Does an avocado seed help guacamole stay green? My friend was telling me about a habit in the Spanish culture (I'm not sure if it's done elsewhere as well) of leaving the avocado seed inside when making guacamole. The claim is that if you leave the seed inside the guacamole, something in the seed prevents the guacamole from browning.

I'm a little skeptical - I thought that the browning was due to oxidization. If that's the case, then I don't see how a seed could help in preventing oxidization. Am I missing something? Is this true, or just a myth?
You're correct - it's a myth, as is adding something acidic to it like lemon juice--see explanation here. As you said, what causes it to brown is the oxidation, and that's just exposure to the air. If you wrap a cut avocado (or guacamole) in plastic wrap so there's no air space between the wrap and the avocado, then it will stay green longer than areas where air is getting to it.