Pleas from a YEC

[Mystical]

Yeah I can see how my green eyes mutation from a blue eyed mother would just be the end of humanity as we know it.

Bacteria mutate much faster than plants and animals do, yet their populations are not becoming less viable.

Most mutations are neutral. Nachman and Crowell estimate around 3 deleterious mutations out of 175 per generation in humans (2000). Of those that have significant effect, most are harmful, but the fraction which are beneficial is higher than usually though. An experiment with E. coli found that about 1 in 150 newly arising mutations and 1 in 10 functional mutations are beneficial (Perfeito et al. 2007).

The harmful mutations do not survive long, and the beneficial mutations survive much longer, so when you consider only surviving mutations, most are beneficial.

Whether a mutation is beneficial or not depends on environment. A mutation that helps the organism in one circumstance could harm it in another. When the environment changes, variations that once were counteradaptive suddenly become favored. Since environments are constantly changing, variation helps populations survive, even if some of those variations do not do as well as others. When beneficial mutations occur in a changed environment, they generally sweep through the population rapidly (Elena et al. 1996).