First, I will be focusing on introns found in protein-coding genes. In other words, these are the introns that interrupt sequence that code for amino acids and are removed by spliceosomes in order to form the mature mRNA. There are other introns that may have front-loaded the existence of these protein-coding introns, but that is another topic for another day. For now, when I refer to ‘introns,’ I am referring to introns found in protein-coding genes
Second, I am going to use the following hypothesis as a guide: introns facilitated the evolution of metazoan life.
This hypothesis stems from two teleological vantage points:
1. Since the early 2000s, I have proposed a modest front-loading hypothesis where unicellular life was designed to frontload the appearance of metazoan life. Since that time, this hypothesis has become increasingly more plausible with the discovery of all sorts of “metazoan-specific” genes in protozoan life forms (a common topic on this blog). Since we can safely assume that introns were present in these ancient unicellular life forms, we might also suspect that they too helped to frontload the appearance and subsequent evolution of metozoans.
2. The Design Matrix proposes the criterion of Rationality as one means of investigating origins. In this case, introns, upon superficial glance, appear to be irrational and would nudge the DM score toward the non-teleological spectrum. From the perspective of translation, they are just long stretches of meaningless gibberish inserted into coding text and thus need to be cut out. They are not essential to life itself, as bacteria do quite well without any such introns. Yet if introns facilitate the evolution of more complex, metazoan life, the rational essence of the system begins to come into focus. We might even wonder if something as complex as the human brain could emerge without them.
Third, I am not proposing or defending the notion that each and every intron has a function that serves the cell. Instead of this reductionist approach, we’ll consider introns from the larger perspective, as a class, as a whole. In other words, most introns can indeed be examples of “junk,” but the question is whether such junk can be used to carry out an objective over time. We can explore individual cases of introns, but for them to be ultimately meaningful, they would need to represent an opportunity that would not be too narrowly restricted for use throughout all of evolution.
In the next entry, I will lay out a fundamental clue that supports this front-loading hypothesis.