I'm going to put my controversial hat on for a minute.
I don't think love is a single emotion. Its a whole bundle of them rolled up in one. It's happiness, protectiveness, fear (of losing the other person), jealousy, wanting to care for someone, empathy, sadness (when your partner is sad), and a whole bundle more.
I think men are less capable of love than women are. Not at a genetic level or anything, but because we're taught from birth that we're not allowed to display our emotions, or at least the ones that make us "weak". So we take that on board, and as we can't show those emotions we hide them down and eventually we feel them less.
Men aren't allowed most of those emotions, we've forgotten how to feel them. Protectiveness, jealousy, we're allowed them. And most men will protect their partners when they feel they're under threat, and will get jealous if they think their partners are looking elsewhere.
But empathy, being caring, nope, we've lost those skills. We're allowed to do happy, as long as it's not happy. And we kind of get fear and sadness, but mostly they come out as a kind of anger.
Which finally and belatedly leads me to the point of the thread. What makes you pull your weight in a relationship? What makes you get up off your arse to go load the dishwasher, when you've had a really shit day? Its love. Its the thought that if you don't do it, your partner will have to, and they've probably had just as much of a shit day as you have.
And on the flipside, what makes women stay in relationships with lazy partners, with crappy partners? Again it's love. Its an overwhelming all encompassing emotion that blinds them to the fact that the person they love is taking them for a ride.
Love - women feel to much of it, and men don't feel it enough.