In any finite population, the process of evolution is well known to be influenced by population size and mutation effects [
16].
Beneficial mutations are more frequently fixed in large populations than in small ones, whereas deleterious mutations are more frequently eliminated. Two studies, one based on a theoretical mathematical model [
17], and one on experiments of digital organisms [
18], arrived at a similar conclusion; namely, that
mutational robustness tended to decline with increasing population size, and thus selection in small populations would favor robustness mechanisms. In a population of a given size, the process of evolution will depend on the relative rate of appearance of deleterious and beneficial mutations as well as their actual mutational effects. Selection associated with deleterious mutations will favor lower mutation rates, while beneficial mutations will favor higher mutation rates [
9]. Nevertheless, the evolution of extremely high mutation rates is unlikely to occur unless organisms are under special circumstances [
19] for the reason that beneficial mutations rarely compensate for deleterious mutations. The importance of this interplay between mutation rate and its effects was pointed out by Keightley [
20], who showed that the genome-wide mutation rate and the distribution of fitness effects of mutations could not be simultaneously estimated because they are confounded with one another: a high mutation rate can usually be explained by a low variance in fitness effects, or a low mutation rate with a high variance in fitness effects. Unfortunately, this conclusion is true only for deleterious mutations and further investigation is needed for cases where beneficial mutations also occur.
