Final answer:
Unrelated female helpers in a paper wasp nest gain indirect benefits, such as an increase in the reproductive output of the reproducing female.
Step-by-step explanation:
The most likely explanation for unrelated female helpers in a paper wasp nest is that they gain indirect benefits, such as an increase in the reproductive output of the reproducing female. This behavior can be explained by kin selection, where the worker bees are closely related to the reproducing female and indirectly pass on their genes through her offspring. By helping to rear her offspring, the helpers increase their inclusive fitness.