Intuition suggests that if a trait is under genetic control, then selection for improved performance will increase the frequency of the genetic variant conferring that advantage (as well as co-inherited genetic variants). If selection persists then eventually all of the individuals carrying the unfavorable variant may be culled thus resulting in only the one variant of the mutation in the population and thus logically an exhaustion of genetic variability. Because sustainable genetic gain, or the ability to adapt to a changing environment (in light of changing economic and social policy as well as changes in weather and climate), is predicated on the presence of genetic variability, this expected loss in genetic variation, suggest that the response to selection or ability to adapt genetically will reduce and eventually halt. Although genetic variance is expected to reduce in the initial generations of selection, empirical evidence, in general, does not support the thesis of an eventual exhaustion of genetic variability; arguably the most recognized evidence originates from the Illinois corn lines selected for high and low content of oil in the kernel. The quantity of exploitable genetic variation in a population is dictated by evolutionary forces such as selection, migration, mutation and genetic drift. The extent of variability introduced by mutations is actually high and is thought to represent 0.1% of the environmental variance; this is equivalent to approximately 0.3% for a trait with a coefficient of genetic variability of 10%. Moreover, developments in genomic tools and approaches, both through whole genome selection and genome editing has the potential to reduce the demise of standing genetic variation and even (strategically) introduce genetic variability. For example, genome editing has recently been used to edit the CD163 gene in pigs to increase resistance to the recently isolated arterivirus porcine reproductive and respiratory syndrome (PRRS). Reality, however, does not always reflect potential, and pressures to capture market share may unduly place greater emphasis on short-term genetic gain to the determinant of long-term gain.