Difference between revisions of "Universal common ancestry"

Revision as of 15:14, September 18, 2007

Jesus likes to sexually abuse small children!

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-'''Universal common ancestry''' is the idea that all life on Earth is related because every species has descended from a [[common ancestor]] or ancestral [[gene pool]].  It is a tenet of the [[Theory of evolution]], and a belief rejected by [[Creationism]].
+Jesus likes to sexually abuse small children!
-== History ==
-Universal common ancestry is an ancient idea.  Many ancient [[pagan]]s held that humans were related to animals.  [[Anaxagoras]], for instance, argued that humans are related to fish, but became humans because the water became too crowded, and the fish kicked humans out of the water.  Many ancient American Indian cultures also believed humans were descended from animals, and some commemorated these beliefs through [[totem pole]]s.<ref>http://www.hud.gov/local/shared/working/r10/nwonap/totems.pdf</ref>
-More recently, in the 18th and 19th centuries, the idea of universal common ancestry regained popularity in [[Europe]].  In 1745, French mathematician and scientist Pierre-Louis Moreau de Maupertuis (1698-1759) wrote in his book ''Venus Physique'':
-:"Could one not say that, in the fortuitous combinations of the productions of nature, as there must be some characterized by a certain relation of fitness which are able to subsist, it is not to be wondered at that this fitness is present in all the species that are currently in existence? Chance, one would say, produced an innumerable multitude of individuals; a small number found themselves constructed in such a manner that the parts of the animal were able to satisfy its needs; in another infinitely greater number, there was neither fitness nor order: all of these latter have perished. Animals lacking a mouth could not live; others lacking reproductive organs could not perpetuate themselves... The species we see today are but the smallest part of what blind destiny has produced..."
-[[Charles Darwin]] further popularized the idea with his book, ''[[Origin of Species]]'', in which he wrote:
-:"[P]robably all of the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed."
-:"The whole history of the world, as at present known, ... will hereafter be recognised as a mere fragment of time, compared with the ages which have elapsed since the first creature, the progenitor of innumerable extinct and living descendants, was created."
-:"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."
-== Bases for belief ==
-=== Similarities ===
-Belief in common descent is largely derived from the similarity among forms of life. For example:
-*All [[cell]]s are bound by a [[membrane]]
-*All cells store heritable information as [[DNA]].
-*All cells adhere to the same basic mechanism of [[gene expression]].
-*All cells utilize the same [[metabolic]] pathways.
-*All cells have [[ribosome]]s to produce [[protein]].
-From these similarities, an evolutionist infers that all life is related through one original life form.
-==== Criticism ====
-Creationists argue that the inference of common ancestry cannot reasonably be drawn from similarity, for two reasons:
-* Similarity is not meaningful evidence of common ancestry
-* Differences which cannot be explained by evolutionary mechanisms are powerful evidence ''against'' common ancestry.
-To illustrate the first objection, one might argue that all ''cars'' are related because they have four tires, an internal combustion engine, a steering wheel, etc.  However, obviously cars are not related; they simply share ''common design characteristics''.  In the same way, creationists argue that just because humans and plants both have cell membranes is no more evidence of ''common ancestry'' than it is of ''common design''.
-The second objection relies on incidents of [[irreducible complexity]] and [[specified complexity]] to point to the unlikelihood that all life forms diversified through variation and selection alone.  They point to issues such as:
-* The transition from non-self-reproducing chemicals to self-replicating cells: the process of self-replication requires an enormous number of components be present in the cell for it to function at all, and none of the components required for self-replication serve any purpose unless all are present simultaneously; therefore it is unreasonable to conclude that [[abiogenesis]] occured without [[design]].
-* The transition from asexual reproduction to sexual reproduction: male reproductive organs are incredibly complex, and serve no purpose unless female reproductive organs (which are equally, if not more, complex) already exist.  Therefore the sexes could not have evolved in a step-wise fashion, because neither set of reproductive organs would serve any purpose unless the other set already existed.
