This is quite interesting! Thanks for sharing! So might it be that a species, as a whole, benefits from carrying around a certain amount of “spandrels”? A genetic insurance policy of sorts to protect against/quickly adapt to unforeseen changes? Has there been any research into the prevalence (or absence) of spandrels in species that have gone extinct?
I'm not sure if there's much research in evolution about species that have gone extinct versus extant species, or at least I haven't encountered it.
The human genome carries around a massive amount of spandrels, in the form of what is called "selfish DNA." About 15% of the human genome consists of repeats of a single sequence: the Alu gene, which seems to primarily exist to replicate itself in the genome. This is part of a class of genes called transposable elements:
And when discovered in corn, accounted for 85% of the genome. Barbara McClintock, their discoverer, hypothesized that they serve as a growth bed for evolution. And over the years it has indeed been found that individual transposable elements can serve as the seeds for new control sequences that coordinate when to turn genes on and off. The major forces of evolution in vertebrates are not big changes in proteins, but rather changes in when and how various proteins get activated, and transposable elements serve a big function in allowing that sort of evolutionary change in genomic sequences.
Does most repetitive DNA in the genome seem to be useless, in that its deletion or replacement have little effect on the genome? Probably! But all that fluff also facilitates more easy rearrangement of the genome, because if every part of the genome was essential, randomly moving a chunk of DNA into a new spot would likely kill off some useful stuff. But if there's a bunch of stuff that is useless, randomly copying some stuff into a random spot is less likely to disrupt something. If the genome is a hard drive, there's no "free list" or file system for the genome, so random writes are less likely to be disastrous if there's nothing of importance on most of the drive.
I used to get upset at the term "junk DNA" but I don't really care one way or the other now. One cell's junk is another's treasure.
