Macroevolution comprises the evolutionary processes and patterns which occur at and above the species level.
Macroevolution addresses the evolution of species and higher taxonomic groups (genera, families, orders, etc) and uses evidence from phylogenetics,
Origin and changing meaning of the term
After
Charles Darwin published his book
On the Origin of Species in 1859, evolution was widely accepted to be real phenomenon. However, many scientists still disagreed with Darwin that natural selection was the primary mechanism to explain evolution. Prior to the modern synthesis, during the period between the 1880s to the 1930s (dubbed the 'Eclipse of Darwinism') many scientists argued in favor of alternative explanations. These included '
orthogenesis', and among its proponents was the Russian entomologist
Yuri Filipchenko.
Filipchenko appears to have been the one who coined the term 'macroevolution' in his book Variabilität und Variation (1927).
Filipchenko's also claimed that a new taxon cannot evolve from an older one with a lower rank; e.g. a species cannot evolve into a family. It must originate from a preceding family. Furthermore, the evolution of a new family must require the sudden appearance of new traits which are different in greater magnitude compared to the new traits required for the evolution of a genus or species.
However, Filipchenko's views are not consistent with contemporary understanding of evolution. Furthermore, the Linnaean ranks of 'genus' (and higher) are not real entities but arbitrary concepts. These traditional taxonomic concepts break down when they are applied to common ancestry.
Nevertheless, Filipchenko’s distinction between microevolution and macroevolution had a major influence on evolutionary biology. The term macroevolution was adopted by Filipchenko's protégé Theodosius Dobzhansky in his book 'Genetics und the Origin of Species' (1937), a seminal piece that contributed to the development of the Modern Synthesis. The term was also used by critics of the Modern Synthesis. A good example of this is the book The Material Basis of Evolution (1940) by the geneticist Richard Goldschmidt, a close friend of Filipchenko.
As an alternative to saltational evolution, Dobzhansky
Microevolution vs Macroevolution
Micro- and macroevolution are both supported by overwhelming evidence. This fact remains uncontroversial within the scientific community. However, there has been considerable debate regarding the connection between microevolution and macroevolution.
Broadly speaking, there are two views regarding this issue. The 'Extrapolation' view holds that macroevolution is merely cumulative microevolution. The 'Decoupled' view holds that there are separate macroevolutionary processes that cannot be sufficiently explained by microevolutionary processes alone. Most scientists who adopt the second viewpoint are not claiming that macroevolution is incompatible with microevolution. Rather, they see macroevolution as an autonomous field of study regarding the deep history of life. For this reason, a full understanding of macroevolution requires insights that are not limited to microevolution.
Microevolution is characterized by the evolutionary process of changing heritable characteristics (phenotypes) and changes in allele frequencies (genotypes) within populations. This involves mechanisms such as mutation, natural selection, and genetic drift as studied in the field of population genetics.
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How different species are related to each other is researched in phylogenetics).
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The rates of evolutionary change and across time in the fossil record.
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Why different taxonomic groups (even those with similar ages) exhibit different survival/extinction rates, species diversity, and/or morphological disparity.
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The causes and impacts of Mass extinctions and evolutionary diversifications,
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Does natural selection also operate at the species level (see Group selection)?
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Long-term trends in evolution, e.g. trends towards complexity or simplicity and whether these trends are directional or passive.
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How distinctive and complex traits have evolved, e.g. gene duplication, heterochrony, novelty in evo-devo, facilitated variation, and constructive neutral evolution.
Macroevolutionary processes
Speciation
According to Hautmann
, speciation has both micro- and macroevolutionary aspects. Specifically, speciation also involves the classic process of descent with modification, i.e. morphological transformation observed across many generations. This is microevolutionary. In contrast, the species variation produced by speciation, and the rate at which it successfully occurs, is macroevolutionary.
Stephen J. Gould also saw species as the basic unit of macroevolution.
Speciation is the process in which populations within one species change to an extent at which they become reproductively isolated, that is, they cannot interbreed anymore. However, this classical concept has been challenged and more recently, a phylogenetic or evolutionary species concept has been adopted. Their main criteria for new species is to be diagnosable and Monophyly, that is, they form a clearly defined lineage.
Charles Darwin first discovered that speciation can be extrapolated so that species not only evolve into new species, but also into new Genus, families and other groups of animals. In other words, macroevolution is reducible to microevolution through selection of traits over long periods of time.
According to the Resource-use hypothesis, the diversification of terrestrial species is closely related to global climatic changes, particularly the Cenozoic alternation of warming and cooling episodes. Global analysis of terrestrial mammals supports the view that these physical environmental changes have shaped macroevolutionary patterns by promoting biome specialisation. This specialization leads to significantly higher rates of vicariance and speciation in biome specialist (stenobiomic) lineages compared to generalist lineages.
Evolution of new organs and tissues
One of the main questions in evolutionary biology is how new structures evolve, such as new organs. Macroevolution is often thought to require the evolution of structures that are 'completely new'. However, fundamentally novel structures are not necessary for dramatic evolutionary change. As can be seen in
Vertebrate, most "new" organs are actually not new—they are simply modifications of previously existing organs. For instance, the evolution of
mammal diversity in the past 100 million years has not required any major innovation.
