There must be something special about us to make possible the distinctively flexible and open-ended communication system of language. Research has focused on our throats, our brains, and our genes, looking for the biological features that allowed for the emergence of language. The Vocal Tract Humans have evolved a very unusual vocal tract with a descended larynx (otherwise known as the “voice box”) and a large and rounded tongue positioned in the mouth to enable a remarkable array of sounds (Lim and Snyder 2015). Some researchers suggest that our throats may have evolved in response to walking upright or changes in diet or a combination of those two factors. Humans also have more deliberate control over breathing than nonhuman primates. In order to better understand when hominins developed this distinct vocal apparatus, researchers examine the hyoid bones of hominins to see if they resemble those of modern humans. The hyoid is a U-shaped bone in the human throat that helps us swallow and move our tongues. The few hyoids that have been found in the fossil record suggest that our distinctive vocal tract may have been developed around 500,000 years ago. This means that Neanderthals likely had the same vocal abilities as modern humans. Figure 6.7 Evolutionary changes in the vocal tract enabled the development of spoken language in humans. The image on the left shows the vocal structures an early ancestor to humans. The image on the right shows the vocal tract of modern humans. The position of the vocal structures in the early ancestor allows for eating and breathing at the same time. The position of these structures in modern humans allows more sounds to be produced and more words to be spoken in sequence. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license) Brain Structure Several features of the human brain are considered prerequisites to language, including the overall (large) size, the division into specialized hemispheres, and certain structures like Broca’s and Wernicke’s areas. Broca’s area is a region of the brain associated with the production of speech. Wernicke’s area is essential to the comprehension of language. Both are most often located in the left hemisphere of the human brain (for left-handed people, both can be located on the right side). How did we acquire these brain features so essential to language? A great deal of controversy surrounds this question, as researchers debate when and how these structures evolved. Figure 6.8 The locations of Broca’s area and Wernicke’s area in the human brain. Broca’s area, responsible for the articulation of speech, is next to the motor area, where the movements of the body are controlled. Wernicke’s area, associated with language comprehension, is situated beside the primary auditory area, where sounds are processed. (credit: “1605 Brocas and Wernickes Areas-02” by OpenStax College/Wikimedia Commons, CC BY 3.0) Most recently, research has focused on “mirror neurons,” special brain cells that seem to enable mimicry (Lim and Snyder 2015). Many researchers think that the ability to understand the actions of others and recreate those actions ourselves is a fundamental prerequisite for language. That is, in order to be able to talk to each other, early hominins must have been able to evaluate and interpret each other’s actions and reproduce them in similar contexts. In primates like monkeys, scientists have discovered a system of specialized neurons called the “mirror neuron system” that enables primates to recognize and imitate actions. Monkeys and apes cannot talk, but they can recognize, interpret, and imitate actions performed by other primates. The neurological studies that revealed mirror neurons are too invasive to perform on humans, but neuroimaging studies suggest that a similar mirror neuron system does exist in humans. Figure 6.9 Mirror neurons are most likely involved in the spread of contagious yawning. Mirror yawning happens between humans and can even happen across species. You can make your dog yawn! (credit: “Sleepy” by Toshimasa Ishibashi/flickr, CC BY 2.0) Brain imaging studies on humans have located evidence for the mirror neuron system in a region of the brain close to Broca’s area. So it is possible that the mirror neuron system inherited from primates provided a foundation for the later emergence of a brain structure devoted to language production in hominins. If imitation and language are in fact connected in this way, then a system of gestures may have paved the way for the development of language. Some researchers now hypothesize exactly this: that hominin language evolved from a system of gestures to a system of vocalizations. The “Language Gene” In the late 1980s, medical researchers became aware of a particular speech disorder common among members of one family in West London. Many members of this family could not pronounce words. Many stuttered. Many had very limited vocabularies. Geneticists traced the disorder to a genetic mutation on chromosome number 7 of the human genome. (See Biological Evolution and Early Human Evidence for more on chromosomes and genes.) The mutation was located on a gene named FOXP2, prompting some researchers to dub this “the language gene.” Some hypothesize that FOXP2 may have played a role in the development of language in humans (Lim and Snyder 2015). At first, researchers thought that only humans had the FOXP2 gene, but subsequently a form of this same gene has been identified in many vertebrates, including mice, bats, fish, and songbirds. In mice, the gene appears to be related to vocalizations. In birds, it seems to be linked to birdsong. All primates have FOXP2, but the human copy is slightly different than that of nonhuman primates. Some researchers think this mutation occurred around 260,000 years ago and may have enabled the development of spoken language in Neanderthals and Homo sapiens. Other researchers are skeptical of the notion that one gene could be responsible for the emergence of spoken language (Tallerman and Gibson 2011). Many anatomical developments and cognitive processes—connected to different parts of the human genome—are involved in human language. These developments and changes would have required mutations in other parts of the genome of early Homo. While the mutation of FOXP2 in Homo may have played a role in language development, other mutations would have been important as well.