There are many classic examples of evidence that support evolution, such as endogenous retroviruses or transitional fossils, but I would like to focus on another piece of evidence that I think is just as powerful and hopefully just as easily understood. That evidence deals with exons and introns.
As a bit of a refresher . . .
In eukaryotes, a classical gene is made up of exons and introns. The exons are the sections of the gene that make their way into the messenger RNA. That mRNA is used as a template for making proteins. Introns are sections of DNA that are transcribed into RNA but are cut out of the primary RNA to make the mRNA. The mnemonic device I was taught is that the exons are the cities and the _intr_ons are the _inter_state highways between the cities.
As such, introns are mostly made up of functionless DNA. Short microRNA genes can be found in a relative few introns, and the sequences around the splice sites do have function as part of mRNA maturation. However, the vast majority of intron sequence lacks function. Obviously, the vast majority of exons have function. So you have the cities of functional sequence (exons) and interstates of largely non-functional sequence (introns).
With these facts in mind, what does creationism predict with respect to a comparison of exons and introns between species?
As far as I can tell, creationism would predict that introns should be nearly identical between species, even very different species like humans and chickens. We are told that God would copy things instead of starting over with new sequence, and virtually the same intron sequence would work equally well in chickens as they would in humans. However, if you want a different looking species then you need different function in those shared genes. Therefore, the exons should be different between species. Therefore, we should see more differences between exons than between introns when we compare the same gene between species. This is the prediction made by the “Common Designer” hypothesis in a situation where species or “kinds” are created independently and don’t share common ancestry with other species/kinds. If a creationist disagrees, I would like to here why with a solid explanation to back it, one that is also consistent with their assertion that shared features are due to Common Design.
In subsequent posts I will discuss what the theory of evolution predicts, and why.