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LIFE isn鈥檛 easy as a Maasai herder on the Serengeti plain in eastern Africa. At any moment, disease could sweep through your livestock, the source of almost all your wealth. Drought could parch your pastures, or bandits could steal the herd. No matter how careful you are, or how hard you work, fate could leave you destitute. What鈥檚 a herder to do?

The answer is simple: ask for help. Thanks to a Maasai tradition known as osotua 鈥� literally, umbilical cord 鈥� anyone in need can request aid from their network of friends. Anyone who鈥檚 asked is obliged to help, often by giving livestock, as long as it doesn鈥檛 jeopardise their own survival. No one expects a recipient to repay the gift, and no one keeps track of how often a person asks or gives.

Osotua runs counter to the way we usually view cooperation, which is all about reciprocity 鈥� you scratch my back, I鈥檒l scratch yours. Yet similar forms of generosity turn out to be common in cultures around the world. Some anthropologists think it could represent one of the earliest forms of generosity in human society.

That鈥檚 not the only curiosity about generosity. In biological and evolutionary terms, it makes no sense to give and get nothing in return. Altruism is rare in other animals, yet humans can be inexplicably kind. Are we generous by nature? How did we get to be this way? What role does culture play in kindness? These are the big questions now being addressed by researchers in the , who are using fieldwork, experiments and modelling to explore osotua and other examples of human cooperation. Their aim: to find how best to make the milk of human kindness flow.

A friend in need

Osotua isn鈥檛 a responsibility the Maasai take lightly. 鈥淚t is the connecting fibre in society,鈥� says anthropologist Dennis ole Sonkoi at Rutgers University in New Jersey, who is Maasai. Each individual maintains their own network of osotua partners. Once formed, the relationships can last for generations, with parents passing osotua partners on to their children. And it鈥檚 not just the Maasai. 鈥淚n every society we鈥檙e studying, we have found need-based transfers,鈥� says Human Generosity Project co-director Athena Aktipis at Arizona State University in Tempe. Fijians, Tanzanian slum dwellers and American cattle ranchers all pitch in to help neighbours in need, with no expectation of being paid back. Even the Ik of Uganda, whom one anthropologist once vilified as the least generous people in the world, do it.

But the giving is often one-sided. 鈥淪ince I was a kid, there were families that I knew to have a lot of cows. Those families would be the ones that are always approached,鈥� says Sonkoi. On the face of it, they seem to lose much and gain little by participating. Why do they continue to be generous, against their apparent best interests?

A clue lies in the trigger for such generosity: an unpredictable crisis. This suggests that these practices persist because they help manage risk, which pays off for everyone in the long run. Even the best-prepared family can fall prey to catastrophe, such as a sudden illness. These types of risk cannot be prevented, so need-based giving may have emerged as a proto-insurance policy. Prosperous members of many societies share so that this social insurance will be available if they need it 鈥� just as wealthy homeowners insure their belongings against fire. 鈥淵ou鈥檙e exchanging the possibility of a catastrophic loss for the certainty of a small, controllable loss,鈥� says Lee Cronk at Rutgers University, who heads up the Human Generosity Project with Aktipis.

Thinking of osotua-style generosity as insurance could explain why participants don鈥檛 keep a tally of who owes whom. 鈥淚f you don鈥檛 help partners they may not survive, and then they may not be around to help you,鈥� says Aktipis.

To investigate this idea, Aktipis and her colleagues made a computer simulation of a Maasai herding society. Each virtual household had a herd of cattle, which would grow through reproduction but occasionally be hit by a disaster. If numbers fell below 64 cattle 鈥� about what it takes to support a Maasai family 鈥� the household would die.

Aktipis鈥檚 team ran the simulation under three scenarios: one with no giving, one in which potential donors would only give if the asker had paid back previous gifts, and one resembling osotua. show that households survived much longer, on average, with osotua-style giving, supporting the idea that even habitual donors benefit in the long run from keeping their neighbours going.

