Love is often used by religious apologists. Atheists like myself will point to the burden of proof resting on the religious believer, and they will reply that there's more to life than what can be proved by science such as love, and say things like "...science will never be able to prove that love exists, and it would be silly to ask that of science." The idea being that: science has nothing to say on love, and believing in love is fine, therefore, believing in god is also fine. (We'll ignore the faulty logic today). The thing is, science can say a lot about love (and religious claims for that matter, for example the efficacy of prayer).
Firstly, we have lots of evidence that love exists. We feel it and experience it - so there's something going on in the brain. There is ample evidence of the love between myself and my girlfriend, the love between my family and the love between my friends. Through the actions of those in a relationship, it's obvious to see when you are in a loving, and caring relationship, and also when you are not, by appraising the available evidence.
We can look at the physiology of people in love. Seeing someone you're in love with, or attracted to, can increase your pulse and breath rate. In fact, it can also work the other way around - meeting someone in a situation where your pulse and breath rate have been increased, can increase your attraction to that person in what's called the "misattribution of attraction". You're body is behaving as if it's aroused when you meet a person, and so you think it is that person that has caused the physiological response, not the other aspects of the environment. It's not the only case of acting "as if" you are a certain type of person, and then actually becoming that person.
Science can look at the hormones that are involved in love - for example oxytocin, often called the hormone of love, though it's a little more complicated than that (watch out, it has a darker side too).
Evolution can explain perfectly why love evolved - the love of a parent their child is understandable for the propagation of Homo sapiens, and other species (although parental care is not universal). Do other animals experience parental love for their children? One would presume less so in the sloth, who I've heard (but can't find a reference for online, and all my books are in boxes in a storage unit) leave babies that fall to the forest floor to die, as going to get them puts them at too much risk of predation.
What about the love of a partner? In mammals, for example, testicle size correlates with monogamy, polygamy and harems. Gorilla's testicles are about 0.03% of their bodyweight, and they have harems. A gorilla doesn't need to produce much sperm, as it has control over who it mates with. Chimpanzees on the other hand have testicles that are 0.3%, and they are highly promiscuous - as the female chimps have many partners, a male chimp must produce lots of sperm so as to have higher reproductive success. Humans, interestingly, fall in between these two extremes with 0.08% of bodyweight being testicles.
It may be very difficult to find out if animals feel love, but certainly we can look at how they behave, and the biochemistry that's going on when they do and see how it matches up with what happens in us when we are in love. This is what makes science fantastic: Asking questions and being happy with the answer "I don't know" whilst working on a way to find out.Love is certainly within the realms of science, even if it has to take a different approach.
Now, some people might say that understanding love would spoil it. I will let Richard Feynman explain why I don't agree with that:
"I have a friend who's an artist and he's some times taken a view which I don't agree with very well. He'll hold up a flower and say, "look how beautiful it is," and I'll agree, I think. And he says, "you see, I as an artist can see how beautiful this is, but you as a scientist, oh, take this all apart and it becomes a dull thing." And I think he's kind of nutty.
First of all, the beauty that he sees is available to other people and to me, too, I believe, although I might not be quite as refined aesthetically as he is. But I can appreciate the beauty of a flower.
At the same time, I see much more about the flower that he sees. I could imagine the cells in there, the complicated actions inside which also have a beauty. I mean, it's not just beauty at this dimension of one centimeter: there is also beauty at a smaller dimension, the inner structure...also the processes.
The fact that the colors in the flower are evolved in order to attract insects to pollinate it is interesting -- it means that insects can see the color.
It adds a question -- does this aesthetic sense also exist in the lower forms that are...why is it aesthetic, all kinds of interesting questions which a science knowledge only adds to the excitement and mystery and the awe of a flower.
It only adds. I don't understand how it subtracts."