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Macroevolution

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Macroevolution is a purely theoretical biological process thought to produce relatively large (macro) evolutionary change within biological organisms. The term is used in contrast to minor (microevolution) changes, and is most commonly defined as "evolution above the species level". Macroevolution can not be observed directly, but is instead studied through the examination of fossils (paleontology) and the similarities and differences in the anatomy of organisms (comparative morphology).[1]

It is thought to provide the mechanism by which an original taxa (i.e. phylum or class) may change enough to result in newly descendant phyla or classes. The development of new taxonomic groups requires new types of structures (morphology) and functions.[2]

The concept of macroevolution was introduced due to the absence of transitional forms between higher taxa (i.e. phyla, classes), which is in stark contrast to the expectations of Darwinian gradualism. It was therefore proposed as a mechanism responsible for large-scale patterns of evolution, which are distinct from the genetic and small-scale factors that contribute to gradual change within populations. These smaller scale changes are those defined as microevolution.[3]

Macroevolutionary theory is based on several fundamental axioms.

  1. Species continuity: that evolution produces a functional continuum linking all species together.
  2. Common descent: that all lifeforms have descended from a single primeval cell.
  3. Randomness: that all adaptive design is the result of blind, random processes. [4]

Contents

History

Main Article: History of evolutionism
Charles Darwin's notebook showing sketch of phylogenetic tree. Note the words I think at the top of the notebook.

In Charles Darwin's book The Origin of Species (1859), he presents two theories, which are often called the Special and General theories of evolution. The special theory is relatively restrictive in scope and proposes that new species form through the process of natural selection. The general theory postulates that all of the diversity of life on Earth can be attributed to this process by simple extrapolation.[5] These two Darwinian theories describe what is now commonly referred to as micro and macroevolution respectively.[2]

The terms macroevolution and microevolution were first used by evolutionary Russian entomologist Iurii Filipchenko in a 1927 book titled Variabilitat und Variation. He asserted that micro- and macroevolution were processes involving different mechanisms and caliber. The terms were later introduced to English-speaking biological community in 1937 by Filipchenko's former student Theodosius Dobzhansky in Genetics and the Origin of Species.

In the late 1930s, Dobzhansky helped devise the modern evolutionary synthesis, a neodarwinian view that attempted to reconcile Darwinism with mendelian genetics.[6] The modern synthesis accepted as one of its basic tenets the proposal that all evolution was best explained by a simple extrapolation from micro to macro-evolution. It was asserted that there is no fundamental distinction made between micro and macroevolution[7]

It should, however, be noted that Dobzhansky argued with reluctance against the differentiation of macro and microevolution; writing "we are compelled at the present level of knowledge reluctantly to put a sign of equality between the mechanisms of macro- and microevolution" [8]. While some have suggested that his hesitancy to equate macro and microevolution was because it went against the beliefs of his mentor,[6] it is also certain that Dobzhansky was aware of the long recognized difficulty in relying exclusively on the explanatory power of microevolution as the sole agent of evolution.

Absence of intermediates

Main Article: Transitional forms

Darwin assumed that all evolution was merely an extension of the same process occurring within populations.[9] However, he also assumed that the continuum of species his theory required, but which were obtrusively absent from living populations, would be discovered following further paleontological excavations.[10] Darwin himself admitted the absence of this crucial evidence in The Origin of Species.

Geological research, though it has added numerous species to existing and extinct genera, and has made the intervals between some few groups less wide than they otherwise would have been, yet has done scarcely anything in breaking the distinction between species, by connecting them together by numerous, fine, intermediate varieties; and this not having been affected is probably the gravest and most obvious of all the many objections which may be urged against my views.[11]

The introduction of a 2-part evolutionary mechanism (micro vs. macro) was prompted by subsequent observations that the fossil records illustrated the same discontinuous trends found in living population. The absence of species continuity is in stark contrast to the expectations of Darwinian evolution, which proposed a slow and gradual process expected to render a continuous series of species as they evolved from one taxa to the next.

