I\'m trying to continue the species mostly because the act of trying to continue the species is very enjoyable. I know this sounds crude, and it is on some level, but it\'s still true. I don\'t need a philosophical reason to enjoy sex.
Fundamentally, the sex drive is extremely powerful. This is probably why most religions try to tame it.
I don\'t want to sound the \"that atheist\" who says religion is worthless. I don\'t employ it, but I know some people who do to great effectiveness. For some reason, I personally don\'t need \"reasons\". I like results. If I can consistently explain traffic by how many crows cross my path in the morning, then I am happy with the Crow-SigAlert Theory.
So things reproduce because it\'s \"fun\" to reproduce. Why is it \"fun\" to reproduce? Well, those who found it fun in the past tended to, well, reproduce. Thus we are all ancestors of things that like to have sex. So we like to have sex.
Asking why the first thing liked to have sex is a tautology. Is there a greater purpose to having sex, like serving some sort of god? I don\'t know. But if that\'s what you\'re thinking about when Angelina Jolie comes bouncing through \"Tomb Raider\", you\'re not going to as likely as I am to create another thing that likes to reproduce.
EDIT: Please don\'t take my near-vulgar tone to imply that I think the point of view expressed by Uloim is invalid. I think he has a very powerful point. I just disagree with his underlying assumption. The world needs diversity, though. If we were all cantankerous mathematicians like me, I would go nuts. My wife and most of my closest friends are artists, not scientists, they\'re more fun to be around.