I see this all the time with bananas that go from green to brown without turning yellow, I always heard people blame the bananas getting too cold during shipping.
I lost it when I moved but we used to have a chart on the fridge that said which fruits you should or should not store together because they make each other ripen faster.
Anyone who has stuffed a banana into a pack or bag knows that bananas also speed up banana ripening. If you're going on an all-day hike, take the almost-ripe banana.