Contrary to Darwinian expectations, organisms are found to comprise very distinct groups between which exists a sheer absence of transitional forms. Michael Denton, an evolutionist, acknowledges in his book Evolution: A Theory in Crisis that the central problem with Darwinism is that no direct empirical evidence exists in the way of a continuous series of intermediates between taxa.

There is no doubt that as far as his macroevolutionary claims were concerned Darwin's central problem in the Origin lay in the fact that he had absolutely no direct empirical evidence in the existence of clear-cut intermediates that evolution on a major scale had ever occurred and that any of the major divisions of nature had been crossed gradually through a sequence of transitional forms.[12]

To nearly all of the great biologists and naturalists of the late eighteenth and early nineteenth, Darwin's theory failed to explain the discontinuity of species. Instead a typological model was adhered to, which recognized that organisms exist as distinct types.[13] An uncharacterized macroevolution process was then proposed as being responsible for the rapid saltation (evolutionary jumps) responsible for the gaps between taxa, with the traditional micro process operating to produce the slow and gradual change responsible for groups of similar species.

Extrapolation of microevolution

Main Article: Microevolution

Although paleontology has still not been able to demonstrate the transitional forms necessary to be vindicate Darwin's theory, proponents of the modern evolutionary synthesis accepted as one of its basic tenets the proposal that all evolution was best explained by a simple extrapolation from micro to macro-evolution.[7] Many modern evolutionary biologists now assert that macroevolution is the result of the compounded effects of microevolution. It is claimed there is no fundamental distinction made between micro and macroevolution, with the only difference between them as one of time and scale.[14]

The claim that macroevolution is simply an extrapolation of microevolution causes the term to have two distinct meanings and to be used variably within literature. The following two definitions of macroevolution by the Talk.Origins Archive readily illustrate that evolutionists define the term differently and remain in debate particularly regarding whether speciation should be considered a part of macro of microevolution. Note that in one instance below macroevolution is defined as the process able to produce large scale functional and structural changes, and then subsequently as being virtually indistinguishable from microevolution (evolution at the species level).

Talk.Origins Archive Definitions:

  • Evolution on the grand scale resulting in the origin of higher taxa. In evolutionary theory it thus entails common ancestry, descent with modification, the genealogical relatedness of all life, transformation of species, large scale functional and structural changes, etc.[15]
  • Evolution at or above the species level. The boundary between macro- and micro- is fuzzy, as some researchers prefer to include speciation in micro- and others reason that the only macro- process that gives distinctive events is speciation. Speciation events are thus, to many scientists, examples of macroevolution.[16]

Controversy among evolutionists

Despite the acceptance by some evolutionists that macroevolution is simply an extrapolation of the process of microevolution, many hold strong reservations, and assert that large-scale evolutionary phenomena cannot be explained by processes observed at the level of populations.[17] Evolutionists continue to debate whether the Darwinian mechanisms of change, which rests on the tenets of gradualism and natural selection, can explain the discontinuous nature of evolution. Many eminent evolutionists such as Steven Gould, Ivan Schmalhausen, Steven M. Stanley, and C. H. Waddington, hold that microevolution and macroevolution represent fundamentally different processes.[6]

New concepts and information from molecular, developmental biology, systematics, geology and the fossil record of all groups of organisms, need to be integrated into an expanded evolutionary synthesis. These fields of study show that large-scale evolutionary phenomena cannot be understood solely on the basis of extrapolation from processes observed at the level of modern populations and species. Patterns and rates of evolution are much more varied than had been conceived by Darwin or the evolutionary synthesis, and physical factors of the earth's history have had a significant, but extremely varied, impact on the evolution of life."[18]

