Is it scientifically verified that bananas will ripen faster when kept in a bowl with other fruit? I've heard you shouldn't keep bananas in a bowl with other fruit. But they all look so happy together.

What I'd like to see is hard science here. Or at least documented and repeatable observation. For example, I read lots of people saying simply "it's the ethylene gas", but what's eluded my searching eye is a chart of which common fruits emit how much of this gas, or the ripening effect of x amount of this gas for y duration at z distance from other fruits in the vicinity. I'd do an experiment myself, but I don't have any particular biology expertise to properly structure a control, etc., and maybe it's already been done?

While I'm not saying this oft-heard claim is false, I am saying I've neither been convinced that it's verifiably so as far as having been proven, nor convinced that any ripening-hastening is of significant concern (shortens the life of a banana by a day or more). If it is, we'll have to issue a cease-and-desist order to my household regarding the convenient stacking of all our colorful fruit friends in one place.

Follow-up inquiry: Even if this banana ripening-rate-quickening is true for apples and oranges, are there certain fruits that are okay to leave in the bowl with bananas?
I think you've got this mostly backwards. The reason not to store bananas with other fruit is that the ripening bananas emit a lot of ethylene gas and will cause the other fruit to spoil more quickly. You can also use this to your advantage: got a pear that you want to ripen quicker? Put it in a paper bag with ripe bananas overnight. 

Other fruit emits ethylene as well, but generally in large quantities only when they are already quite ripe.

Here is a pretty good reference: http://www.csmonitor.com/2006/0531/p15s01-lifo.html