Moving in together is a big step, but it may not be enough to feel truly committed.

Couples who live together but aren't married don't feel the same levels of security as couples who are legally married.

Researchers studied the effect of holding hands with a partner among couples who lived together, married and not, as well as same-sex couples who aren't legally allowed to marry. They were asked to lie in a scanner while watching a computer screen that signaled a potential threat of a shock to the ankle. During that time, the person was either holding their partner's hand, a stranger's hand, or alone. When married couples held hands, the person threatened with the shock was calmer than when alone or with a stranger.

The same effect didn't occur with opposite-sex couples who were just cohabiting. However, it did with same-sex couples who weren't married but considered themselves married.

Researchers think that it's not the legal or religious recognition of marriage that makes people feel secure; it's more about think thinking of your relationship as being committed to the fullest extent possible.