Scientists have long struggled to understand how human language evolved. Words and sentences do not leave fossils behind for paleontologists to excavate.
Genetic research published Tuesday provides important new clues. Researchers discovered that between 250,000 and 500,000 years ago, a gene known as NOVA1 undergoes significant evolutionary changes in our ancestors. When scientists put the human version of NOVA1 in the mouse, the animals produced more complex sounds.
Erich Jarvis, a neuroscientist at Rockefeller University and co-author of the new study, warned that NOVA1 alone did not suddenly switch language skills from their ancestors.
“I'm not saying it's a language gene,” Dr. Jarvis said.
Instead, language has emerged over millions of years thanks to mutations in hundreds of genes.
“But where does nova1 fit all of that combination? This is one of the last steps,” Dr. Jarvis said.
Nova1 attracted scientific attention in 2012, when it appeared on a special list of genes that produce proteins that are identical in most mammals but have different forms in humans. Of the over 20,000 protein-coding genes, only 23 made a list. Everything was probably essential to the evolution of our species.
Nova1's list surprised Dr. Robert Darnell, a neuroscientist at Rockefeller University, who discovered the gene in 1993. He was surprised that genes appear to be essential for all mammals. A mouse designed without NOVA1 will die during development. Dr. Darnell's work did not suggest that genes played a distinctive role in human evolution.
Dr. Darnell began to learn more by working with evolutionary biologists. One of them, Adam Siepel of Cold Spring Harbor Laboratories in New York, led an effort to reconstruct genetic history. He saw the sequence of genes in extinct human DNA and genetic information from over 650,000 living people.
Dr. Siepel discovered that NOVA1 caused dramatic changes shortly after their ancestors split from Neanderthals and Denisovan, offering evolutionary benefits to early humans who inherited the change. In the end, it overwhelmed the original version of Nova1.
Since then, Dr. Siepel said that versions of the gene remained overwhelmingly dominant in the population. Mutations that reverse Nova1 to its original form are extremely rare and must be harmful. Of the 650,000 people registered in the database, only six carried the original version of the gene.
Researchers know nothing about who these six are. Dr. Darnell is currently searching for his original NOVA1 career, hoping to test his speech skills.
In the meantime, Dr. Darnell and his colleagues designed mice carrying human versions of nova1, not found in other mammals. On all appearances, the NOVA1 mice looked normal. But they had some differences.
The human version of Nova1 oversaw the production of 200 proteins in the mouse brain, where the normal version of the gene was not. And many of these proteins played a role in how animals produce sound.
“To me, it was like 'bingo!',” Dr. Darnell said.
If Nova1 shapes the evolution of human language, Dr. Darnell infers, and that human version may change the way the mouse produces sounds. Dr. Jarvis, an expert in animal vocalization, helped Dr. Darnell steal the animals.
Mice usually produce ultrasound creak pulses similar to human language syllables.
However, the mouse carrying the human version of Nova1 had a distinctive creak, scientists found. The difference was particularly noticeable when men sang courtship songs to women. Their songs contained more complex sounds, and the mouse switched those sounds in more complex patterns.
An interesting change in the evolution of Nova1 occurred after their ancestors split from Neanderthals and Denisovan. However, another linguistic gene known as FOXP2 received a burst of significant changes prior to its division. And research has shown that mice carrying the human FOXP2 gene also produce strange creaks.
Some scientists have speculated that the two genes independently altered both human brain regions that produce complex sounds.
“The exciting thing about Nova1 is that there's another child on the block,” said Wolfgang Enard, a geneticist at Ludwig Maximilian University who worked on FOXP2 mice.
Dr. Jarvis said he believes that the common ancestors of modern humans, Neanderthals and Denisovan can speak, perhaps thanks to genes such as FOXP2. However, mutations to other genes, including NOVA1, could have given only modern humans the ability to produce a wider range of complex sounds and expand the power of language.
To test that hypothesis, Dr. Jarvis hopes to engineer mice with mutations in NOVA1, FOXP2, and other genes that may be important in language elevation. Together, these mutations can cause mice to generate even more complicated calls.
