Final answer:
Commensalism is a symbiotic relationship where one species benefits while the other species is unaffected. It is not obligatory for the species that does not receive benefits, and coevolution does not occur in commensalisms.
Step-by-step explanation:
Commensalism is a symbiotic relationship between two species in which one species benefits while the other species is unaffected. It is not obligatory for the species that does not receive any benefits. Coevolution does not occur in commensalisms.