Out of the billions of neurons in the monkey brain, there is a single neuron that is activated only by the sound of a breaking peanut. This neuron does not activate when the monkey sees the peanut, tastes the peanut, or holds the peanut; it only activates when hearing the sound of a breaking peanut, either by itself or another individual (Kohler et al., 2002). This sensation is created by the mirror-neuron system, which is a class of neurons that activate when the individual itself performs an action or when another individual performs the same action (Fogassi & Ferrari, 2007).
This neural connection between perception and motor control could help settle the debate of how human language evolved. One hypothesis is that human language evolved from nonhuman primate gestures and vocal communication, and the opposing hypothesis is that human language was independently acquired by the human species (Hauser, Chomsky, & Finch, 2002).
The mirror-neuron system is found in the pre-motor cortex of monkeys. Motor neurons are also found in this cortex, and are activated when engaging in goal-directed tasks, including holding, manipulating, or reaching for an object (Rizzolatti & Craighero, 2004). This pathway can translate sensory information, such as seeing an object, into motor knowledge, by reaching for the object. Because this all happens in the same area of the monkey’s brain (pre-motor area F5), this demonstrates the anatomical relationship between perception and motor action. These neurons also activate when the monkey does a certain motor action, and when the monkey perceives another individual performing the same action. For example, when a monkey sees another monkey grasping food for eating it, this activates the same neural system that corresponds to that action, and the goal associated with it. Therefore, activating the goal that is linked to the perceived gesture can help the receiver understand the message of the sender (Fogassi & Ferrari, 2007). This suggests that the mirror-neuron system may provide evidence of how human language evolved from gestures and vocalizations.
One way to address the evolution of language is to examine the anatomical similarities between humans and our closest nonhuman primate. Many studies have shown that area 44 (Broca’s area), or the “speech” area of the human brain, has many anatomical parallels to area F5 in the monkey brain (Rizzolatti & Arbib, 1998). The first similarity between both these areas is that area F5 in the monkey brain is composed of motor neurons that control hand and mouth movement, and area 44 in the human brain is responsible for complex hand movement and mental imagery tasks such as grasping objects (Rizzolatti & Craighero, 2004). Additionally, the mirror-neuron system is located in both of these areas. This suggests that the mirror-neuron system is directly related to the “speech” area of the human brain, and the anatomical similarities provide evidence that spoken language may have evolved from these areas of the brain.
In addition to anatomical similarities between the communicative parts of the brains, another reason spoken language may have developed in humans is because combining gestures as well as calls has been proven to send more efficient messages among members of the same species (Fogassi & Ferrari, 2007). There are two aspects that allow the coupling of gestures and vocalizations in humans to produce more effective messages. First, many nonhuman primates have a limited amount of vocalizations they can express because of anatomical restraints, but humans have the physical ability for fine motor control of the larynx (Ridley, 2003). Second, most nonhuman primate call productions stem from immediate danger or intense emotional states, whereas humans use vocalizations for a variety of types of communication. A similarity between both forms of communication is the use of body postures and gestures of the face and forelimbs (Fogassi & Ferrari, 2007). This information suggests that spoken language may have developed because of the efficiency of coupling gestures and vocalizations. Additionally, humans are able to capitalize on this efficiency because we possess the ability to create a variety of communicative messages because we lack the anatomical constraints that nonhuman primates have.
In order to achieve successful communication between two individuals, both must share similar motor programs and pathways to produce a message (Fogassi & Ferrari, 2007). Humans have developed an efficient way of sending messages through progressive gestures and the use of spoken language. The mirror-neuron system has provided evidence that human language evolved from nonhuman primate gestures and vocal communication through studying the anatomical and behavioral similarities of the nonhuman primate and human forms of communication.
References:
Hauser, M.D., Chomsky, N., & Fitch, W.T. (2002). The faculty of language: What is it, who has it, and how did it evolve? Science, 298, 1569–1579.
Kohler, E., Keysers, C., Umilta, R.A., Fogassi, L., Gallese, V., & Rizzolatti, G. (2002). Hearing sounds, understanding actions: Action representation in mirror neurons. Science, 297, 846–848.
Ridley, M. (2003). The Agile Gene. New York, NY: Harper Collins Publishers Inc.
Rizzolatti, G., & Arbib, M.A. (1998). Language within our grasp. Trends in Neurosciences, 21, 188–194.
Rizzolatti, G., & Craighero, L. (2004). The mirror-neuron system. Annual Review of Neuroscience, 27, 169–192.
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