In his seminal work, Chomsky (1996: 41) declared that ‘Organs develop to serve one purpose, and when they have reached a certain form in the evolutionary process, they became available for different purposes, at which point the processes of natural selection may refine them further for these purposes.’ For instance, despite the main purposes of the fingers, fingers might serve other purposes such as communication with others. For example, a thumb up for OK, pointing to a place or an object and gesture of sign language (Tellier, 2009). The author considers that ‘language is part of shared biological endowment’ both inputs and outputs of the language might be considered in the way of other biological systems (Luciano, Fadiga, Roy, Fazio &Craighero, 2007) ‘as a product of natural selection’. In other words, language is the product of natural creation. Chomsky (1996), nevertheless, suggests that the evolutionary theory might not be applicable so far on language matters. Language acquisition and verbal communication might be facilitated by non-verbal gestures due to the fact that they play an important role (Capirci&Volterra, 2008; Kelly, Özyürek, & Maris, 2010; Rowe & Goldin-Meadow, 2009; Rowe, Özçaliskan& Goldin-Meadow, 2008; Skipper, Wassenhove, Nusbaum, & Small, 2007; Pizzuto& Capobianco, 2005). Moreover, it is worthwhile to remember that language and non-verbal gestures are different in terms of structure and representation (Kelly, 2003; Tellier, 2009; Wolla&Sieratzkib, 2003). Despite the fact that the difference between non-verbal gestures (Bates & Dick, 2002; Feyereisen, 2007; Goldin-Meadow, Iverson &Thelen, 1999; 2003; Tellier, 2009; Volterra, Caselli, Capirci&Pizzuto, 2005) and speech is preserved and they can work together but separately, the process of producing the language is reflected in a variety of forms which are different from non-verbal gestures (Furuyama, 2002; McNeill, 1992, 2000). From another perspective, non-verbal gestures and speech are strongly connected (Bates & Dick, 2002; Bernardis&Gentilucci, 2006; Capirci&Volterra, 2008; Capone & McGregor, 2004; Cochet&Vauclair, 2010; Corballis, 2003; Dohen, 2009; Kelly, 2003; Iverson &Thelen, 1999; Rochet-Capellan et al., 2008; Rowe & Goldin-Meadow, 2009; Rowe, Özçaliskan& Goldin-Meadow, 2008; Skipper, Goldin-Meadow, Nusbaum, Small, 2007; Pizzuto& Capobianco, 2005). According to other researchers non-verbal gestures and speech functions are inter-connected (Capone & McGregor, 2004; Goldin-Meadow, 2003: 2009; Kelly et al., 2010; McNeill, 1992). Tellier (2009) suggests that the connection and inter-connection between non-verbal gestures and speech can explicitly be seen from the natural conversation which occurs with people, whereas the non-verbal gesture is accompanied with discourse. Nonetheless, non-verbal gesture aids listeners to understand the meaning of words that is attributed to help in conveying ideas, meaning, codifying words and grammatical devices (Goldin-Meadow, 2009). However, the understanding of information depends upon whether the non-verbal gesture and speech convey the same information. Although this process is faster, it may generate a few errors (Kelly, Özyürek& Maris, 2010; Tellier, 2009). In relation to this aspect, Iverson and Goldin-Mead (1998) argued that people can make non-verbal gestures even when they speak to blind listeners. Therefore, it can be concluded that the non-verbal gesture does not only convey information to listeners but also can help speakers to understand the message properly. For this reason we gesture when we speak on the phone. Pine, Lufkin, Kirk, and Messer (2007) hypothesis a high degree of semantic synchrony between gestures and spoken language is expected. Moreover, semantic synchrony gives a support meaning to the speech when non-verbal gesture is used and helps in expressing the same idea (Cornejo et al., 2009; Kelly et al., 2004, 2007; Kendon, 2004; McNeill, 2005; Özyürek et al., 2007). It can also be provided by the non-verbal gesture when used with spoken language which may improve language comprehension (Goldin-Meadow, 2003; McNeill, 1992; Rochet-Capellan, Laboissière, Galván& Schwartz, 2008).

There are a variety of ways in which the non-verbal gesture can play the role of facilitator in language comprehension such as retrieving words from one’s mind (Butterworth &Hadar 1989) and thus facilitate access to lexical affiliates (Feyereisen, 2006; Krauss &Hadar, 1999). Morford and Goldin-Meadow (1992) developed what is merely called hand gestures which helps children aged 1-2 years to understand what adults say, while the hand gesture helps toddlers to understand more complex communication (Kelly, 2001). The presence of the non-verbal gesture can help in the elimination of speech ambiguity (Holler & Beattie, 2003). This means that non-verbal gesture not only helps eliminate ambiguity but the non-verbal gesture also has meaning (Kelly et al., 1999). According to Capone and McGregor (2004), non-verbal gestures can do more than that and aid in supporting the performance of more complex activities such as language comprehension.

As aforementioned, non-verbal gestures and speech are closely related and are synergetic (McNeill 1985; 1992; 2005). The occurrence of the non-verbal gesture and speech takes place in natural discourse (Feyereisen, 2007). Despite interrelated synergy between them, the non-verbal gesture occurs before vocalisation from which we can conclude that the non-verbal gesture aids speakers to organise their ideas and information in their mind and conceptualise them for verbalisation (Bernardis&Gentilucci, 2006; Kendon, 2004; Morrel-Samuels & Krauss, 1992). Alibali et al., (2000: 610) conclude that ‘the action of gesturing helps speakers to organise spatial information for verbalisation, and in this way, the non-verbal gesture plays a role in conceptualising the message to be verbalised’. In her experimental study on vocalisation, Feyereisen (2007) argued that slow vocal responses are associated with slower manual responses. However, there are some non-verbal gestures which help decrease cognitive loads during explanation of words for example, speakers remembered more when they gestured than when they did not gesture (Goldin-Meadow et al., 2001).

There has been consensus upon the relationship between non-verbal gesture and speech. Goldin-Meadow and Morford (1985: 146) observed that ‘…communication in humans is a resilient phenomenon; when prevented from coming out the mouth, it emanates almost irrepressibly from the fingers’. Individuals usually gesture during speaking while they move their hands, heads, arms and the whole body are involved in communication. Therefore, it can be stated that non-verbal gestures, speech and language are strongly connected in the following aspects: developmentally (Capone & McGregor, 2004; Tellier, 2009), neurologically (Bates & Dick, 2002; Iverson &Thelen, 1999: 20) and behaviourally (Mayberry &Jaques, 2000; Mayberry &Shenker, 1997; van Lieshout, 2004).