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If two species are descended from a common ancestor, then fossils of a common ancestor, with traits common to both species, might exist.

If two species are descended from a common ancestor, then fossils of a common ancestor, with traits common to both species, might exist.

In fact, '''tens of thousands''' of fossils have been found with traits corresponding to predicted common ancestors of modern species.  Furthermore, additional thousands of fossils have been found cataloguing the divergence and gradual adaptation of ancestral forms into modern species<ref>Godfrey (1984).  ''Scientists confront creationism''.</ref><ref>http://www.nature.com/nature/journal/v440/n7085/abs/nature04639.html</ref><ref>http://www.nature.com/nature/journal/v450/n7172/abs/nature06277.html</ref><ref>Seriously, just google "ancestral fossil" or "transitional fossil" if you can't wrap your head around this one.</ref>. Commonly cited examples of both ancestral and "transitional" fossils are found in the evolutionary history of whales.

In fact, '''tens of thousands''' of fossils have been found with traits corresponding to predicted common ancestors of modern species.  Furthermore, additional thousands of fossils have been found cataloguing the divergence and gradual adaptation of ancestral forms into modern species.<ref>Godfrey (1984).  ''Scientists confront creationism''.</ref><ref>http://www.nature.com/nature/journal/v440/n7085/abs/nature04639.html</ref><ref>http://www.nature.com/nature/journal/v450/n7172/abs/nature06277.html</ref><ref>Seriously, just google "ancestral fossil" or "transitional fossil" if you can't wrap your head around this one.</ref>  Commonly cited examples of both ancestral and "transitional" fossils are found in the evolutionary history of whales.

Whales are estimated to have diverged from the lineage leading to modern ungulates around 55-60 million years ago<ref>http://www.pnas.org/content/95/26/15464.short</ref>. Fossils of an animal, called ''Pakicetus'', with unambiguous ancestral whale-like traits are found in strata dated to ~50-53 million years ago.  Pakicetus was a land-dwelling carnivore, somewhat similar in size and appearance to a modern wolf (more illustratively, imagine a carnivorous dog-sized goat).

Whales are estimated to have diverged from the lineage leading to modern ungulates around 55-60 million years ago.<ref>http://www.pnas.org/content/95/26/15464.short</ref>  Fossils of an animal, called ''Pakicetus'', with unambiguous ancestral whale-like traits are found in strata dated to ~50-53 million years ago.  Pakicetus was a land-dwelling carnivore, somewhat similar in size and appearance to a modern wolf (more illustratively, imagine a carnivorous dog-sized goat).

Moving into younger strata, the fossil record provides a detailed stepwise transition from ''Pakicetus'', to ''Ambulocetus'' (a family of animals very similar to ''Pakicetus'', but more adapted to a semi-aquatic lifestyle), to ''Remingtonocetus'' (clearly well-adapted to a mostly aquatic lifestyle), to ''Protocetus'' (the earliest whale fossils found outside of the area around western India), to the ancestral divergence of modern whale families.

Moving into younger strata, the fossil record provides a detailed stepwise transition from ''Pakicetus'', to ''Ambulocetus'' (a family of animals very similar to ''Pakicetus'', but more adapted to a semi-aquatic lifestyle), to ''Remingtonocetus'' (clearly well-adapted to a mostly aquatic lifestyle), to ''Protocetus'' (the earliest whale fossils found outside of the area around western India), to the ancestral divergence of modern whale families.

These fossils also show the stepwise emergence of complex traits, most notably the cetacean-specific inner-ear adaptations required for acute underwater hearing and echolocation <ref>http://www.nature.com/nature/journal/v361/n6411/abs/361444a0.html</ref><ref>http://www.ncbi.nlm.nih.gov/pubmed/3692104</ref>.

These fossils also show the stepwise emergence of complex traits, most notably the cetacean-specific inner-ear adaptations required for acute underwater hearing and echolocation.<ref>http://www.nature.com/nature/journal/v361/n6411/abs/361444a0.html</ref><ref>http://www.ncbi.nlm.nih.gov/pubmed/3692104</ref>

Many other evolutionary transitions have been documented in the fossil record, but even more compelling evidence for common ancestry is found in the field of genetics.

Many other evolutionary transitions have been documented in the fossil record, but even more compelling evidence for common ancestry is found in the field of genetics.

==Genetics==

==Genetics==

Beyond providing a set of "blueprints", an organism's genome provides a sort of history book on the organism's descent and ancestry.  The theory of evolution would predict that species with a more recent common ancestor should have more similar genomes than species with more distant common ancestors.  Further, common descent would predict that all species should have some highly conserved genetic similarities.  Once again, both of these predictions have been found to be correct<ref>http://www.ncbi.nlm.nih.gov/pubmed/19140982</ref>.

Beyond providing a set of "blueprints", an organism's genome provides a sort of history book on the organism's descent and ancestry.  The theory of evolution would predict that species with a more recent common ancestor should have more similar genomes than species with more distant common ancestors.  Further, common descent would predict that all species should have some highly conserved genetic similarities.  Once again, both of these predictions have been found to be correct.<ref>http://www.ncbi.nlm.nih.gov/pubmed/19140982</ref>

Variation in physical traits (phenotype) is driven by variations in genes (genotype).  When a random genetic variation occurs, it is called a "mutation".  The vast majority of mutations have absolutely no effect on phenotype whatsoever, those mutations that do affect phenotype provide are the "raw materials" of the evolutionary process.

Variation in physical traits (phenotype) is driven by variations in genes (genotype).  When a random genetic variation occurs, it is called a "mutation".  The vast majority of mutations have absolutely no effect on phenotype whatsoever, those mutations that do affect phenotype provide are the "raw materials" of the evolutionary process.

