Is there anything as swoony as a long kiss? The simple act of pressing your lips to someone else’s can fuel everything from lust to love. But what does science say about your smooch session? Turns out there’s an entire field—philematology—devoted to the study of kissing. Over the years, researchers have devoted plenty of brainpower to figuring out what happens when human lips meet. Here are a few highlights from the existing body of research on why and how we French, snog, neck, smooch, and just plain pucker up: Maybe we started kissing ‘cause we were hungryIn the earliest days of kissing research, scientists looked to monkeys in the hopes they could unlock truths about human liplocking—and soon, they learned that our species may have started making out because stomachs were rumbling. As early as 1915, researchers observed what looked like kissing in adult chimps. But they were often actually “kiss-feeding,” a friendly but not-so-romantic way of getting pre-chewed food into one another’s mouths. That led to one of the most prevalent theories as to why humans kiss—that the behavior evolved from our ancestors’ gross way of passing the potatoes.