What hand gestures tell us about the evolution of language

Suzanne Aussems — Post-Doctoral Fellow/Early Career Fellow, Language & Learning Group, Department of Psychology, University of Warwick

Imagine that you are vis­it­ing a food mar­ket abroad and you want to buy a slice of cake. You know how to say “hello” in the nat­ive lan­guage, but oth­er­wise your know­ledge of the lan­guage is lim­ited. When it is your turn to order, you greet the vendor and point at the cake of your choice. The vendor then places his knife on the cake and looks at you to see if you approve of the size of the slice. You quickly shake both of your hands and indic­ate that you would like a smal­ler width for the slice using your thumb and index fin­ger. The vendor then cuts a smal­ler piece for you and you hap­pily pay for your cake. In this example, you achieved suc­cess­ful com­mu­nic­a­tion with the help of three ges­tures: a point­ing ges­ture, a con­ven­tion­al ges­ture, and an icon­ic gesture.

As humans, we are the only spe­cies that engage in the com­mu­nic­a­tion of com­plex and abstract ideas. This abstract­ness is even present in a seem­ingly simple example such as indic­at­ing the size of a slice of cake you desire. After all, size con­cepts such as ‘small’ and ‘large’ are learnt dur­ing devel­op­ment. What makes this sort of com­mu­nic­a­tion pos­sible are the lan­guage and ges­tures that we have at our dis­pos­al. How is it that we came to devel­op lan­guage when oth­er anim­als did not, and what is the role of ges­ture in this? In this blo­g­post, I intro­duce one his­tor­ic­ally dom­in­ant the­ory about the ori­gins of human lan­guage – the gesture-primacy hypo­thes­is (see Hewes, 1999 for an his­tor­ic overview).

According to the gesture-primacy hypo­thes­is, humans first com­mu­nic­ated in a sym­bol­ic way using ges­ture (e.g. move­ment of the hands and body to express mean­ing). Symbolic ges­tures are, for example, pan­to­mimes that sig­ni­fy actions (e.g., shoot­ing an arrow) or emblems (e.g., rais­ing an index fin­ger to your lips to indic­ate “be quiet”) that facil­it­ate social inter­ac­tions (McNeil, 1992; 2000). The gesture-primacy hypo­thes­is sug­gests that spoken lan­guage emerged through adapt­a­tion of ges­tur­al com­mu­nic­a­tion (Corballis, 2002, Hewes, 1999). Central to this view is the idea that ges­ture and speech emerged sequen­tially.

Much of the evid­ence in favour of the gesture-primacy hypo­thes­is comes from stud­ies on non­hu­man prim­ates and great apes. Within each mon­key or ape spe­cies, indi­vidu­als seem to have the same basic vocal rep­er­toire. For instance, indi­vidu­als raised in isol­a­tion and indi­vidu­als raised by anoth­er spe­cies still pro­duce calls that are typ­ic­al for their own spe­cies, but not calls that are typ­ic­al for the foster spe­cies (Tomasello, 2008, p. 16). This sug­gests that these vocal calls are not learned, but are innate in non­hu­man prim­ates and great apes. Researchers believe that con­trolled, com­plex verbal com­mu­nic­a­tion (such as that found in humans) could not have evolved from these lim­ited innate com­mu­nic­at­ive rep­er­toires (Kendon, 2017). This line of think­ing is partly con­firmed by failed attempts to teach apes how to speak, and failed attempts to teach them to pro­duce their own calls on com­mand (Tomasello, 2008, p. 17).

However, the rep­er­toire of ape ges­tures seems to vary much more per indi­vidu­al than the vocal rep­er­toire (Pollick & de Waal, 2007), and research­ers have suc­ceeded in teach­ing chim­pan­zees manu­al actions with the help of sym­bol­ic ges­tures that were derived from American Sign Language (Gardner & Gardner, 1969). Moreover, bonobos have been observed to use ges­tures to com­mu­nic­ate more flex­ibly than they can use calls (Pollick & de Waal, 2007). The degree of flex­ib­il­ity in the pro­duc­tion and under­stand­ing of ges­tures, espe­cially in great apes, makes this com­mu­nic­at­ive tool seem a more plaus­ible medi­um through which lan­guage could have first emerged than vocalisation.

