So.why do anything. Why shave, lift weights, get an education, wear nice clothes....you'll just be dead one day anyway.
Bingo! A philosophy that accepts death as a "'natural" thing is doomed to go in circles, all the questions it raises are empty, so are the answers. I'm talking about a "limited" time here as an "unavoidable".
That's why human races biggest challenge now aren't wars of diff. religions, poverty or other shit like that (chances are - they won't affect you and me too much). Tho' there's one thing that will affect us ALL, it's an evolutionary "fail" (an uncomplete work, due to accidental circumstances) that makes us detorriate after a certain age (it simply just happened this way for our specie, as there ARE species with an UNDEFINED life-span, as they doesn't age. Evolution took care of that too..), we call it "aging".
Bearing kids, as Uberman writes, IS a strategy of survival, but not for you or me, it's a strategy of survival for a SPECIE, so it could achieve that MAIN goal of lowering chances of death as much as possible, further, to a point where "reproducing" will become a trivial thing, as the "vessel" (that's a product of a genome, and a carrier of it too) will be advanced enough to sustain it's life as it is (by not dieing of a mollecular havoc, called - aging). It will take a LONG time to achieve that (if at all) in this "old school" way tho'.
The technology based biological evolution is what must (and will) happen, that's when people will cease to be so egoistical, that's when they'll really start to care about the enviroment (as they'll know - they aren't here for a very short space of time, but for - maybe quite long one.. unless bus will hit them on the street) about each other and generally - keeping peace in this fucked up place.
This probably sounds very outrageous to some, but it will happen, just like everything that happened already (people living 3x longer than just a few centuries ago.. Doesn't seem that many opposes that now, eh..).
I've got carried away, and english not being my first language, I may not sound eloquent enought, but I guess you get the point. So to answer your question... I honestly don't know "why", find a reason for yourself, whatever it would be, and don't believe in anyone who says they "know the real one", as chances are - that's just their reasoning of the same futile philosophy I mentioned before (and a fear of death. Don't mistake fear of death and a fear of a detorriation. I'm personally not afraid of dieing, thus I don't have any reason to believe in anything called "god". I DON"T GIVE A SHIT if there's one, as non existence is a bliss. A slow suffering on the other hand - is not.).
