Couples who give each other intimate kisses several times a day share similar communities of saliva-dwelling oral bacteria. Romantic, right? But don't panic — many of these bacteria are essential for the digestion of food, synthesizing nutrients, and preventing disease.
Some couples are lucky enough to share not only their passions for one another, but their joint passion for scientific exploration. These photos, taken mostly in the first half of the twentieth century, celebrate couples who expanded our knowledge of the world together.