Humans are one of the rare animals to be altruistic. An ancient form of giving holds secrets about why we help one another without any promise of reward. In the Maasai tradition known as osotua – literally, umbilical cord – anyone in need can request aid from their network of friends. Anyone who is asked is obliged to help, often by giving livestock, as long as it doesn’t 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.

Forms of this practice exist all over the world. For instance, Fijians and Tanzanian slum dwellers 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.

This generosity is driven by the unpredictable crisis. It persists because it helps to 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. Disasters cannot be prevented, so need-based giving may have emerged as a proto-insurance policy. If you don’t help others they may not survive, and thus may not be around to help you. They work best when risks are “asynchronous” – when hardship is likely to strike one family and spare their neighbours.

What prevents cheating? The Maasai are most concerned with livestock, which are hard to hide. Furthermore, osotua requests tend to be made in public, so everyone knows who has asked and given – or refused to give. In other cultures reputation is the key. Are you generous, are you just a taker? If you are known as the latter, forget it.

In the Western culture people donate to charities (to people they don’t know personally) because they know there is a need, whereas people living in smaller-scale societies tend to direct their generosity towards people they know.

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 is comforting to know that we can count on our neighbours for help. The number of good causes is bewildering, but if you care about your fellow men you give what you can. This is in the spirit of Epicurus and human decency. My personal favourite is Doctors Without Borders. (based on an article, heavily edited, by Bob Holmes, New Scientist).