A new study from the University of Iowa Health Care suggests that a surprisingly small portion of human DNA plays a major role in language ability. The researchers also discovered that these influential gene sequences appeared before modern humans and Neanderthals diverged from a common ancestor, pushing the origins of language-related biology further back than previously realized.
Language is one of the defining characteristics of Homo sapiens, says Dr. Jacob Michelson, the Roy J. Carver Professor of Psychiatry and Neuroscience at the UI Roy J. Carver and Lucille A. Carver School of Medicine. Many animals communicate, but humans have a remarkable ability to create, adapt, and extend language in ways that no other species does.
Michelson and his colleagues, including lead author Dr. Lukas Kasten, now a postdoctoral fellow at the Max Planck Institute for Psychiatry in Munich, Germany, set out to investigate how human language development may have been influenced by genetic regulatory elements known as hominid ancestral rapidly evolving regions (HAQER).
“What we’re seeing is how a small part of the genome can have such a huge impact not just on us as a species, but on us as individuals,” Michelson said, noting that HAQER is less than one-tenth of the genome, but it has about 200 times more impact on language ability than any other region of the genome.
According to the researchers, these regions of DNA help build the brain’s biological “hardware,” and language itself acts as the “software.”
Ancient DNA and the origins of language
The survey results are scientific progressbased on research begun in the 1990s. At the time, Dr. Bruce Tomblin, now professor emeritus in the UI Department of Communication Sciences and Disorders, studied the language skills of 350 students in Iowa.
Tomblin carefully recorded each student’s language skills and collected saliva samples to preserve DNA for future analysis. A few years later, Michelson’s lab completed gene sequencing through NIH-funded research, making it possible to examine how differences in DNA are related to differences in language ability.
As the researchers examined the data, they became interested in HAQER’s broader role in human communication.
“We’re not talking about genes; we’re talking about regulatory regions that act like volume knobs for genes,” Professor Michelson explains, adding that the discovery quickly connects with seminal work more than 20 years ago that identified the FOXP2 gene, a transcription factor that was initially suspected to play a key role in language disorders. “So if HAQER is like a volume knob that you can turn, FOXP2 is one of the hands that is turning those volume knobs.”
To better measure the impact of HAQER, researchers created the Evolutionary Stratified Polygenic Score (ES-PGS). This is a tool that separates genetic effects according to when they appeared during evolution. The research team used computational genetics to track genetic influences over about 65 million years of evolutionary history.
Common genetic characteristics with Neanderthals
The analysis revealed that these genetic “volume knobs” were already present in Neanderthals and may have been slightly more pronounced than in modern humans.
For researchers, this was a particularly important discovery because it suggests that HAQER is an ancient biological innovation related to language. The link exists even though Neanderthals may have differed greatly from modern humans in many aspects of cognition.
“This aspect of HAQER, which is part of the genome, remains relatively constant, even though other aspects are increasingly improving to make modern humans increasingly smarter,” Michelson says. “We can say that humans at least had the ‘hardware’ for language earlier than previously thought.”
Michelson points out that archaeological evidence already shows that Neanderthals had a culture, social organization, and complex behavior. Combined with new genetic discoveries, these observations strongly suggest that some form of advanced communication may have existed long before modern humans emerged.
This result also raises important questions. If HAQER is so beneficial to the language, why has it stopped changing instead of continuing to evolve?
evolutionary trade-offs
Researchers think the answer involves a process known as balancing selection.
While genetic signals associated with other cognitive abilities continue to evolve, the impact of HAQER appears to have plateaued. The researchers say these gene regions support fetal brain development by also increasing the size of the brain and skull.
But before modern medicine, there was a limit to how large an infant’s head could get before childbirth became dangerously difficult for both mother and baby. Increasing head size can significantly increase the risk of death during childbirth.
“Early humans likely took full advantage of this pathway to develop the kind of brain that could be a vessel for language, reaching its upper limit fairly early on and remaining stable thereafter, while other aspects of genetics that improve brain development for higher intelligence but do not directly influence fetal brain size continued to evolve,” Michelson says.
In other words, human evolution may have reached a point where further improvements in the biological “hardware” that supports language would come at too great a cost to the survival of mother and child.
Separating genetics from environment
The team plans to continue investigating these questions using the same group of participants that Tomblin originally studied.
Because this study began nearly 30 years ago, many of the participants now have children and families. This creates a valuable opportunity to investigate how language ability is shaped by both genetics and environmental influences.
“One of the things we’re interested in when thinking about how children acquire language is disentangling environmental input and genetic input,” Michelson says, noting that children who grow up in linguistically rich environments may show higher language abilities. “We hope to use that family structure to separate direct genetic influences on language from what researchers call ‘genetic nurture,’ where a parent’s genetics influences the environment they create for their child.”
Michelson said the University of Iowa has advanced statistical tools that could help researchers distinguish between environmental and genetic influences on language learning. Such insights could lead to important clinical applications.
To advance that research, Michelson and Kristy Hendrickson, Ph.D., associate professor of communication sciences and disorders, submitted a grant proposal to support the next phase of research.
In addition to Michelson, Kasten, and Tomblin, the research team included current and former UI researchers Dabney Hoffaman, Savantha Thenuwala, Alison Momany, Marlea O’Brien, Jeffrey C. Murray, and Tanner Coomer (now at Recursion Pharmaceuticals). Taylor R. Thomas of the Massachusetts General Hospital Genome Research Center and Jinyoung Ko of the University of Maryland also contributed to the study.
The study was funded in part by a grant from the National Institute on Deafness and Other Communication Disorders, part of the National Institutes of Health, and the National Institute of General Medicine, and the Roy J. Carver Charitable Trust.
