Every now and then, we come across one of those feel-good stories about people receiving generous gestures from complete strangers and then paying it forward to another person they don’t know. These stories intrigue us partly because they seem to go against our basic understanding of how human beings behave. If we’re all rational creatures, shouldn’t we act selfishly at all times?

Scientists are equally fascinated. For years, they’ve been trying to learn more about how altruism works. Now a group of American and Chinese researchers have found the perfect opportunity to study pay-it-forward behavior: Observing users on China’s most popular social platform.

Tencent’s WeChat is omnipresent in China and boasts more than a billion monthly active users. One of its most popular features is the ability to send digital red packets, allowing people to send each other gift money over the app up to RMB 200 (US$30). The 21st century take on an age-old East Asian ritual proved immensely popular and helped popularize WeChat Pay.

Digital red packets can even offer more fun than their paper forebearers. Instead of sending just one red packet to each friend, you can also create one giant red packet for sharing among members of a group chat. The system randomly splits the money and assigns varying amounts to the recipients. The results are public as each person opens the red packet, so all group members can see who got what.

You might think this would result in a bunch of group chat free riders, but here’s where things get interesting. Researchers found that the recipients don’t always pocket all their winnings. Instead, they may choose to pay it forward by using some of that money to create another shareable red packet. Among the 3.4 million WeChat users examined, recipients on average paid forward about 10% of the amount they received.

The rate was even higher for the luckiest recipients. Those who received the highest amount in each draw were 1.5 times more likely to pay it forward than other recipients.

Part of this might have to do with social pressure. Researchers found that it’s the norm for the luckiest recipient to send out the first subsequent red packet.

But it also looks like there are more factors at play. It turns out that some group chats completely consist of members who aren’t WeChat friends. Recipients in these groups, less likely to be driven by reputational concerns, still pay forward about 5% of the amount they receive.

Researchers suggest it could be that people simply prefer a more equal distribution, prompting luckier recipients to dispense some of their good fortune.

The researchers also admitted there are limitations to this experiment. It only focuses on one particular cultural group -- Chinese -- using a unique app feature that’s missing on major Western social platforms. And some questions remain. What would happen if the users were anonymous and didn't know how much others received?

The hope is that when we have better answers, they will give us more clues as to how to foster generosity in real life. After all, social experiments encouraging acts of kindness don’t always work.

Earlier this year, a Panera Bread offshoot in Boston shut down after seven years. The non-profit operation gave patrons the option to pay more than the suggested price to support cheaper meals for others who weren't as well-off. The company said they closed the venture because it was “no longer viable.”