A Scientific Investigation builds on this work in that it assumes animal origins of laughter and follows van Hooff's distinction between the laugh and the smile. The two expressions are often mentioned in the same breath because they tend to grade into each other, yet they derive from quite different primate displays, with the smile expressing affection and appeasement rather than playfulness. Robert R. Provine has set himself the task of cracking the laugh code, as he calls it, rather than tackling the much more complex issue of humor. The two may appear inseparable, but one of the revelations of this book is that the stand-up comedy model of laughter as a response to jokes is mistaken. The large majority of laughs measured by Provine and his students in the shopping malls and on the sidewalks of the human natural habitat occurred after statements that were far from humorous.
Laughter is a loud display that much of the time seems to signal mutual liking and well-being.
Some of its uses are unique to our species, such as the guffaws of bonding. When a group of people laugh, sometimes at the expense of outsiders, they broadcast solidarity and togetherness not unlike a howling pack of wolves. Provine expands on this theme with the observation that women laugh more in response to men's remarks than the reverse. The asymmetry between the sexes starts early in life, between boys and girls, and seems to be cross-cultural. The man as laugh-getter also turned up in an analysis of personal ads, in which Provine found that women generally sought partners with a sense of humor, which male advertisers claimed to have in great measure.