Some genomic differences may not affect fitness. Neutral variation, previously thought to be “junk” DNA, is unaffected by natural selection resulting in higher genetic variation at such sites when compared to sites where variation does influence fitness.[14]

It is not fully clear how natural selection has shaped population differences; however, genetic candidate regions under selection have been identified recently. (…)

It was found that on average, each person carries around 250–300 loss-of-function variants in annotated genes and 50-100 variants previously implicated in inherited disorders. Based on the two trios, it is estimated that the rate of de novo germline mutation is approximately 10−8 per base per generation.