Mung, to petrushka, elsewhere:
Everyone does not understand “genetic load” and those that do claim to understand are probably wrong. Why don’t you start an OP on genetic load and the genetic load argument? That would be interesting. Betting you won’t.
This is such an OP. I believe the genetic load argument*** was initially proposed by Susumu Ohno in 1972, whose paper also introduced the then-scare-quoted term “junk”. It’s brief, accessible, and worth a read for anyone who wishes to offer an opinion/understand (not necessarily in that order).
The short version: sequence-related function must be subject to deleterious mutations. Long genomes (such as those of most eukaryotes) contain too many bases for the entire genome to be considered functional in that way, given known mutation rates. The bulk of such genomes must either have functions that are not related to sequence, or no function at all.
Interestingly, the paper is hosted on the site of an anti-junk-er, Andras Pellionisz, a self-promoting double-PhD’d … er … maverick. Also of interest is that, contrary to some ID narratives, the idea was initially resisted by ‘Darwinists’, if that term is understood not as people who simply accept evolution, but as people who place most emphasis on Natural Selection. Perfectionism is not the sole preserve of Creationists.
More recent work has characterised the nonfunctional fraction, and this lends considerable empirical support to Ohno’s contentions.
[eta: link to comment]
***[eta: in relation to genome size, not the first time anyone, ever, discussed genetic load!]