How did smooshing our faces together come to signify love and affection?

As we've written about previously, one of the most compelling explanations hinges on the practice of mouth-feeding – the passing of pre-chewed or regurgitated food from the mouth of one animal to another. Lots of species, including humans, are known to mouth-feed. But when and why did we make the leap from mouth-to-mouth feeding to full-blown makeout sessions?

In the latest episode of VSauce, Michael Stevens runs us through a slew of fascinating studies with ties to philematology (the science and study of kissing). Some damn interesting research in this roundup – including several investigations that would have a hard time passing today's institutional review boards.

[VSauce]