What primary reason explains why populations might experience inbreeding?

Populations often experience inbreeding primarily due to small population size. In smaller populations, the number of potential mates is limited, which increases the likelihood that individuals will breed with close relatives. This can lead to a higher chance of offspring inheriting identical alleles from both parents, resulting in a reduced genetic diversity within the population.

Inbreeding can have various consequences, such as an increase in the expression of deleterious recessive traits, which can affect the overall health and viability of the population. Genetic drift also plays a significant role in small populations, further compounding the effects of inbreeding by disproportionately influencing allele frequencies over generations.

While other factors such as lack of diverse environmental conditions, natural barriers to migration, and high mutation rates can influence a population's genetics or dynamics, they do not directly initiate inbreeding as a consequence of population structure in the same way that a small population size does.