We’ve grown up with the idea that dirt is bad. If you drop food on the floor, don’t dare to pick it up and eat it. Sanitize your kitchen and bathroom with “germ killers.” Filter your water. Purify...
What makes us exchange saliva, sebum, bits of food and millions of bacteria with each other? In other words, why do we kiss? This is not an innate activity. South Pacific islanders, for example,...
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