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When people hear the word "evolution," they most commonly think of divergent evolution<ref> http://bioweb.cs.earlham.edu/9-12/evolution/HTML/converge.html</ref>, the evolutionary pattern in which two species gradually become increasingly different. Divergent evolution occurs when a group from a specific population develops into a new species. In order to adapt to various environmental conditions, the two groups develop into distinct species due to differences in the demands driven by the environmental circumstances. On a large scale, divergent evolution could responsible for the creation of the current diversity of life on earth from the first living cells. On a smaller scale, it could responsible for the evolution of humans and apes from a common primate ancestor. On a molecular scale, it could be responsible for the evolution of new catalytic functions of enzymes and membrane protein topology. <ref>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&list_uids=11395407&dopt=Abstract</ref> <ref> http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=17552</ref>

When people hear the word "evolution," they most commonly think of divergent evolution<ref> http://bioweb.cs.earlham.edu/9-12/evolution/HTML/converge.html</ref>, the evolutionary pattern in which two species gradually become increasingly different. Divergent evolution occurs when a group from a specific population develops into a new species. In order to adapt to various environmental conditions, the two groups develop into distinct species due to differences in the demands driven by the environmental circumstances. On a large scale, divergent evolution could responsible for the creation of the current diversity of life on earth from the first living cells. On a smaller scale, it could responsible for the evolution of humans and apes from a common primate ancestor. On a molecular scale, it could be responsible for the evolution of new catalytic functions of enzymes and membrane protein topology. <ref>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&list_uids=11395407&dopt=Abstract</ref> <ref> http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=17552</ref>

==Divergent Evolution and Speciation==

===Divergent Evolution and Speciation===

If different selective pressures are placed on a particular organism, a wide variety of adaptive traits may result. If only one structure on the organism is considered, these changes can either add to the original function of the structure, or they can change it completely. Divergent evolution leads to speciation, or the development of a new species. Divergence can occur when looking at any group of related organisms. The differences are produced from the different selective pressures. Any genus of plants or animals can show divergent evolution. An example can involve the diversity of floral types in the orchids. The greater the number of differences present, the greater the divergence. Scientists speculate the greater that two similar species diverge indicates a longer length of time that the divergence originally took place.

If different selective pressures are placed on a particular organism, a wide variety of adaptive traits may result. If only one structure on the organism is considered, these changes can either add to the original function of the structure, or they can change it completely. Divergent evolution leads to speciation, or the development of a new species. Divergence can occur when looking at any group of related organisms. The differences are produced from the different selective pressures. Any genus of plants or animals can show divergent evolution. An example can involve the diversity of floral types in the orchids. The greater the number of differences present, the greater the divergence. Scientists speculate the greater that two similar species diverge indicates a longer length of time that the divergence originally took place.

==Examples of Divergent Evolution==

===Examples of Divergent Evolution===

There are many examples<ref>http://www.sciencemag.org/cgi/content/abstract/290/5491/516</ref> <ref>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11308083&dopt=Abstract</ref> of divergent evolution in nature. If a freely-interbreeding population on an island is separated by a barrier, such as the presence of a new river, then over time, the organisms may start to diverge. If the opposite ends of the island have different pressures acting upon it, this may result in divergent evolution. Or, if a certain group of birds in a population of other bird of the same species varies from their migratory track due to abnormal wind fluctuations, they may end up in new environment. If the food source is such that only birds of the population with a variant beak are able to feed, then this trait will evolve by virtue of its selective survival advantage. The same species in the original geographical location and having the original food source do not require this beak trait and will, therefore, evolve differently.

There are many examples<ref>http://www.sciencemag.org/cgi/content/abstract/290/5491/516</ref> <ref>http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11308083&dopt=Abstract</ref> of divergent evolution in nature. If a freely-interbreeding population on an island is separated by a barrier, such as the presence of a new river, then over time, the organisms may start to diverge. If the opposite ends of the island have different pressures acting upon it, this may result in divergent evolution. Or, if a certain group of birds in a population of other bird of the same species varies from their migratory track due to abnormal wind fluctuations, they may end up in new environment. If the food source is such that only birds of the population with a variant beak are able to feed, then this trait will evolve by virtue of its selective survival advantage. The same species in the original geographical location and having the original food source do not require this beak trait and will, therefore, evolve differently.

Convergent evolution<ref> http://www.pbs.org/wgbh/evolution/library/01/4/l_014_01.html</ref> causes difficulties in fields of study such as comparative anatomy. Convergent evolution takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure. Environmental circumstances that require similar developmental or structural alterations for the purposes of adaptation can lead to convergent evolution even though the species differ in descent. These adaptation similarities that arise as a result of the same selective pressures can be misleading to scientists studying the natural evolution of a species.  Convergent evolution also creates problems for paleontologists using evolutionary patterns in taxonomy, or the categorization and classification of various organisms based on relatedness. It often leads to incorrect relationships and false evolutionary predictions.

