The theoretical arguments about lethal mutation frequencies that are used as arguments for neutral theory (that is why proponents of neutral theory cannot seem to abandon the term "junk DNA"), severely restricts how much functional DNA there can be within the context of random mutation theory. This means that the idea that natural selection produced complexity in the true, constructive sense were actually abandoned by mainstream science the moment neutral theory was adopted. The limiting factors model is actually a completely different theory altogether, based on denying possible mechanisms of evolution instead of considering possibilities. It assumes sheer sabotage of possibilities, unlike classic neo-Darwinism which proposed a mechanism for evolution which was the best alternative known in its time. Sabotagial neo-neo-Darwinists, on the other hand, just refuse to accept new possiblilities discovered since. See also inheritance of acquired characteristics.
The ENCODE project have shown that at least 80% of the human genome is functionally active. Sabotagial neo-neo-Darwinists try explaining it away by claiming that most of the activity is insignificant, but that away-explanation ignores several factors. One is that reading DNA is a job done by energy-expensive reading molecules, making any major amount of meaningless DNA activity extremely unlikely. The role of energy-consuming histons in DNA replication also makes retention of large amounts of insignificant DNA unlikely, especially in cells that divide fast and often. Another factor is the missing heredity: protein-coding genes can only explain a minor fraction of the heredity shown by twin studies. Sabotagial neo-neo-Darwinists explain away discoveries of functions in non-coding DNA by claiming that they are a minority case and that the vast majority is still junk, theoretically "supporting" it by reference to limitations of how many mutations natural selection can purge per generation. But they are overlooking the fact that hereditary diseases that cannot be explained by protein-coding DNA outnumbers those that can 20 to 1 (and since the factor 20 figure is from 2011 and hereditary diseases are rapidly being discovered, the factor must now be much greater than 20). That is patently not the "minor border revision" the sabotagial neo-neo-Darwinists are talking about. Rather, it is a massive expansion of the amount of functionally important genome that makes directed mutations necessary to avoid that literally everybody dies from genetic diseases.
This quantitatively massive amount of "lethal" mutations means that we all literally need at least dozens if not hundreds or even thousands of "miraculous" self-corrections that reductionist medicine considers impossible, just to stay alive, indeed, it is absolutely necessary for even making the risk of extremely early miscarriage (at the embryonic stage) any lower than 100%, see Possible mechanisms: Retroviruses in inheritance of acquired characteristics. Since such supposedly impossible self-corrections are mathematically proven to be necessary for our existence, it is time to stop denying their existence. Of course believing that it is impossible creates a very dangerous, destructive version of the placebo effect known as the nocebo effect. It is often claimed that stressing the importance of thinking should "blame ill people for not improving themselves", but that claim is absurdly naively taking the concept of blaming for granted. As shown in brain, tolerant environments creates extreme recoveries after brain damage that established neurological and psychological theories cannot explain. So the solution is to eradicate blaming so thoroughly that nobody feels any need to make up or use justifications on the lines of "I cannot help it". See Advice of ways to stop justifying and Moderating the free will debate. Another example of environmental conditions shaping the ability of living beings to correct their own genes is the fact that wasps with their well-protected eggs, larvae and pupps that do not have to be wary of predation (and therefore have more peace and calm to self-correct) can live with only one set of chromosomes, without the back-up genes of double sets of chromosomes, as shown by the fact that wasp males comes from unfertilized eggs. This also means that all eugenics is silly, not only the coercive form but also voluntary "not passing on genetic diseases" thinking.
See also origin of HIV.