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'''Common descent''' is a [[scientific theory]] in [[Biology]] it can be applied on two levels, with a [[clad]] or group of species being said to share a recent common ancestor, or the broader theory which states that all organisms on earth originated from common ancestors. The theory is usually used in support of the [[Theory of Evolution]].

'''Common descent''' is an idea in [[Biology]] which is applied on two levels, with a [[clad]] (group of species) being said to share a recent common ancestor, or the broader conjecture which asserts that all organisms on earth originated from common ancestors. The idea of common descent is usually associated with Darwin's [[Theory of Evolution]].

Darwin wrote:

Darwin wrote:

:"When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the [[Silurian]] system was deposited, they seem to me to become ennobled."

:"When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the [[Silurian]] system was deposited, they seem to me to become ennobled."

==Evidence for common descent==

==Arguments for common descent==

There are several lines of converging evidence for common descent. These include but are not limited to:

There are several converging lines of argmuentation for common descent. These include but are not limited to:

*[[Homology | Anatomical homologies]]- The phenotype of organisms often share similar structure. This structure often doesn't serve a specific design function and is most easily explained by constraints of common descent.  

*[[Homology | Anatomical homologies]]- The phenotype of organisms often share similar structure. This structure often doesn't serve a specific design function and is explained by constraints of common descent.  

*[[Endogenous retrovirus | Endogenous retroviral insertions]] - These are inactivated viral genes that were inserted by ancient [[retrovirus]]es. Having the same retrovirus inserted in the same location between two species is best explained by common descent.  

*[[Endogenous retrovirus | Endogenous retroviral insertions]] - These are inactivated viral genes believed to have been inserted by ancient [[retrovirus]]es. Having the same retrovirus inserted in the same location between two species can be explained by common descent.  

*[[Pseudogene]]s - These are genes that no longer code for a protein due to a mutation. Species often share the same pseudogene, with the same inactivating mutation. A famous example of this is the [[L-gulonolactone oxidase]] which synthesizes vitamin c, all simians including humans share this pseudogene but the guinea pig which also has an inactivated L-gulonolactone oxidase gene has a different mutation. This is best explained by common descent.  

*[[Pseudogene]]s - These are genes that no longer code for a protein due to a [[mutation]]. Species often share the same pseudogene, with the same inactivating mutation. A famous example of this is the [[L-gulonolactone oxidase]] which synthesizes vitamin c; humans and all simians share this pseudogene, but the guinea pig which also has an inactivated L-gulonolactone oxidase gene has a different mutation.  

*The convergence of [[phylogenetic tree]]s using anatomical homology, DNA homology, pseudogenes, endogenous retroviral insertions, and many other methods all converge on a similar looking tree. There are slight differences but the general relationships of the tree are intact. If all of these methods were flawed you would not expect each of them to converge on the same tree.  

*The convergence of [[phylogenetic tree]]s using anatomical homology, DNA homology, pseudogenes, endogenous retroviral insertions, and many other methods all converge on a similar looking tree. There are slight differences but the general relationships of the tree are intact. If all of these methods were flawed you would not expect each of them to converge on the same tree.  

*[[Embryology]] -  The [[pharyngula]] stage of embryonic development appears to be highly conserved over time. At this stage it is difficult to tell the difference between various vertebrate species.  

*[[Embryology]] -  The [[pharyngula]] stage of embryonic development appears to be highly conserved over time. At this stage it is difficult to tell the difference between various vertebrate species.  

==Controversy over common descent==

==Objections to common descent==

   

   

Dr. Jonathon Wells published a book in 2002 entitled ''[[Icons of Evolution]]''.  Dr. Wells contends the book shows that "the best-known “evidences” for Darwin’s theory have been exaggerated, distorted or even faked."<ref>http://www.discovery.org/scripts/viewDB/index.php?command=view&id=1180</ref><ref>http://www.iconsofevolution.com/</ref><ref>http://www.discovery.org/articleFiles/PDFs/survivalOfTheFakest.pdf</ref>

Dr. Jonathon Wells published a book in 2002 entitled ''[[Icons of Evolution]]''.  Dr. Wells says that "the best-known “evidences” for Darwin’s theory have been exaggerated, distorted or even faked."<ref>http://www.discovery.org/scripts/viewDB/index.php?command=view&id=1180</ref><ref>http://www.iconsofevolution.com/</ref><ref>http://www.discovery.org/articleFiles/PDFs/survivalOfTheFakest.pdf</ref>

Also, [[Jonathan Wells]] in his book [[Icons of Evolution]] made the claim that many current biology textbooks use distorted pictures of vertebrate embryos to convince students that vertebrates share a common ancestor. [http://www.nmsr.org/jonwells.htm (Wells)] However, this statement has been heavily criticized by many scientists who have reviewed his book as being misleading in some cases and false in others. [http://www.talkorigins.org/faqs/wells/haeckel.html] [http://chem.tufts.edu/AnswersInScience/Coyne-IconsReview.htm]

Also, he says that many current biology textbooks use distorted pictures of vertebrate embryos to convince students that vertebrates share a common ancestor. [http://www.nmsr.org/jonwells.htm (Wells)]

[[category: Evolution]]

On the other hand, noted evolutionist [[Stephen Gould]] wrote the following regarding Ernst Haeckel's work in a March 2000 issue of ''Natural History'':

On the other hand, noted evolutionist [[Stephen Gould]] wrote the following regarding Ernst Haeckel's work in a March 2000 issue of ''Natural History'':