science 317 (5840): 910–4. doi:10.1126/science.1137729. PMC 2442920. PMID 17702935. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2442920. 
9. ^ Valentine JW, Jablonski D (2003). "Morphological and developmental macroevolution: a paleontological perspective". The International Journal of Developmental Biology 47 (7–8): 517–22. PMID 14756327. http://www.intjdevbiol.com/paper.php?doi=14756327. 
10. ^ Johnson NA, Porter AH (2001). "Toward a new synthesis: population genetics and evolutionary developmental biology". Genetica 112-113: 45–58. doi:10.1023/A:1013371201773. PMID 11838782. 
11. ^ Grinin, L., Markov, A. V., Korotayev, A. Aromorphoses in Biological and Social Evolution: Some General Rules for Biological and Social Forms of Macroevolution / Social evolution & History, vol.8, num. 2, 2009 [1]
12. ^ Rice, W.R.; Hostert (1993). "Laboratory experiments on speciation: what have we learned in 40 years". Evolution 47 (6): 1637–1653. doi:10.2307/2410209. JSTOR 2410209. 
    *Jiggins CD, Bridle JR (2004). "Speciation in the apple maggot fly: a blend of vintages?". Trends Ecol. Evol. (Amst.) 19 (3): 111–4. doi:10.1016/j.tree.2003.12.008. PMID 16701238. 
    *Boxhorn, J (1995). "Observed Instances of Speciation". TalkOrigins Archive. http://www.talkorigins.org/faqs/faq-speciation.html. Retrieved 2008-12-26. 
    *Weinberg JR, Starczak VR, Jorg, D (1992). "Evidence for Rapid Speciation Following a Founder Event in the Laboratory". Evolution 46 (4): 1214–20. doi:10.2307/2409766. JSTOR 2409766. 
    *Kirkpatrick, Mark; Virginie Ravigné (2002-03). "Speciation by Natural and Sexual Selection: Models and Experiments". The American Naturalist 159 (3): S22–S35. doi:10.1086/338370. ISSN 00030147. JSTOR 3078919. PMID 18707367. 
13. ^ CB901: No Macroevolution
14. ^ CB902: Microevolution is distinct from macroevolution.
15. ^ Myers 2006; NSTA 2007; IAP 2006; AAAS 2006; and Pinholster 2006; Ruling, Kitzmiller v. Dover page 83
16. ^ 29+ Evidences for Macroevolution: The Scientific Case for Common Descent, Douglas L. Theobald, TalkOrigins Archive, Vers. 2.83, 2004, 12 Jan, 2004.
17. ^ Laurence Moran (1993). "Evolution is a Fact and a Theory". TalkOrigins Archive. http://www.talkorigins.org/faqs/evolution-fact.html. Retrieved 2008-02-07. 

External links

• Introduction to macroevolution
• Macroevolution as the common descent of all life
• Macroevolution in the 21st Century Macroevolution as an independent discipline.
• Macroevolution FAQ