More than 7,000 languages exist today, a wealth of diversity that continues to puzzle researchers. Languages vary in a number of ways: Parts of speech, for instance, may be ordered differently. And a change in tone can signify a distinct word meaning. One lingering question that has perplexed linguists is whether genes predispose the use of tones or other linguistic features.
A study published last month in Science Advances suggests subtle DNA differences influence a person’s ability to perceive tones. It provides the first tangible evidence for the potential impact of genes in the evolution of language.
“For the first time, we found direct evidence that a genetic variant is actually tied to a linguistic feature,” says Patrick Wong, a cognitive neuroscientist at the Chinese University of Hong Kong and lead author of the paper. This insight, he adds, carries important practical implications for those with language impairments.
Wong and his colleagues are not the first to hypothesize that genetic diversity may drive the evolution of language. In 2007 researchers compared two dozen linguistic features to nearly 1,000 gene variants in 49 populations around the world. They found a significant correlation between the presence of separate variants in the genes ASPM and MCPH1 and an increased likelihood that a group speaks a language that uses pitch to change words’ meaning. Such tonal languages —spoken in China, Southeast Asia and Central Africa, among other regions—make up at least half of the world’s languages. The 2007 investigation did not test whether genetics exerted any real-world effect on tone perception, however. “That study generated a hypothesis, but many people were pretty skeptical,” Wong says. “We really needed direct evidence.”
In the new study, Wong and his colleagues performed listening tests on more than 400 native Cantonese speakers to determine each participant’s proficiency at distinguishing the language’s six tones. They administered additional tests to measure the volunteers’ IQ, memory, and musical pitch and rhythm. The team genetically analyzed participants’ saliva for nine variants of three genes hypothesized to be connected to tone perception, as well as 13 variants of seven genes thought to play a role in general language processing.
The researchers’ analysis revealed that only a single variant of the ASPM gene known as TT—one of the two variants identified in the 2007 paper—predicted how well participants could perceive tone. They also found that the majority of the people they tested, about 70 percent, had the TT variant (which consists of two copies of the base thymine), confirming its prominence in the Cantonese-speaking population.
The gene’s overall effect, however, was still small: it ranked behind IQ and musical background in terms of predicting tonal proficiency. But applied over many years, subtle genetic differences can exert significant influence, Wong says. “It reveals a potential underlying mechanism of how language evolves.”
Damián Blasi, a language scientist at Harvard University, who was not involved in the study, agrees that small genetic effects could potentially drive language change. But he emphasizes that researchers still have much to learn. “I would not expect any single study to be a definitive demonstration of a causal effect in a language change,” Blasi says. “And this study is no exception.”
Wong’s paper, however, is still “a big step in the field because it uses a more suitable experimental design than previous work and a considerably larger sample size,” says Balthasar Bickel, a linguist at the University of Zurich, who also was not involved in the research. The study also highlights the need for “far tighter collaboration between biologists and linguists than what happens traditionally,” he says.
Wong hopes to carry out follow-up studies with speakers of other tonal languages in Southeast Asia, China and Africa. He also plans to explore the practical implications of the findings.
Speech disorders, for example, often cause problems with pitch perception for speakers of tonal languages, so clinicians could potentially use ASPM, along with other genes, in early genetic screenings to identify children at risk of such disorders. The fact that ASPM seems to be tied to tonal perception also implies that any genetic test used to screen for speech impairments should be tailored to specific populations, depending on the language spoken. “There’s no one-size-fits-all solution,” Wong says.
The new study also hints at possible interventions for certain speech and language disorders. Unexpectedly, Wong and his colleagues’ analysis reveals that musical training of any kind—including something as simple as childhood piano lessons—increased tonal perception in participants who did not carry ASPM’s TT variant. Violin or voice lessons could be an early intervention for those who speak a tonal language and are at risk for a language impairment, Wong says. They may include autistic tonal language speakers, who sometimes struggle with pitch perception.
“Genetic testing is not just about testing. It’s about planning for interventions,” Wong says. “To me, the possibility of interventions for helping at-risk groups is the most exciting aspect of this.”