Parents who tell children to shake hands to make nice or smooth over a conflict are on to something. Shaking hands increases cooperation between people in various negotiations, according to University of California at Berkeley’s Juliana Schroeder, a graduate of Chicago Booth’s PhD program; Chicago Booth’s Jane L. Risen; and Harvard’s Francesca Gino and Michael I. Norton.

However, handshaking might also make you more cooperative than you want to be.

The researchers studied how spontaneous handshaking affects multi-issue, integrative negotiations using two scenarios: the hypothetical sale of a car and a hypothetical job offer. Various outcomes held different weights for the two parties, meaning that negotiators could “grow the pie” with both parties increasing their individual final scores. Participant pairs who spontaneously shook hands at the outset scored significantly higher, whether the pairs were friends or strangers, the researchers find.

Does shaking hands cause people to negotiate more effectively? To test that, the researchers assigned some pairs of participants to shake hands, and instructed others to not shake hands. The negotiators were either told it was customary to shake hands before beginning or were seated without the opportunity to do so.

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Participant pairs who shook hands had higher negotiation scores, according to the study. When their recorded behavior was rated by observers, who didn’t know whether or not the negotiators had shaken hands, the handshakers were observed as being more open discussing their preferences, making more concessions, lying less, and talking and shaking hands after the deal, all socially oriented behaviors.

Being assigned to shake hands boosted cooperation in a prisoner’s dilemma game as well, even for participants not instructed to shake. In one condition of this experiment, only one participant in the pair was instructed to shake hands. Those who received a proffered hand behaved as cooperatively as those instructed to shake, demonstrating that the handshake, and not the instruction, was critical.

At the heart of handshaking’s effects appears to be a signal of cooperation, which was enhanced for integrative negotiations where working together benefited both parties, but also for a single-issue, distributive negotiation where cooperation tended to hurt, rather than help one of the two parties, an individual carrying out a hypothetical sales transaction.

“Buyers who shook hands with the sellers were less likely to lie—even to their own detriment—which made the outcomes more equitable and allowed sellers to do better,” the researchers write. They conclude that the “simple ritual of shaking hands can be a powerful gesture to promote cooperation.”

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