A change in the gene pool that is brought about completely by chance, and has nothing to do with natural selection, is called a genetic drift.
The frequencies of genotypes in a 15 member peccary population, in a given study area are:-
10 individuals with genotype BB - has a frequency of 0.66
4 individuals with genotype Bb - has a frequency of 0.26
1 individual with genotype bb - has a frequency of 0.06
If the single individual with the genotype bb were struck by lightening, or the individual was killed by a falling cactus, the genotype frequency in this study population would suddenly change from 0.06 bb to 0.00 bb.
This is a genetic drift, a chance event that caused a sudden and relatively large change in the ratios of the genotypes in a small population.
Obviously, such random changes are not influenced by the relative adaptiveness of the peccary's bristle length or of any other gene combination. Thus, genetic drift may be toward longer bristles or toward shorter bristles, toward useful adaptations or away from them regardless of other factors.
It is a random process.