Is exchange natural?

First of all, X is natural, therefore X is good is fallacious. So it's inadmissible as evidence as far as I'm concerned. I mean if you want to convince me of the value of something you have to do more than just show me that it's natural.
If you look back into the archives I previously talked used the term market where I meant interaction. This was a mistake. Markets are about exchange. There are lots of types of markets but that's the only necessary quality, I think. However, interaction does not necessitate exchange.
The thing that I'm thinking about right now, and doesn't blesh with the market anarchist argument is that this ignores the potentials of a gift economy.
Gifting does not involve any exchange. So how does that fit into The Market?

Anyways how would we decide whether or not something is natural?
Maybe because it has always existed in lots of different environments?
Is slavery natural?
Is war natural?
Is religion natural?
Is government (I use this term with some reservation) natural?

I am using that same fallacy in reverse, by which because X is undesirable, X cannot be natural, but I guess my point is that this is all pointless. I don't see how you can really show that something is Natural.
Well the only thing that I can think of is language.
But is that natural or socially constructed?

Karl Polanyi's The Great Transformation is already on my reading list.

Previously:
Abandoned attempt to figure out exchange and markets and stuff
Market anarchism and communism

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Clarification: I'm not saying whether or not exchange is natural or not, just that it can't really be proven based on observations of human behaviour..