-For the above reasons, creationists conclude that similarity does not provide meaningful evidence of common ancestry.
-=== Shared endogenous retroviruses ===
-A [[Retrovirus]] is a virus that incorporates itself into an host cell's DNA, and programs the host cell to produce copies of the cell.  [[Endogenous retrovirus]]es (ERVs) are retroviruses that infected an organism's [[germ cell]]s, and were thus passed to the next generation, and incorporated into the organism's genetic line over time.
-Researchers estimate that 1% of the human genome is occupied by ERVs, constituting approximately 30,000 different ERVs.<ref>Sverdlov, E. D. (2000) "Retroviruses and primate evolution." BioEssays 22: 161-171. [http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=10655035&dopt=AbstractPlus]</ref>  Some of these ERVs are shared by humans and apes, and are found in the same place in the respective genomes.  <ref>Lebedev, Y. B., Belonovitch, O. S., Zybrova, N. V, Khil, P. P., Kurdyukov, S. G., Vinogradova, T. V., Hunsmann, G., and Sverdlov, E. D. (2000) "Differences in HERV-K LTR insertions in orthologous loci of humans and great apes." Gene 247: 265-277.[http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=10773466&dopt=AbstractPlus]</ref>
-From these facts, evolutionists argue that these ERVs are shared by humans and primates because they were inherited by a common ancestor.
-==== Criticism ====
-Evolutionists gloss over two important facts when making this argument: First, many retroviruses can infect both humans and apes.  The most notable of these is [[HIV]], which is widely believed to have originated as [[SIV]] in chimpanzees, but can also infect humans, apes, and monkeys.<ref>http://news.bbc.co.uk/1/hi/health/5012268.stm</ref>  It is entirely possible, therefore, that humans and apes were ''independently infected'' with the same virus.  Second, some retroviruses have been shown to have highly targetted insertion points, meaning that the virus selects very specific segments of the genome for insertion.<ref>Citation: (2004) Retroviral Gene Vectors Show Clear Target Preferences. PLoS Biol 2(12): e443 doi:10.1371/journal.pbio.0020443 [http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020443&ct=1]</ref>  Consequently, it is entirely possible that the same virus infected both humans and apes, and targetted the same location.  This seems especially plausible in light of the fact that humans and apes have ''tens of thousands'' of endogenous retroviruses in their respective genomes -- at least a ''few'' of the retroviruses are likely to infect both humans and apes at the same location.
-Additionally, scientists have determined that some endogenous retroviruses are indispensible to a species' life or reproduction.<ref>"Researchers Discover that Sheep Need Retroviruses for Reproduction," Texas A&M AgNews, 11 Sep 06.[http://agnews.tamu.edu/dailynews/stories/ANSC/Sep1106b.htm]</ref>  If the retrovirus is advantageous in some way, that would explain how the retrovirus spread to the entire species.  It also presents the possibility that retroviruses were used as part of the creative process, as [[retrovirus]]es are often used in genetic engineering today, to introduce new genetic material to cells.
-=== Common DNA-based genes in diverse species ===
-The most persuasive argument for common ancestry is existence of common DNA-based genes in diverse species. But there are at least three other plausible explanations -- [[parallel evolution]], [[horizontal gene transfer]], and [[creationism]].
-* '''Parallel evolution''':  Some people who believe in evolution deny universal common ancestry.  They point out that there is still no good theory for how DNA-based life could have arisen from non-life. If it happened once, it may have happened many times. Some people say that separate evolution might have had an entirely different genetic code, but no one knows. It may well be that DNA-based life evolved from non-life many times, and the descendants of that life are living today.
-* '''Horizonal gene transfer''': It is also known that genes sometime migrate somehow from one species to another species, so having a common gene is not proof of common ancestry.  Maybe there is no universal common ancestor, and important genes were spread by horizontal gene transfer.
-* '''Creationism''': Creationists argue that common genes in diverse species is no more evidence of ''common descent'' as it is of ''common design''.
-== References ==
-<References/>
-[[Category:Evolution]]
-[[Category:Creationism]]

Difference between revisions of "Universal common ancestry"

Revision as of 15:14, September 18, 2007

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