The eminent evolutionist Ernst Mayr, who some consider the father of modern evolutionary biology, also acknowledges that one reason this controversy continues is because gradual transitions are not evident in the fossil record or even between living biota, but rather discontinuities are "overwhelmingly frequent."[19] If evolution were gradual and continuous, one would expect to find transitions between taxa. Yet, there is no intermediary between whales and terrestrial mammals, nor between reptiles and mammals, nor reptiles and birds, nor flowering plants and their nearest relatives. Indeed, all phyla of animals are separated by a gap. Likewise, the fossil record shows striking discontinuities, with new species appearing suddenly. Evolutionists offer explanations for such phenomena, such as the incomplete sampling that results from the fossil record, but the very presence of such gaps is one reason for the controversy.[6]

Punctuated equilibrium

Main Article: Punctuated equilibrium

The insistence that macroevolutionary phenomena be explained by microevolutionary extrapolation was largely due to the absence of other credible mechanisms. The absence of transitional forms calls for a mechanism whereby organisms can change in jumps (saltationism). As the Darwinian mechanism is reliant upon slow and gradual change acting within populations, like Darwin, modern evolutionists found themselves without a credible mechanism and therefore held to microevolution as capable of producing all evolutionary change.

In recent years, Steven Gould and Niles Eldredge have put forth another mechanism to explain the absence of transitional forms, known as punctuated equilibrium. They assert that the discontinuous nature of populations and fossil records is due to long periods of morphological stability (equilibrium) interspersed by short periods of evolutionary change (punctuation).[6]

Creationist perspective

The common modernized definition for macroevolution is, "the evolution of higher taxa". In other words, it results in the formation of new taxonomic groups. Creationists acknowledge that given enough time, the process of evolution will eventually lead to the development of groups of related species (i.e new genera). For example, macroevolution is used when describing the theoretical evolution of all arthropods from some ancient ancestral species. In contrast to this position, the creationists believe this scale of evolution has never taken place, but instead assert that there are many baramin or created kinds within the phylum Arthropoda.

Evolutionists use macroevolution to propose an evolutionary relationship between organisms that are vastly different, and in fact claim that the process is responsible for the common descent of all organisms on Earth. Creationists are fond of saying that in reality this is not unlike the fairy tale of a frog turning into a prince (albeit stretched over a long period of time). It is also said that evolutionists remain unable to provide any empirical evidence that a new plant or animal species have ever produced new types of novel structures or functions which are totally lacking in the ancestral species.

Evolutionary boundary

Evolutionary Boundary refers to a limitation of macroevolutionary potential, shown by a series of mathematical simulations in which immediate competition is distinguished from long-term major-biological-change competition.

Much of the credibility of Darwin's General Theory of Evolution is based upon a generalized idea of Natural Selection acting upon populations. Neo-Darwinism involves mutational changes that have been theorized to have caused sub-populations to develop differences which, when combined with later mutational changes, eventually add up to major transformations. The generalization is in mixing the idea of immediate survivability with the idea of long-term benefits of new organs or other biological structures.

In reality, when an organism experiences a mutational change, there are three relevant results possible: Immediate competitiveness is increased, the beginning of a new biological structure is started (or continued), or there is a combination of the first two. Any major change must occur in stages, and this can be calculated with simple formulas.

According to Jonathan Whitcomb, it is the number of reproductive cycles (how many times reproduction occurs), rather than how long life has existed, that allows any potential credibility for macroevolution. His simulations, with an original population of 1029, showed that no major step in macroevolutionary development could reasonably take place. Natural Selection, according to his calculations, makes macroevolution practically impossible, even in a simulated environment more ideal than any natural environment presently found on the earth. "Survival of the Fittest" actually prevents any major change in biology.[20]

Use of the term

Regarding macroevolution, there are at least three perspectives regarding the use of the term within the creation community.

Never Happened
It is frequently claimed by creationists that microevolution happens, but macroevolution does not. The quantity of evolution creationists agree with is frequently called "variation within a kind", which is believed to be synonymous with the term microevolution. The claims of evolutionists that all life on earth has descended from a single ancestral cell is frequently equated with the term macroevolution further adding to this view.

