Final answer:
Loss of variability due to genetic drift can be restored by immigration of new individuals or mutations introducing new alleles into the gene pool.
Step-by-step explanation:
Loss of variability due to genetic drift can be restored by various mechanisms, one of which is the immigration of new individuals into a population, which introduces new alleles. Another method is through mutations, which can create new alleles within a population.
Events like genetic drift can lead to the bottleneck effect, where a disaster causes a significant loss of genetic variability, or the founder effect, where a new population starts with a limited genetic pool. Both effects drastically alter the genetic structure of a population, highlighting the importance of diverse genetic contributions for the resilience of populations.