Changes

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>https://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>https://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>https://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>