Describes the Kind History
Creationists acknowledge that each Biblical kind has undergone many speciation event, which subsequently adapted to various environments thereby producing many new and diverse species since the creation. It is also readily accepted that many species went extinct during the flood of Noah, and only a single species from some kinds was spared from the flood. Subsequently, each of these species has evolved or diversified since the flood into a great many distinct genera, each with many new species.

Some argue, based on the modern usage of the word macroevolution, that the term describes the evolutionary history of each Biblical kind. Furthermore, it may be true that many evolutionists would define such a history of extinction, speciation, and diversification as macroevolution. Therefore, by outright denying the occurrence of macroevolution without clarification as it the intended meaning of the word, a creationists may well be rejecting a quantify of adaptive change that is otherwise acknowledged to have taken place.[21]

Avoid Usage
While either use of microevolution or macroevolution by creationists might be true for some specific examples, as a general rule, the use of these terms should be done with care. Many creationists caution against using either term on the grounds that they detract from the real issue, the gain or loss of information, and are misleading in talking about the size of the change instead of the direction of the change.[22]

Definitions

  • The evolution of higher taxa.(i.e. new Phyla, Classes, Orders, or Families).
  • Evolution at or above the species level. The boundary between macro- and micro- is fuzzy, as some researchers prefer to include speciation in micro- and others reason that the only macro- process that gives distinctive events is speciation. Speciation events are thus, to many scientists, examples of macroevolution.[16]
  • Evolution on the grand scale resulting in the origin of higher taxa. In evolutionary theory it thus entails common ancestry, descent with modification, the genealogical relatedness of all life, transformation of species, large scale functional and structural changes, etc.[15]
  • The origin of new large-scale features such as organs or body plans.[23]
  • Evolution on a large scale extending over geologic era and resulting in the formation of new taxonomic groups.[24]
  • Large-scale patterns or processes in the history of life, including the origins of novel organismal designs, evolutionary trends, adaptive radiations and extinctions.[3]
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References

  1. Minkoff, Eli C. Evolutionary Biology, Addison-Wesley Publishing Company, 1983. p264.
  2. 2.0 2.1 Evolution is Partly True by R. Totten
  3. 3.0 3.1 macroevolution, from Wiktionary
  4. Denton, Michael. Evolution: A Theory in Crisis. Adler & Adler. 1986, p345
  5. Denton, p44
  6. 6.0 6.1 6.2 6.3 6.4 Macroevolution entry from New World Encyclopedia
  7. 7.0 7.1 wikipedia:Modern evolutionary synthesis
  8. Dobzhansky, T. 1937. Genetics and the Origin of Species. New York, NY: Columbia University Press
  9. Denton, p86
  10. Denton, p158
  11. Darwin, C. (1872) The Origin of Species, 6th ed, 1962, Collier Books, New your, p462.
  12. Denton, p56
  13. Denton, p99
  14. wikipedia:Macroevolution
  15. 15.0 15.1 Macroevolution Glossary from evcforum.net
  16. 16.0 16.1 macroevolution entry in Talk.Origins Jargon File
  17. Denton, p86-88
  18. Carroll, Robert L., "Towards a new evolutionary synthesis," Trends in Ecology and Evolution, 2000, Vol. 15, pp.27-32, p.27
  19. Mayr, E. 2001. What Evolution Is. New York, NY: Basic Books.
  20. An Evolutionary Boundary: Testing the Potential for A Change in Energy Source In Simple Organisms by Jonathan Whitcomb
  21. Evolution; God's Greatest Creation by Chris Ashcraft, published by NWCreation.net
  22. Variation, information and the created kind by Dr. Carl Wieland. TJ 5(1):42–47. April 1991
  23. Glossary of Explore Evolution
  24. Macroevolution at Princeton University's Wordnet

External links

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