Evidence of Common Descent in Evolution
In a discussion on transitional forms in evolutionary biology, creationist Paul Glenn Cawley declares that there is no evidence that living organisms share common descent:
“Those who adhere to the evolutionary theory act like it’s been proven that all life “descended” from common ancestors when in fact it has NOT been proven! The best biology has proven is that living forms VARY within their own kind.”
This is not true. The following are links to lines of evidence for the common descent of life of which I’m aware:
- All living things share the same structure of genetic code for DNA, RNA and the reading of DNA and RNA to create proteins (read: Cassandra’s Tears; Darwin Was Right). Recently, scientists have created an living, reproducing artificial organism with different nucleotides than used in nature (read: Nick Statt). This indicates that the nucleotides being used aren’t the only possible ones; and yet all living things do share the same basic code, indicating shared origins.
- The similarity of two organisms’ genomes is strongly correlated with the length of time since the point in the fossil record at which the two organisms diverged (read: National Center for Biotechnology Information).
- Organisms that appear to be more related according to other lines of evidence (such as fossil records of transitional forms and phenotypic similarity) also have functional proteins that are more similar to one another (read: Carl Zimmer, Douglas Theobald, Cassandra’s Tears). Organisms that are more distantly related according to the fossil record and phenotype share less similarity in the makeup of the proteins that regulate their biology.
- The more closely related two organisms appear to be according to other lines of evidence, the greater the similarity in their shared set of non-coding genes and endogenized viral code (virus DNA incorporated into a host’s DNA) — two markers of shared history of inheritence that are passed down (read: Cassandra’s Tears, Douglas Theobald, Phylointelligence).
- Chromosome changes– the correlation of chromosome number, type and structure (including the migration of centromeres and chromosome fusion) with other indicators of common descent (read: Discover magazine, Alec MacAndrew, Phylointelligence).
- Vestigial organs are present in distributions that match transitional forms in the fossil record (read: Cassandra’s Tears).
- Non-expressed genes for features shared by ancestors (teeth in birds, gill slits in humans) can be found in organisms’ genomes (read: Cassandra’s Tears, University of Montana).
- Differences within and across classes, orders and families are greater across longer spans of time and longer spans of geographic space (read: Cassandra’s Tears, University of Montana, University of California at Berkeley).
- The discovery of large numbers of transitional forms between different classes, orders and families (read: RationalWiki, TransitionalFossils.com, Smithsonian Institution, Robin Lloyd, University of California at Berkeley, Douglas Theobald).
- The same island species are not spread uniformly across similar islands around the globe; rather, they are limited to islands that are close to one another (read: University of Montana, University of California at Berkeley).
If you’re aware of other web-available resources documenting additional lines of evidence for common descent of Earth’s living organisms, or enriching the lines already listed above, please add a comment and I’ll be glad to update this list. Thanks!