It's Better to Be Recessive than Dominant. Let's suppose you;re a mutation. Congratulations! Whether by cosmic rays, quantum mechanics, or divine intervention, you've come into existence, the hardest part. Now, how about survival? Which would you rather be: neutral junk, recessive beneficial, or dominant beneficial? (We can assume you don't want to to be a fitness-detrcating gene.) (Click here to read more.)

This is the same as junk DNA. It is best to have regressive DNA. That way you can lurk. Being dominant, you'll get wiped out in some era when you're not optimal.

This is related th why having two sexes is useful, perhaps, to keep dispersion of genotypes into a population and thus make it more robust to environmental changes.

But junk DNA and recessives have no defense against mutation. If one of them is mutated, the mutation can survive just as well. A dominant, on the other hand, which is mutated will probably mutate to a harmful form and will immeidately die out, with no chance of taking over by genetic drift.