Why Do Bananas in the Same Bunch Ripen at Different Speeds?

I bought a bunch of bananas that were all green, but a few turned yellow days before the rest. They were kept together on the counter, away from direct sunlight. Is the difference down to how mature each banana was when harvested, or can position in the bunch affect ripening too?

I’d also like to know whether separating the bananas actually slows the rest from ripening, or if that’s mostly a kitchen myth.