Why?

I didn't expect this question phase to be like solving a hundred riddles every day.  I stumble along trying to answer each one correctly until I hit upon the "right" answer.  Why do dogs bark?  Why does the sun shine?  Why do we have hair? Why do cars go?  What happens if there isn't any food?  What happens if I couldn't walk?  I struggle between trying to give Zach a serious answer but also not making it too complicated for him to understand (that's assuming I actually know the complicated answer). You can fill in any of the hundred why/what questions I get and they pretty much go like this:

Zach: Why do we have noses?

Me: So that we can smell things and so we can breath.  (Good answer, right?)

Zach:  But why do we have noses?

Me: (trying my same answer in case it works this time)  So we can smell things and it also helps us to breath.

Zach: What happens if we don't have noses?

Me: Um? We wouldn't be able to smell anything!

Zach: Would we die?

Me: No. We can breath through our mouth too.

Zach: Why do we have noses?

Me: I don't know anymore.

Zach: No mommy, why do we have noses?

Me:  (trying another tactic) Because God made us with noses?!?

Zach: Oh!