Various aboriginal communities lived in the rainforest of north-eastern Australia, surrounded by waterfalls, short rivers and swamps. They lived off hunting, fishing and gathering. Some tribes inhabited the coastal areas and would ascend to the tablelands in the wet season, to avoid the extremely hot, humid, insect-ridden coastal flats. Other tribes occupied these tablelands, and would descend to the coast in the winter, to avoid the mountain frosts and mists.

The languages they spoke are known as Dyirbal, Yidiñ and Warrgamay. Their oral heritage included stories of the origin of everything. Many of the animals had originally been people, according to their legends. They held corroborees, regular events at which songs would be played, marriages arranged and, amidst dance and music, grievances would be settled by single combat. But not everything was pleasure and jollity. They practised cannibalism, though in a mild form. People were never killed in order to be eaten, but the grave of a recently deceased person from a neighbouring tribe could be raided sometimes, and the body consumed. Or a local person found guilty of a serious crime could be killed, the flesh eaten and the blood given to young men to drink.

A truly exotic feature of all Australian aboriginal communities is their kinship system, which determines every sort of social responsibility, such as who you can and cannot marry, become friends with or joke around with, and who is obligated to organise a boy’s initiation or a relative’s funeral. The children of mothers’ sisters’ and fathers’ brothers (parallel cousins) are regarded as equivalent to one’s own siblings, whereas those of mothers’ brothers and fathers’ sisters (cross cousins) must never be directly addressed, and a different speech style ought to be used when talking in their presence. They are regarded as potential wives and husbands.

The weirdest people in the world?

In a now well-known paper published in 2010, psychologists Joseph Henrich, Steven Heine and Ara Norenzayan expressed their concern that many experimental studies in the behavioural sciences were performed on human populations who are outliers in many psychological domains. Those are—they coined the term—WEIRD populations, i.e. Western, educated, industrialised, rich, and democratic. They write,

For the vast majority of its evolutionary history, humans have lived in small-scale societies without formal schools, governments, hospitals, police, complex divisions of labour, markets, militaries, formal laws or mechanized transportation. Every household provisioned much or all of its own food; made its own clothes, tools and shelters; and—aside from sexual divisions of labour—almost everyone had to master the same skills and domains of knowledge. Children typically did not grow up in small, monogamous nuclear families with few kin around, nor were they away from their families at school for much of the day.

It isn’t safe to make generalisations from human samples that are hardly representative of all humankind. Take grammatical gender. One common feature of many European languages is the distinction between masculine and feminine nouns—a few languages (for instance, German, Russian and Greek) add also a third category, neuter. Yet this is far from being a universal property of the gender systems of recorded languages across the world. More than half lack any gender at all. Of those that do have gender, the most common options are two genders, followed by three, but some have four, five or even more. Swahili, for instance, has eight genders, and Dyirbal, mentioned above, has four.

Cross-cultural research can deepen our understanding of human psychology. It can dispel our Eurocentric biases. Some have written that invisible friends, for instance, “are a common manifestation for many kids across many stages of development,” and research carried out in the US has shown that around 67% of children had had at least one invisible friend by age seven. This rate, however, contrasts starkly with that of other countries. A study carried out in Kenya, Nepal, Malawi and the Dominican Republic showed that hardly any Nepali children had had an invisible friend, and only 34% of Dominicans had (the highest rate for that group of countries).

Take also social discounting, a preference for benefitting closer individuals over more distant ones, even at great cost to oneself. WEIRD people usually give more money and other social resources to partners who are close to them socially, but that is not the case in some non-WEIRD societies. While US subjects adjusted their decisions in accordance with social distance (giving more resources to close individuals, less to distant ones), some researchers have found that Bangladeshi and Indonesian subjects did not show any signs of social discounting. They valued distant people in greater need more than less needy people closer to them.

The second benefit of expanding our research to encompass non-WEIRD societies is that it encourages us to recognise human diversity and shows how culture may influence developmental pathways.

