The millennial generation’s breezy approach to sexual intimacy helped give rise to apps like Tinder and made phrases like “hooking up” and “friends with benefits” part of the lexicon.

But when it comes to serious lifelong relationships, new research suggests, millennials proceed with caution.

Helen Fisher, an anthropologist who studies romance and a consultant to the dating site Match.com, has come up with the phrase “fast sex, slow love” to describe the juxtaposition of casual sexual liaisons and long-simmering committed relationships.

Young adults are not only marrying and having children later in life than previous generations, but taking more time to get to know each other before they tie the knot. Indeed, some spend the better part of a decade as friends or romantic partners before marrying, according to new research by eHarmony, another online dating site.