Convergent evolution<ref> http://www.pbs.org/wgbh/evolution/library/01/4/l_014_01.html</ref> causes difficulties in fields of study such as comparative anatomy. Convergent evolution takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure. Environmental circumstances that require similar developmental or structural alterations for the purposes of adaptation can lead to convergent evolution even though the species differ in descent. These adaptation similarities that arise as a result of the same selective pressures can be misleading to scientists studying the natural evolution of a species.  Convergent evolution also creates problems for paleontologists using evolutionary patterns in taxonomy, or the categorization and classification of various organisms based on relatedness. It often leads to incorrect relationships and false evolutionary predictions.

==Examples of Convergent Evolution==

===Examples of Convergent Evolution===

One of the best examples<ref> http://cas.bellarmine.edu/tietjen/Evolution/convergent_evolution_examples.htm</ref> of convergent evolution involves how birds, bats, and pterosaurs (all different species that evolved along distinct lineages at different times) learned to fly. Importantly, each species developed wings independently. These species did not evolve in order to prepare for future circumstances, but rather the development of flight was induced by selective pressure imposed by similar environmental conditions, even though they were at different points in time. The development potential of any species is not limitless, primarily due to inherent constraints in genetic capabilities. Only changes that are useful in terms of adaptation are preserved. Yet, changes in environmental conditions can lead toward less useful functional structures, such as the appendages that might have existed before wings. Another change in environmental conditions might result in alterations of the appendage to make it more useful, given the new conditions.

One of the best examples<ref> http://cas.bellarmine.edu/tietjen/Evolution/convergent_evolution_examples.htm</ref> of convergent evolution involves how birds, bats, and pterosaurs (all different species that evolved along distinct lineages at different times) learned to fly. Importantly, each species developed wings independently. These species did not evolve in order to prepare for future circumstances, but rather the development of flight was induced by selective pressure imposed by similar environmental conditions, even though they were at different points in time. The development potential of any species is not limitless, primarily due to inherent constraints in genetic capabilities. Only changes that are useful in terms of adaptation are preserved. Yet, changes in environmental conditions can lead toward less useful functional structures, such as the appendages that might have existed before wings. Another change in environmental conditions might result in alterations of the appendage to make it more useful, given the new conditions.

Parallel evolution<ref> http://www.britannica.com/search?miid=1215119&query=parallel+evolution</ref> occurs when unrelated organisms develop the same characteristics or adaptive mechanisms due to the nature of their environmental conditions. Or stated differently, parallel evolution occurs when similar environments produce similar adaptations. The morphologies (or structural form) of two or more lineages evolve together in a similar manner in parallel evolution, rather than diverging or converging at a particular point in time.

Parallel evolution<ref> http://www.britannica.com/search?miid=1215119&query=parallel+evolution</ref> occurs when unrelated organisms develop the same characteristics or adaptive mechanisms due to the nature of their environmental conditions. Or stated differently, parallel evolution occurs when similar environments produce similar adaptations. The morphologies (or structural form) of two or more lineages evolve together in a similar manner in parallel evolution, rather than diverging or converging at a particular point in time.

==Examples of Parallel Evolution==

===Examples of Parallel Evolution===

One example is the complex plumage patterns that seem to have evolved independently among many very different bird species.<ref> http://www.sciencemag.org/cgi/content/summary/303/5665/1779</ref>

One example is the complex plumage patterns that seem to have evolved independently among many very different bird species.<ref> http://www.sciencemag.org/cgi/content/summary/303/5665/1779</ref>

Investigating the biomechanics of the auditory system reveals that only one of these subgroups has a tympanum. The other subgroup has developed a different mouthear structure that does not have a typanum, but has a mouthear with functional characteristics essentially the same as the subgroup with the tympanum. The evolutionary significance of how hearing capabilities developed in parallel in two different subgroups of a species reveals that distinct mechanisms can exist leading to similar functional capabilities with differing means for acquiring the same functional attribute. For both subgroups, hearing must have been an important characteristic for the species to survive given the environmental conditions.

Investigating the biomechanics of the auditory system reveals that only one of these subgroups has a tympanum. The other subgroup has developed a different mouthear structure that does not have a typanum, but has a mouthear with functional characteristics essentially the same as the subgroup with the tympanum. The evolutionary significance of how hearing capabilities developed in parallel in two different subgroups of a species reveals that distinct mechanisms can exist leading to similar functional capabilities with differing means for acquiring the same functional attribute. For both subgroups, hearing must have been an important characteristic for the species to survive given the environmental conditions.

==Parallel Evolution and Speciation==

===Parallel Evolution and Speciation===

Parallel speciation is a type of parallel evolution in which reproductive incompatibility in closely related populations is determined by traits that independently evolve due to adaptation to differing environments. These distinct populations are reproductively incompatible and only populations that live in similar environmental conditions are less likely to become reproductively isolated. In this way, parallel speciation suggests that there is good evidence for natural selective pressures leading to speciation, especially since reproductive incompatibility between to related populations is correlated with differing environmental conditions rather than geographical or genetic distances.

Parallel speciation is a type of parallel evolution in which reproductive incompatibility in closely related populations is determined by traits that independently evolve due to adaptation to differing environments. These distinct populations are reproductively incompatible and only populations that live in similar environmental conditions are less likely to become reproductively isolated. In this way, parallel speciation suggests that there is good evidence for natural selective pressures leading to speciation, especially since reproductive incompatibility between to related populations is correlated with differing environmental conditions rather than geographical or genetic distances.