Mutations that impair an organism's ability to survive and reproduce in its environment are selected against and usually do not persist in a population for more than a few generations.  Mutations that improve an organism's ability to survive and reproduce in its environment become more prevalent within a population over generations, as individuals carrying the mutation will tend to have more offspring than individuals without it.

Mutations that impair an organism's ability to survive and reproduce in its environment are selected against and usually do not persist in a population for more than a few generations.  Mutations that improve an organism's ability to survive and reproduce in its environment become more prevalent within a population over generations, as individuals carrying the mutation will tend to have more offspring than individuals without it.

That more closely related species are more genetically similar to one another has been established for a few decades.  An entire discipline of biology, [[comparative genomics]], is devoted to studying the differences in genomic structure and function between species (or, sometimes, populations of the same species), in order to better understand the mechanisms of evolution and the mechanisms of gene regulation<ref>http://www.sciencemag.org/content/287/5461/2204.short</ref><ref>http://www.sciencemag.org/content/286/5439/458.short</ref><ref>http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627966/</ref>.

That more closely related species are more genetically similar to one another has been established for a few decades.  An entire discipline of biology, [[comparative genomics]], is devoted to studying the differences in genomic structure and function between species (or, sometimes, populations of the same species), in order to better understand the mechanisms of evolution and the mechanisms of gene regulation.<ref>http://www.sciencemag.org/content/287/5461/2204.short</ref><ref>http://www.sciencemag.org/content/286/5439/458.short</ref><ref>http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627966/</ref>

One surprising finding to come out of the earliest studies in comparative genomics was just how genetically similar most species are.  This finding led to a major paradigm shift (spawning, in its wake, the field of [[evo-devo]]), and, after much research, revealed for the first time the major molecular (that is, genetic) mechanisms of evolution<ref>Gilbert (2006).  ''Developmental biology''.</ref>.

One surprising finding to come out of the earliest studies in comparative genomics was just how genetically similar most species are.  This finding led to a major paradigm shift (spawning, in its wake, the field of [[evo-devo]]), and, after much research, revealed for the first time the major molecular (that is, genetic) mechanisms of evolution.<ref>Gilbert (2006).  ''Developmental biology''.</ref>

Some of the most highly conserved genes (that is, genes with the least variation between species) are the genes encoding for ribosomal RNAs (rRNA).  Comparing rRNA sequences allows investigators to infer the evolutionary relationships between distantly related species.  For example, rRNA studies have been used to estimate the relationships between the eukaryotic taxa (e.g. plants, animals, and fungi)<ref>http://www.mol-palaeo-lit.de/pdf/baldauf/2008/10278_Baldauf2008.pdf</ref><ref>http://rspb.royalsocietypublishing.org/content/266/1415/163.short</ref><ref>http://www.sciencemag.org/content/239/4841/748.short</ref>, and even delve into the complex relationship between the three major domains of life (bacteria, archea, eukarya)<ref>http://www.pnas.org/content/107/29/12739.short</ref><ref>http://mmbr.asm.org/content/73/4/565.short</ref>.

Some of the most highly conserved genes (that is, genes with the least variation between species) are the genes encoding for ribosomal RNAs (rRNA).  Comparing rRNA sequences allows investigators to infer the evolutionary relationships between distantly related species.  For example, rRNA studies have been used to estimate the relationships between the eukaryotic taxa (e.g. plants, animals, and fungi),<ref>http://www.mol-palaeo-lit.de/pdf/baldauf/2008/10278_Baldauf2008.pdf</ref><ref>http://rspb.royalsocietypublishing.org/content/266/1415/163.short</ref><ref>http://www.sciencemag.org/content/239/4841/748.short</ref> and even delve into the complex relationship between the three major domains of life (bacteria, archea, eukarya).<ref>http://www.pnas.org/content/107/29/12739.short</ref><ref>http://mmbr.asm.org/content/73/4/565.short</ref>

Transposable DNA elements (noncoding sequences which are, almost always, nonessential) can also be used to determine the relationship between more closely-related species<ref>http://www.retrovirology.com/content/6/S2/P54/abstract</ref><ref>http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0014745</ref><ref>http://mbe.oxfordjournals.org/content/25/9/1795.short</ref>. In fact, this technique of using transposable elements to determine phylogeny uses the same principles as the [[DNA fingerprinting]] techniques used in human paternity tests.  That separate species would share some non-coding and nonessential DNA sequences strongly implies shared ancestry.

Transposable DNA elements (noncoding sequences which are, almost always, nonessential) can also be used to determine the relationship between more closely-related species.<ref>http://www.retrovirology.com/content/6/S2/P54/abstract</ref><ref>http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0014745</ref><ref>http://mbe.oxfordjournals.org/content/25/9/1795.short</ref>  In fact, this technique of using transposable elements to determine phylogeny uses the same principles as the [[DNA fingerprinting]] techniques used in human paternity tests.  That separate species would share some non-coding and nonessential DNA sequences strongly implies shared ancestry.

==Conclusion==

==Conclusion==

There is, in fact, a very large body of evidence supporting the theory of evolution.  It is because of this large body of evidence that acceptance of the theory of evolution is virtually unanimous among biologists<ref>http://www.scienceeducationreview.com/open_access/wiles-evolution.pdf</ref>.

There is, in fact, a very large body of evidence supporting the theory of evolution.  It is because of this large body of evidence that acceptance of the theory of evolution is virtually unanimous among biologists.<ref>http://www.scienceeducationreview.com/open_access/wiles-evolution.pdf</ref>

==References==

==References==