Consider the sense of fairness. Researchers compared responses to disadvantageous inequity (when your peers receive more than you) and advantageous inequity (when you receive more than your peers) among seven different societies. Previous research had shown that, in western populations, children displayed disadvantageous inequity aversion by four years of age, whereas advantageous inequity aversion didn’t appear until they were about eight years old. Little was known about whether other human societies followed similar developmental trajectories—until now. The team tested children from four to fifteen years old and discovered enormous variation. Although disadvantageous inequity aversion appeared in all seven societies, children reacted to a disadvantage by four and five years of age in the US and Canada, but not until the ages of eight and ten in India and Mexico, respectively. In all groups except the Mexican one, disadvantageous inequity aversion grew stronger with age. Advantageous inequity aversion, by contrast, emerged only in the US, Canada and Uganda, where it also grew stronger with age, but was absent in the other societies.

Advantageous inequity aversion clearly requires some degree of prosocial behaviour. Recent research has revealed more about its nature. Using tasks to assess the generosity of individuals when it was personally costly for them to deliver rewards to peer recipients (costly sharing game) and when it cost them nothing to confer benefits on recipients (prosocial game), researchers found that American children show prosocial tendencies at age three and their frequency rises with age, but Fijian children behave prosocially at age three, but become more selfish as they grow older. Additional research on early prosocial behaviour that compared German and Ugandan children found that German four to seven-year-olds share more with friends than with non-friends, but Ugandan children show no preference.

We must be grateful to those who are willing to make sacrifice to help us, and yet be careful to remember that verbalising gratitude is not as frequent in other cultures as it may be in ours. “The idea that gratitude’s role in social reciprocity is tied to saying ‘thank you’ appears to be largely based not on systematic empirical observation but on attitudes about politeness in English-speaking society,” some authors have pointed out. By comparing audio-visual recordings across eight different languages, they found that expressing gratitude was common in English and Italian, but rare in Russian and Polish (three of the other four languages were aboriginal, and the fourth was the official language of Laos: in all these, verbalising gratitude was also rare).

Isn’t it rude not to say thank you? Not really. There are at least three main ways to express gratitude. In addition to verbal expressions of gratitude, concrete expressions of gratitude involve reciprocation, by offering something of interest to the beneficiary, rather than the benefactor, and connective gratitude involves reciprocating with something of interest to the benefactor. All cultures display these three forms of gratitude at different relative frequencies. How common or uncommon is each form? To find out, researchers compared children in seven countries. Their results are depicted in the figure below. (The size of the circles represents the extent to which children verbalised gratitude). As you can see, China showed the highest rates of connective gratitude, Brazil the lowest. The US had the highest levels of concrete gratitude. Guatemala had the lowest rates of concrete gratitude, but the highest rates of verbal gratitude, South Korea the lowest.

What else can we learn from cross-cultural approaches? That people in some societies judge harmful actions as more intentional than altruistic ones. In one study, the researchers observed this in Mexico, the US and South Korea, but found the pattern reversed in Samoa and Vanuatu. In these two cultures, people didn’t think a person would intentionally harm the environment, for example, but believed they would intentionally benefit it. They also conceived of altruistic actions as more praiseworthy than harmful actions were blameworthy.

Psychology has much to gain from a broader perspective on human nature. However, true cross-cultural research has yet to be undertaken. An analysis of the articles published in two leading evolutionary psychology journals between 2015 and 2016 revealed that the majority of samples came from North America, followed by Europe and Asia. Among nearly 300 samples, only 6 came from Africa and 8 from Latin America and the Caribbean; there were 7 samples from Australia and 1 from Oceania. “Combining the figures,” the authors summarised, “we found that around 8 out of 10 samples were from WEIRD populations (81%, Europe/North America/Australia), and that 87% of the samples used were from developed regions.” Another analysis concluded that three quarters of all studies published in 2017 neglected to discuss the possible effects of culture and context on their findings, and over 70% of samples were from North America, Europe and Australia, samples from Asia comprised less than 7%, and not a single study sampled people from Africa, the Middle East or Latin America.

It’s now possible to assess the WEIRD-ness of a society using a cultural distance scale, which measures the distance of a country relative to the US (the WEIRD country by default) and China (the most cited country in cultural research comparisons, for which a Sino scale was developed). However, it’s obvious that we’re still far away from a psychology that is truly representative of our whole species. As some experts have highlighted, “Failure to understand what is species and/or culturally specific leaves a possibly skewed, potentially inaccurate and certainly incomplete picture. It is time for a new approach to developmental psychology that fully integrates contemporary research efforts spanning WEIRD populations” as well as non-WEIRD ones.