Humans were once united by the belief that you should never, ever point at one.
When a rainbow appeared in the sky over Tugu, a neighborhood in Jakarta, Robert Blust did what came naturally: he pointed to it. The year was 1980, and Blust, then a professor at the University of Leiden in the Netherlands, was waiting for lunch with a group of teachers from around Indonesia.
One of the teachers, seeing Blust’s gesture, politely informed him that, in Sumatra, pointing to rainbows was considered a no-no. Another chimed in to say the same was true where he came from, in a different part of the archipelago. Both had learned as children that if you broke the taboo, your finger would become bent like a rainbow.
The incident did not affect Blust’s finger, but it did bend the arc of his career. He’d stumbled on a puzzle that would occupy him on and off for the next forty years.
When Blust returned to the Netherlands, he was still thinking about the incident. “Something about the experience stayed in my mind,” he later wrote. He started combing ethnographies for traditional beliefs about rainbows. The first hint that he was on to something bigger, something truly boggling, came from a report of a prohibition on pointing to rainbows in India. “It did not take long for the shock to set in,” he wrote. The report suggested “the rainbow taboo”—as he would come to call the phenomenon—was not confined to Southeast Asia.
Blust began to cast a wider net. He sent questionnaires to colleagues and missionary stations around the world, inquiring about rainbows and taboos related to them. He would soon amass evidence for the rainbow taboo—in some form or another—in 124 cultures.
The prohibition turned up in North America, among the Atsugewi of northern California and the Lakota of the northern plains; in remote parts of Australia and isolated islands in Melanesia; among the Nyabwa of Ivory Coast and the Kaiwá of Brazil. At one time it was present in Europe, too: one of the Grimm brothers noted it in his book on German mythology. The belief was not found in every culture, according to Blust’s search, but it was present globally, across all inhabited regions.
There was also more to the taboo than the vague idea that pointing to rainbows is bad. Blust found that it often came bundled with specific ideas about what would happen if you violated the taboo, ideas that varied from culture to culture. Most commonly, your finger would suffer the consequences: it might become bent or paralyzed, fall off, wither, rot, or swell, or develop warts, ulcers, or maggots. Less commonly—such as in parts of New Guinea and Australia—the ill effects would befall your mother.
In most cases, it was specifically pointing with the index finger that was prohibited. It was fine to draw attention to a rainbow using your head, lips, nose, or tongue, or by forming your hand in a less “pointy” shape, such as a fist. A final recurring idea was that, should you accidentally point to a rainbow, there were remedies. You could wet the offending digit; or put it into a bodily cavity like your mouth, anus, or belly button; or, according to the Javanese version of the taboo, plunge it into a pile of buffalo dung.