Difference between revisions of "Evolution"
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===Speciation=== | ===Speciation=== | ||
| − | [[Speciation]] is the process where a species diverges into two or more descendant species. | + | [[Speciation]] is the process where a species diverges into two or more descendant species. (Perspective: models of speciation: what have we learned in 40 years? journal=Evolution |volume=57 |issue=10 ) It has been observed multiple times under both controlled laboratory conditions and in nature.(Jiggins CD, Bridle JR |title=Speciation in the apple maggot fly: a blend of vintages?) [http://www.talkorigins.org/faqs/faq-speciation.html]| In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.(Hoskin CJ, Higgle M, McDonald KR, Moritz C , Reinforcement drives rapid allopatric speciation, Nature) |
| − | The second mechanism of speciation is [[peripatric speciation]], which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the [[founder effect]] causes rapid speciation through both rapid genetic drift and selection on a small gene pool. | + | The second mechanism of speciation is [[peripatric speciation]], which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the [[founder effect]] causes rapid speciation through both rapid genetic drift and selection on a small gene pool. (Templeton AR, The theory of speciation via the founder principle [http://www.genetics.org/cgi/reprint/94/4/1011] , Genetics) |
The third mechanism of speciation is [[parapatric speciation]]. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.<ref name=Gavrilets/> Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass ''[[Anthoxanthum|Anthoxanthum odoratum]]'', which can undergo parapatric speciation in response to localized metal pollution from mines.<ref>{{cite journal |author=Antonovics J |title=Evolution in closely adjacent plant populations X: long-term persistence of prereproductive isolation at a mine boundary |journal=Heredity |volume=97 |issue=1 |pages=33–37 |year=2006 |pmid=16639420 |url=http://www.nature.com/hdy/journal/v97/n1/full/6800835a.html}}</ref> Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants, causing reproductive isolation. Selection against hybrids between the two populations may cause ''reinforcement'', which is the evolution of traits that promote mating within a species, as well as [[character displacement]], which is when two species become more distinct in appearance.<ref>{{cite journal |author=Nosil P, Crespi B, Gries R, Gries G |title=Natural selection and divergence in mate preference during speciation |journal=Genetica |volume=129 |issue=3 |pages=309–27 |year=2007 |pmid=16900317}}</ref> | The third mechanism of speciation is [[parapatric speciation]]. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.<ref name=Gavrilets/> Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass ''[[Anthoxanthum|Anthoxanthum odoratum]]'', which can undergo parapatric speciation in response to localized metal pollution from mines.<ref>{{cite journal |author=Antonovics J |title=Evolution in closely adjacent plant populations X: long-term persistence of prereproductive isolation at a mine boundary |journal=Heredity |volume=97 |issue=1 |pages=33–37 |year=2006 |pmid=16639420 |url=http://www.nature.com/hdy/journal/v97/n1/full/6800835a.html}}</ref> Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants, causing reproductive isolation. Selection against hybrids between the two populations may cause ''reinforcement'', which is the evolution of traits that promote mating within a species, as well as [[character displacement]], which is when two species become more distinct in appearance.<ref>{{cite journal |author=Nosil P, Crespi B, Gries R, Gries G |title=Natural selection and divergence in mate preference during speciation |journal=Genetica |volume=129 |issue=3 |pages=309–27 |year=2007 |pmid=16900317}}</ref> | ||
Revision as of 23:15, 6 January 2008
Introduction
In biology, evolution is the change in the inherited traits of a population from generation to generation. These traits are the expression of genes that are copied and passed on to offspring during reproduction. Mutations in these genes can produce new or altered traits, resulting in heritable differences (genetic variation) between organisms. New traits can also come from transfer of genes between populations, as in migration, or between species, in horizontal gene transfer. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through natural selection or randomly through genetic drift.
Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits to become rarer. This occurs because organisms with advantageous traits pass on more copies of these traits to the next generation. The measurement of selection on correlated characters (Evolution, volume 37 Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.) [1] In contrast, genetic drift produces random changes in the frequency of traits in a population. Genetic drift arises from the element of chance involved in which individuals survive and reproduce.
One definition of a species is a group of organisms that can reproduce with one another and produce fertile offspring. However, when a species is separated into populations that are prevented from interbreeding, mutations, genetic drift, and the selection of novel traits cause the accumulation of differences over generations and the emergence of new species. Stephen Gould, The Structure of Evolutionary Theory, Belknap Press, ISBN 0-674-00613-5 . The similarities between organisms suggest that all known species are descended from a common ancestor (or ancestral gene pool) through this process of gradual divergence. {Douglas J. Futuyma, Evolution, Sinauer Associates, Sunderland, Massachusetts, ISBN 0-87893-187-2 )
The theory of evolution by natural selection was first proposed by Charles Darwin and Alfred Russel Wallace and set out in detail in Darwin's 1859 book On the Origin of Species[2]. Related earlier ideas were acknowledged in [3] In the 1930s, Darwinian natural selection was combined with Mendelian inheritance to form the modern evolutionary synthesis, "understanding evolution" in which the connection between the units of evolution (genes) and the mechanism of evolution (natural selection) was made. This powerful explanatory and predictive theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth. [4] Statement on the Teaching of Evolution, The Interacademy Panel on International Issues, [5] Statement on the Teaching of Evolution, American Association for the Advancement of Science.
Heredity
Inheritance in organisms occurs through discrete traits – particular characteristics of an organism. In humans, for example, eye color is an inherited characteristic, which individuals can inherit from one of their parents. (Sturm RA, Frudakis TN, Eye colour: portals into pigmentation genes and ancestry). Inherited traits are controlled by genes and the complete set of genes within an organism's genome is called its genotype. Genetics: what is a gene? (Nature, v. 441, 2006)
The complete set of observable traits that make up the structure and behavior of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment.Template:Cite journal (Epigenetics and phenotypic variation in mammals, Mamm. Genome
- Dawkins, R. The Selfish Gene: 30th Anniversary Edition ISBN 0199291152
- Brian Charlesworth, Evolution, ISBN 0-192-80251-8
- Gould, S.J. , Wonderful Life: The Burgess Shale and the Nature of History]], iISBN 0-393-30700-X
- Carroll, S., Endless Forms Most Beautiful, ISBN 0-393-06016-0
- Smith, C.B. and Sullivan, C., The Top 10 Myths about Evolution, ISBN 978-1-59102-479-8
History of evolutionary thought
- Larson, E.J. , Evolution: The Remarkable History of a Scientific Theory, ISBN 0-679-64288-9
- Zimmer, C. , Evolution: The Triumph of an Idea, ISBN 0-060-19906-7
Advanced reading
- Gould, S.J., The Structure of Evolutionary Theory, isbn=0-674-00613-5
- Futuyma, D.J. , Evolution , ISBN 0-878-93187-2
- Mayr, E. , What Evolution Is, ISBN 0-465-04426-3
- Coyne, J.A. and Orr, H.A., Speciation, isbn=0-878-93089-2
- Maynard Smith, J. and Szathmáry, E., The Major Transitions in Evolution, ISBN 0-198-50294-X
- Barton, N.H., Briggs, D.E.G., Eisen, J.A., Goldstein, D.B. and Patel, N.H., Evolution, isbn=0-879-69684-2
