Almost everywhere in the world, people shake their heads when they want to say "no". Even the British naturalist Charles Darwin questioned why people from very different cultures shake their heads to signify negation. Darwin came up with a spectacular hypothesis. The widespread use of shaking our heads might have a very natural origin:
“With infants, the first act of denial consists of refusing food; and I repeatedly noticed with my own infants, that they did so by withdrawing their heads laterally from the breast, or from anything offered them in a spoon. In accepting food and taking it into their mouths, they incline their heads forwards.”Charles Darwin, 1872: “The Expression of the Emotions in Man and Animals”
In fact, Darwin's reasoning is one of the few explanations for why people shake to signify rejection. And the idea is plausible: children are born with a sucking reflex. When a child has satisfied its hunger at its mother's breast, it must then stop sucking - and this is done by an evasive movement, since the sucking reflex cannot simply be switched off.
Because children have little motor control of their hands at the beginning, and moving the head backwards is usually not possible because the head is supported by the mother's hand or arm due to weak neck muscles, the child only has one option, namely, to turn its head to the side. This, of course, also applies to other types of feeding, i.e., when the child is being fed and not breastfed. It is plausible to assume that such an early childhood association results in a conventionalized gesture. After an association has been made between the sideways movement of the head and rejection, it is only a small step to repeat this sideways movement for reinforcement and to extend the meaning generally to signify negation.
But is this really the case?
The problem with Darwin's hypothesis is that it is difficult to prove scientifically. Bross suggests, it might not be possible to test the hypothesis directly, but it is possible to test the expectations of behavior that arise from the hypothesis. If Darwin's theory is correct, then we can consider the following:
- The gesture is extremely widespread because it is of natural origin. However, the gesture is not innate, which means that there is still the possibility that it has been "overwritten" by another gesture in some cultures.
- According to Darwin, the gesture arises from an association at an extremely early stage of childhood, which means that even very young children would shake their heads to express negation.
- Even people who are not capable of observing gestures should have head shaking in their repertoire of gestures. Specifically, people who are born deaf and blind.
- The association of food intake and head movement is not necessarily restricted to humans. In theory, all mammals that have a concept of negation and are nursed in a similar way should also shake their heads.
The prevalence of head shaking
The first question is, where in the world do people shake their heads to say “no”. “There is virtually no study that has systematically investigated the prevalence of head shaking. At the same time, you'd think that if someone had gone traveling in earlier times and found that people in a faraway country didn't shake their heads to say 'no', but used a different gesture, that they would have found that interesting and written that down," says Bross. In fact, he found few reports of other gestures.
Head shaking in Bulgaria, Greece, or Turkey
In a few regions of the world, a shake of the head means “yes”, and a nod of the head means "no." However, this "back-to-front" system is extremely rare and is most prominently found in Bulgaria. Another option is to throw your head back quickly and click your tongue to express "no." This gesture is prevalent in South Italian and in some part of Greece and Turkey. Bross says, "It is striking that the few exceptions form clusters". "This makes it probable that these gestures originate from something and were then passed down culturally. It is also interesting that it has so far been overlooked in the literature that the cultures that recognize this 'Greek no' may well also use a head shake."
Head shaking in sign language
Further data has confirmed that a shake of the head is understood in almost all cultures with very few exceptions, and also that it was understood in earlier times. “There are hardly any studies that explore how widespread head shaking is, as a gesture that accompanies speech, but there are many studies that investigate head movements in sign languages across the world. All sign languages that have been investigated so far, use some kind of head shaking gesture to express negation – all over the world.” The question is, how did head shaking become part of all these sign languages.
At what age do we begin to shake our heads?
If Darwin's theory is correct, a further expectation would be that the gesture of head shaking must be acquired at a very early age. And, in fact, head shaking is one of the first gestures ever used by children. Interestingly, at the earliest stage, shaking the head is used only as a gesture of rejection and a purely logical negative meaning is added later.
Do people who are born deaf and blind also shake their heads?
If it is correct that there is a natural connection between head shaking and negation, then one would predict that people who could not observe the gesture would also use it. For example, studies that have investigated the use of gestures by deaf-blind children do actually show that they shake their heads when you try to give them an object they don't want. However, studies in this area are rather scarce and it is possible that the children who participated in the previous studies were implicitly taught to shake their heads in some way.
Do other mammals shake their heads?
Concerning Darwin's theory, the final expectation concerns animals that suckle their children in a similar way to humans. Assuming they have an understanding of negation, these animals should also make a connection between the sideways movement of the head and negation. Only a small set of mammals come into question here, since the majority of mammals suckle their infants while lying or standing, which does not require a sideways movement of the head. Nevertheless, some monkey species suckle their children in a similar way to humans. Unfortunately, the studies that have investigated this are not of a very high standard. The few studies that explore monkey head gestures suggest that some monkey species rarely use their heads for communication. But bonobos, at least, have been observed to acknowledge unwanted behavior with a shake of the head, and there is even convincing video footage of this.
Dr. Fabian Bross researches and teaches at the Institute of Linguistics/German Language and Literature Studies at the University of Stuttgart. His work investigates the grammar of German sign language, with speech-accompanying gestures in German, and with the interface between speech and thought.
Darwin's hypothesis that shaking the head originates from an association in early infancy is difficult to prove. It is, however, possible to test the expectations that arise from the hypothesis, and these seem to be largely accurate, despite the fact that research into gestures used by people who are born deaf and blind is still in its infancy, and results on gesture used by monkeys, at least for some species, are not entirely conclusive.