Good question, but it needs to be separated from all the other common definitions as there are different answers for each of them. I assume you mean love for your partner, rather than love for an idea or material belonging. In which case, are you talking about the initial lust phase or the love that you feel after that.
I have an answer for both, and it goes down the reductionist rationalist path as you might have guessed.
And while we are on the subject can you let us have your answer
On a tangential question, could I also have your thoughts on Darwinian evolutionary theory and whether you 100% believe in it for now?
I don't think we need to seperate out love for a person from love for an idea, both can be felt just as passionately.
My answer? I'm not sure and I'd be lying if I told you anything else, though I suspect love is more than just a feeling - perhaps, and I do not stand by this completely, but love could be the very reason for being.
Evolution is an accepted scientific theory and I accept it as much as I accept any other scientific construct - it makes sense and it is useful in constructing further theories and concepts to make our human vantage point seem more useful. However, science isn't in the business of making true statements, it's in the business of making of falsifiable statements. Evolution is a useful theory, just like gravity, but it isn't the truth no matter how close it gets.
And to get back to love, it is the only principle upon which a utopia can be built, it is the greatest feeling man has ever experienced, it is the meaningful part of our existence. I don't know how or why love is, but I know that what it is must be more than a reduction to materialist ontology.
And yes, sorry therationaliser for not being clear, q-man is correct - I did mean materialist reductionism in a metaphysical sense.