When George Valliant followed 268 Harvard undergraduate men for their entire adult lives as part of the famous Grant Study, he generated a whole lot of data and a host of interesting findings. But his bottom line conclusion was pretty simple:

"The 75 years and $20 million expended on the Grant Study points...to a straightforward, five-word conclusion: 'Happiness is love. Full stop.'"

Which is a pretty solid reason to pay a lot of attention to the art and science of a long and happy romantic partnership. But this is a professional website, so if you need a more practical reason, here's one from a recent study--a stable relationship with a solid partner is a huge boost for your career, as well.

But you probably knew all this intuitively already. What most non-scientists don't know--but would like to find out--is the latest research-backed advice on how to maintain such a fruitful partnership. Helen Fisher knows. A biological anthropologist, she holds academic positions at The Kinsey Institute and Rutgers University, but she's also the chief scientific adviser for Match.com. Recently, she spoke to Big Think about what science has to say about making sure your relationship--and your happy feelings for one another--last.

1. Wait a while to marry.

Hookup culture has its share of critics, but Fisher isn't one of them. "Maybe all of this hooking up and friends with benefits and living together is not recklessness. Maybe it's caution. Maybe singles are trying to learn every single thing they can about a potential partner before they tie the knot," she says.

This slowly, slowly approach to commitment is probably a good thing, as we're really not at our most rational at the beginning of a relationship. In that early, intense phase, "some cognitive regions up in the prefrontal cortex that have evolved much more recently begin to shut down," explains Fisher. Primitive areas associated with craving and obsession, however, light up like a Christmas tree.

So take it slow before you commit, recommends Fisher. "I think that with what I call fast sex, slow love, with this slow love process of getting to know somebody very carefully over a long period of time, it's going to help the brain readjust some of these brain regions for decision making," she says. "I'd wait at least two years, because in two years you see the full cycle of the year twice. You see how they handle Halloween, how they handle Christmas or Hanukkah, how they handle summer fun." Plus, by then the primitive part of your brain will have started to calm down a bit, giving rationality a chance to weigh in.

2. Have sex.

This one probably isn't such a shocker, but insane schedules and stress can, of course, get in the way of doing what comes naturally. Don't let them, advises Fisher.

"Have sex regularly with the partner. If you don't have time, schedule the time to have sex with the partner, because when you have sex with a partner, you're driving up the testosterone system, so you're going to want to have more sex. But you also have all the cuddling, which is going to drive up the oxytocin system and give you feelings of attachment, and...any kind of stimulation of the genitals drives up the dopamine system and can sustain feelings of romantic love," she says, explaining the "use it or lose it" principle of the human sex drive.

3. Do new stuff together.

Can long-term relationships lose some of their spark? Of course, but you can fight boredom and complacency by stirring more novelty into your lives together. "Novelty drives up the dopamine system and can sustain feelings of romantic love," explains Fisher. "Just go to a different restaurant on Friday night. Take your bicycle instead of a car. Read to each other in bed. Sit together on the couch and have a discussion about something new. Read new books together. Novelty, novelty, novelty sustains feelings of intense romantic love."

4. Stay in touch.

No, she's not referring to all-day text messages or frequent phone calls while you're traveling for work. She means it literally--touch each other. "Cuddle after dinner. Walk arm in arm down the street. Hold hands together. Put your foot on top of his or her foot while you're having dinner, gently of course. But stay in touch. That drives up the oxytocin system and can give you feelings of deep attachment to the partner," says Fisher.

5. Say nice things, daily.

Like regular sex, when you write this one down, it seems pretty obvious. But in the fog of everyday life, it can be easy to forget this simple bit of relationship wisdom. "If you say several nice things to your partner every day--I would suggest five but if you can only pull off two or three, whatever, saying nice things to your partner--that actually reduces their cholesterol, reduces their cortisol, which is the stress hormone, and boosts their immune system. But it also boosts yours," Fisher reports of the research on the subject.

If you're intrigued by the tidbits here, the complete video has a lot more detail on the science behind these ideas. You can check it out here.