Final answer:
Self-fertilization can reduce the fitness of offspring by limiting genetic diversity, which can lead to a higher probability of inheriting harmful genetic traits and reduced adaptability.
Step-by-step explanation:
A possible negative consequence of an organism engaging in self-fertilization is reducing the fitness of offspring. This reduction in fitness can arise due to a lack of genetic diversity, as self-fertilization means the offspring are essentially clones with very little genetic variability. This can lead to an increased chance of offspring inheriting harmful genetic traits, reducing their chances of survival and reproduction in a changing environment. In contrast, sexual reproduction introduces new genetic combinations, which can increase the adaptability of a population.