Answer:
Reduce genetic diversity
Explanation:
Genetic diversity is an extremely important factor when it comes to evolution. The more diversity and variation there is within a population, the more chances a species has of surviving.
In the case of inbreeding, organisms that are related are selected to mate. This has extremely negative effects on the species such as bad health and infertility issues. In addition, because they all share the same alleles, it results in a decrease in genetic diversity, augmenting the chances of the species to disappear.
This occurs because if, for example, there is an organism that possesses a capability to resist extreme weather conditions and another that does not have this trait, there are still chances to survive, whereas if they are all the same and none of them possess this capability, the probability of this species to go extinct is higher.