All of this diversity can be explained by modification of existing organs, such as the evolution of
Tusk from
. Other examples include
Bird wing (modified limbs),
(modified
),
(modified
, e.g. found in
fish),
or even the
heart (a muscularized segment of a
vein).
The same concept applies to the evolution of "novel" tissues. Even fundamental tissues such as bone can evolve from combining existing (collagen) with calcium phosphate (specifically, Hydroxyapatite). This probably happened when certain cells that make collagen also accumulated calcium phosphate to get a proto-bone cell.
Examples
Evolutionary faunas
A macroevolutionary benchmark study is Sepkoski's
work on marine animal diversity through the Phanerozoic. His iconic diagram of the numbers of marine families from the Cambrian to the Recent illustrates the successive expansion and dwindling of three "evolutionary faunas" that were characterized by differences in origination rates and carrying capacities. Long-term ecological changes and major geological events are postulated to have played crucial roles in shaping these evolutionary faunas.
Stanley's rule
Macroevolution is driven by differences between species in origination and extinction rates. Remarkably, these two factors are generally positively correlated: taxa that have typically high diversification rates also have high extinction rates. This observation has been described first by Steven Stanley, who attributed it to a variety of ecological factors.
Yet, a positive correlation of origination and extinction rates is also a prediction of the Red Queen hypothesis, which postulates that evolutionary progress (increase in fitness) of any given species causes a decrease in fitness of other species, ultimately driving to extinction those species that do not adapt rapidly enough.
High rates of origination must therefore correlate with high rates of extinction.
Stanley's rule, which applies to almost all taxa and geologic ages, is therefore an indication for a dominant role of biotic interactions in macroevolution.
Evolution of multicellularity
The evolution of multicellular organisms is one of the major breakthroughs in evolution. The first step of converting a unicellular organism into a
Animal (a multicellular organism) is to allow cells to attach to each other. This can be achieved by one or a few
. In fact, many
bacteria form multicellular assemblies, e.g.
cyanobacteria or
myxobacteria. Another species of bacteria,
Jeongeupia sacculi, form well-ordered sheets of cells, which ultimately develop into a bulbous structure.
Similarly, unicellular yeast cells can become multicellular by a single mutation in the ACE2 gene, which causes the cells to form a branched multicellular form.
Evolution of bat wings
The wings of
have the same structural elements (bones) as any other five-fingered mammal (see
Limb development). However, the finger bones in bats are dramatically elongated, so the question is how these bones became so long. It has been shown that certain growth factors such as bone morphogenetic proteins (specifically Bmp2) is over expressed so that it stimulates an elongation of certain bones. Genetic changes in the bat genome identified the changes that lead to this phenotype and it has been recapitulated in mice: when specific bat DNA is inserted in the mouse genome, recapitulating these mutations, the bones of mice grow longer.
Limb loss in lizards and snakes
evolved from
.
Phylogenetics analysis shows that snakes are actually nested within the phylogenetic tree of lizards, demonstrating that they have a common ancestor.
This split happened about 180 million years ago and several intermediary
are known to document the origin. In fact, limbs have been lost in numerous clades of
, and there are cases of recent limb loss. For instance, the
skink genus
Lerista has lost limbs in multiple cases, with all possible intermediary steps, that is, there are species which have fully developed limbs, shorter limbs with 5, 4, 3, 2, 1 or no toes at all.
Human evolution
While human evolution from their primate ancestors did not require massive morphological changes, our brain has sufficiently changed to allow human consciousness and intelligence. While the latter involves relatively minor morphological changes it did result in dramatic changes to
Brain.
Thus, macroevolution does not have to be morphological, it can also be functional.
The study of human (brain) evolution benefits from the fact that Human genome and ape genomes are available so that the genomes of our common ancestor can be reconstructed.
Evolution of viviparity in lizards
Most lizards are egg-laying and thus need an environment that is warm enough to incubate their eggs. However, some species have evolved
viviparity, that is, they give birth to live young, as almost all
do. In several clades of lizards, egg-laying (oviparous) species have evolved into live-bearing ones, apparently with very little genetic change. For instance, a European common lizard,
Zootoca vivipara, is viviparous throughout most of its range, but oviparous in the extreme southwest portion.
That is, within a single species, a radical change in reproductive behavior has happened. Similar cases are known from South American lizards of the genus
Liolaemus which have egg-laying species at lower altitudes, but closely related viviparous species at higher altitudes, suggesting that the switch from oviparous to viviparous reproduction does not require many genetic changes.
Research topics
Subjects studied within macroevolution include:
[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]]
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Adaptive radiations such as the Cambrian Explosion.
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Changes in biodiversity through time.
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Evo-devo (the connection between evolution and developmental biology)
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Genome evolution, like horizontal gene transfer, genome fusions in endosymbioses, and adaptive changes in genome size.
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Extinction event.
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Estimating diversification rates, including rates of speciation and extinction.
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The debate between punctuated equilibrium and gradualism.
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The role of development in shaping evolution, particularly such topics as heterochrony and phenotypic plasticity.
See also
Notes
Further reading
External links
