Have you ever noticed that it's not uncommon to see co-stars from your favorite series or movie dating in real life? Rachel McAdams and Ryan Gosling, for instance, dated on and off for three years off screen after starring together in "The Notebook." Or maybe you remember that Jennifer Garner and Ben Affleck started dating the year after the release of "Daredevil" back in 2003. Why does this seem to be a pattern?

"Mere exposure to someone repeatedly increases the likelihood we will be attracted to them," J. Celeste Walley-Jean, dean of the School of Graduate Studies and associate professor of psychology at Clayton State University, told INSIDER.

This is backed up by 50 years worth of scientific research that has found that proximity is one of the most powerful indicators of attraction. We simply are drawn to the people we see frequently, which explains why celebrity co-stars end up getting together due to how closely they work with one another on a regular basis.

Whether we realize it or not, we are biologically attracted to people who look healthy.

"Heterosexual men are typically attracted to younger women who appear to be of childbearing age and physical appearance," Walley-Jean told INSIDER. This can explain why women in the 1800s wearing bustles to overemphasize their healthy, childbearing hips in order to attract men.

Additionly, research suggests that people are also attracted to those who look healthy. Face symmetry, face structure, and hip-shoulder ratios are all important when it comes to attraction because these physical features indicate good health, according to Live Science.

Our environment teaches us who we should view as attractive.

Beyond physical features, Walley-Jean said our families, peers, and media all play a role in helping us learn what to view as attractive. For instance, some heterosexual people may seek out partners who share attributes that remind them of their opposite-sex parent.