鈥淲hy do people continue to be generous, against their apparent best interests?鈥�

However, need-based giving works best when risks are 鈥渁synchronous鈥� 鈥� when hardship is likely to strike one family and spare their neighbours. Herding tribes in northern Mongolia, for example, use such generosity to help families crippled by illness. However, the system breaks down when they face their biggest threat, a zud 鈥� a winter storm that prevents livestock from feeding. With everyone affected, helping one鈥檚 neighbours isn鈥檛 really an option.

This may also explain how the Ik got their reputation for selfishness, says Cronk. When anthropologist Colin Turnbull visited in the 1960s, he described them as 鈥渦nfriendly, uncharitable, inhospitable and generally mean as any people can be鈥�. But they had been pushed out of their traditional territory and were struggling with famine and war. Under such circumstances, they may have had little ability to help one another.

However, the ability to help isn鈥檛 enough in itself. To benefit from osotua-style generosity, you need to prevent cheating, for example asking when not truly in need. In some societies the solution is easy. 鈥淚n the context of the Maasai, the things they鈥檙e most concerned with are livestock,鈥� says Cronk. 鈥淚t鈥檚 hard to hide them, so you can鈥檛 cheat.鈥� In addition, osotua requests tend to be made in public, so everyone knows who has asked and given 鈥� or refused to give 鈥� says Sonkoi.

Where wealth is easier to hide, reputation is the key. In Fiji, for example, there is an osotua-like practice called kerekere. 鈥淧eople can get reputations for being habitual kerekere-ers, implying they鈥檙e lazy,鈥� says Matthew Gervais at Rutgers University. That makes them think carefully before making kerekere requests, which bring a slight taint of shame.

In fact, reputation doesn鈥檛 just inhibit cheating in kerekere: it appears to be the rock upon which generosity is built. Gervais gave 51 Fijian men a sum of money roughly equal to a day鈥檚 wages, and the choice of sharing their windfall with any of the other 50 men, all of whom they knew. Despite being told their decision would remain undisclosed, they proved surprisingly generous. On average, they kept just 12 per cent of the money for themselves, and 22 men kept nothing. When Gervais asked them how they chose who to share their money with, almost all said they gave to people who needed it. However, closer statistical analysis showed reputation was almost as important as need. Men with a reputation for giving tended to be the ones who received more.

Cronk believes that in day-to-day life, norms of generosity, love and respect drive decisions about sharing more than cold cost-benefit calculations do. This reinforces the idea that generosity is good. But the Human Generosity Project focuses on close-knit societies. Do humans become less generous when they live in more complex societies?

Of course, there is still need-based giving. 鈥淲hen natural disasters occur, people donate,鈥� says Aktipis. 鈥淎nd they donate because they know there is need, not because they expect they鈥檙e going to get good dividends on their donation to the Red Cross.鈥� On the other hand, people in Western countries often walk past beggars on the street. But that could be because social institutions exist that they expect to step in and help. In fact, Westerners often give generously to strangers, whereas people living in smaller-scale societies tend to direct their generosity towards people they know. Fijians, for example, are very generous within their village. 鈥淏ut when we鈥檝e had Fijians do games that involve giving to distant poor people, they seem almost baffled as to why anyone would send money to someone they don鈥檛 know far away,鈥� says Joseph Henrich at Harvard University.

Nevertheless, osotua-style generosity offers some ideas about how to encourage charitable giving worldwide (see 鈥�Encouraging generosity鈥�). And insights from the Human Generosity Project could help with some seemingly intractable problems. For example, Aktipis is working with the authorities that manage southern Arizona鈥檚 scarce supply of water. The city of Phoenix has dozens of independent water providers that draw from a range of wells and other sources. These vary seasonally and with the weather, so water availability can be unpredictable, leaving individual managers unable to meet demand. Aktipis hopes that by borrowing knowledge from need-based sharing, they will learn to cooperate more effectively.

In the future, this form of generosity could have a far more widespread and important part to play. It is possible that the social upheavals that accompany climate change and sea-level rise could overwhelm conventional insurance and social-assistance programmes. If that happens, it would be comforting to know that we can count on our neighbours for help.

Read more: How does people鈥檚 generosity around the world compare?

A world poll of generosity reveals which countries are best 鈥� and worst 鈥� in the giving stakes. We pick out the most interesting 鈥� how does your nation fare?

This article appeared in print under the headline 鈥淕enerous by nature鈥