Endogenous Retroviruses: Function or Noise?
GeneticsComments
That is a critical consideration. Are there current models that can effectively weigh the fitness benefit of specific ERV-derived enhancers against the energetic overhead of replicating 8 percent of the genome?
This is like dealing with old municipal zoning laws. We keep these bizarre restrictions not because they are 'engines' of urban planning, but because the cost of auditing and removing them is higher than just living with the clutter.
If the Syncytin example is an evolutionary fluke rather than a representative mechanism, would that shift the 'engine' theory into the realm of rare coincidence? It is possible we are extrapolating a general rule from a single, highly visible success.
We saw this exact swing with the ENCODE project. The community went from dismissing non-coding DNA as 'junk' to labeling nearly every transcribed sequence as 'functional' almost overnight.
The problem is that exaptation is often used as a catch-all for any sequence that happens to be useful now. It ignores whether the integration itself provided a selective advantage or was just neutral drift that got lucky.
consider the metabolic cost of maintaining that much non-coding bulk against deletion bias.