In this regard, it is not­able that great apes that have been raised by humans point at food, objects, or toys they desire. For example, some human-raised apes point to a locked door when they want access to what’s behind it, so that the human will open it for them (Tomasello, 2008). It is thus clear that human-raised apes under­stand that humans can be led to act in bene­fi­cial ways via attention-directing com­mu­nic­at­ive ges­tures. Admittedly, there does seem to be an import­ant type of point­ing that apes seem incap­able of; namely, declar­at­ive point­ing (i.e., point­ing for the sake of shar­ing atten­tion, rather than merely dir­ect­ing atten­tion) (Kendon, 2017). Nonetheless, ges­ture seems to be a flex­ible and effect­ive com­mu­nic­at­ive medi­um that is avail­able to non-human prim­ates. This fact, and the fact that vocal­isa­tions seem to be rel­at­ively inflex­ible in these spe­cies, play a sig­ni­fic­ant role in mak­ing the gesture-primacy hypo­thes­is a com­pel­ling the­ory for the ori­gins of human language.

What about human evid­ence that might sup­port the gesture-primacy hypo­thes­is? Studies on the emer­gence of speech and ges­ture in human infants show that babies pro­duce point­ing ges­tures before they pro­duce their first words (Butterworth, 2003). Shortly after their first birth­day, when most chil­dren have already star­ted to pro­duce some words, they pro­duce com­bin­a­tions of point­ing ges­tures (point at bird) and one-word utter­ances (“eat”). These ges­ture and speech com­bin­a­tions occur roughly three months before pro­du­cing two-word utter­ances (“bird eats”). From an onto­gen­et­ic stand­point, then, ref­er­en­tial beha­viour appears in point­ing ges­tures before it shows in speech. Many research­ers there­fore con­sider ges­ture to pave the way for early lan­guage devel­op­ment in babies (Butterworth, 2003; Iverson & Goldin-Meadow, 2005).

Further evid­ence con­cerns the spon­tan­eous emer­gence of sign lan­guage in deaf com­munit­ies (Senghas, Kita, & Özyürek, 2004). When sign lan­guage is passed on to new gen­er­a­tions, chil­dren use rich­er and more com­plex struc­tures than adults from the pre­vi­ous gen­er­a­tion, and so they build upon the exist­ing sign lan­guage. This phe­nomen­on has led some research­ers to believe that the devel­op­ment of sign lan­guage over gen­er­a­tions could be used as a mod­el for the evol­u­tion of human lan­guage more gen­er­ally (Senghas, Kita, & Özyürek, 2004). The fact that deaf com­munit­ies spon­tan­eously devel­op fully func­tion­al lan­guages using their hands, face, and body, fur­ther sup­ports the gesture-primacy hypo­thes­is.

Converging evid­ence also comes from the field of neur­os­cience. Xu and col­leagues (2009) used func­tion­al MRI to invest­ig­ate wheth­er sym­bol­ic ges­ture and spoken lan­guage are pro­cessed by the same sys­tem in the human brain. They showed par­ti­cipants mean­ing­ful ges­tures, and the spoken lan­guage equi­val­ent of these ges­tures. The same spe­cif­ic areas in the left side of the brain lit up for map­ping sym­bol­ic ges­tures and spoken words onto com­mon, cor­res­pond­ing con­cep­tu­al rep­res­ent­a­tions. Their find­ings sug­gest that the core of the brain’s lan­guage sys­tem is not exclus­ively used for lan­guage pro­cessing, but func­tions as a modality-independent semi­ot­ic sys­tem that plays a broad­er role in human com­mu­nic­a­tion, link­ing mean­ing with sym­bols wheth­er these are spoken words or sym­bol­ic gestures.

In this post, I have dis­cussed com­pel­ling evid­ence in sup­port of the gesture-primacy hypo­thes­is. An intriguing ques­tion that remains unanswered is why our closest evol­u­tion­ary rel­at­ives, chim­pan­zees and bonobos, can flex­ibly use ges­ture, but not speech, for com­mu­nic­a­tion. Further com­par­at­ive stud­ies could shed light on the evol­u­tion­ary his­tory of the rela­tion between ges­ture and speech. One thing is cer­tain: ges­ture plays an import­ant com­mu­nic­at­ive role in our every­day lives, and fur­ther study­ing the phylo­geny and onto­geny of ges­ture is import­ant for under­stand­ing how human lan­guage emerged. And it may also come in handy when order­ing some cake on your next holiday!



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