Although animals have the ability to communicate, the capacity for complex speech and language skills is exclusively human. Scientists have long puzzled over the origins of this amazing human ability to organize vocal sounds into words and words into meaningful sentences. Within the past decade or so, molecular biologists have begun to identify genes linked to speech and language. These findings are helping to decode the evolutionary and neurological enigma of human language. They are also offering possible explanations for how autism and other language-related disorders develop.
Researchers have predicted the structure of the FOXP2 protein, which is important in speech and language. The illustrated portion of the protein binds to and controls genetic information within cells. The red mark shows the position of a mutation in FOXP2 that causes severe speech and language deficits.
In 1996, a British family with a multi-generational history of severe language and speech problems was referred to a team of geneticists in Oxford. Such problems often run in families, but this particular family was unusual. Half its members had a rare disorder that made it difficult to master the sequences of fine mouth movements necessary to speak clearly. They also had difficulties with both spoken and written language, including problems with spelling and grammar.
Due to the large percentage of family members affected and the pattern in which the disorder was passed on from one generation to the next, the geneticists suspected that it was the result of a defect in a single gene. Armed with the new tools of molecular genetics, they painstakingly tracked the gene defect to a region of chromosome 7. From the 70 or so genes contained there, the geneticists eventually identified the single mutation on the single gene — now called FOXP2 — responsible for the family’s symptoms.
This remarkable discovery, reported in 2001, marked the first time a single gene had been directly linked to language and speech. Since then, scientists have not only identified additional cases of FOXP2 mutation, but have also begun to uncover other genes that are important in human communication. This research is leading to:
- A greater understanding of the neural pathways that underlie speech and language, offering potential targets for the treatment of speech and communication disorders.
- An insight into the evolutionary origins of speech and language.
FOXP2 is not the gene that makes language happen; it’s unlikely that any single gene exists solely to enable us to communicate. But genes like FOXP2 interact with other genes in complex ways to build a language-ready brain. FOXP2 could have a leading role in this process because it is a transcription factor — a protein that binds to and controls genetic information within cells. Scientists believe the FOXP2 protein may help other genes express themselves in the developing human brain in ways that ensure the learning of speech and language skills.
A defective copy of FOXP2, therefore, can alter the way the brain handles language. Indeed, sophisticated brain imaging studies have shown that when people with a faulty FOXP2 are involved in language tasks, they exhibit below-normal activity in the Broca’s area, a brain region essential for speech production and language processing.
FOXP2 has changed little throughout vertebrate evolution; the versions found in other species are only slightly different than those found in humans. In animals, as in humans, defects in the gene can lead to communication problems. For example, if FOXP2 is silenced in the brains of young zebra finches, they go on to produce garbled, incomplete songs. When the gene is completely inactivated in baby mice, they have difficulty making their high-pitched squeaks.
Chimpanzees — our closest evolutionary relative — have a version of FOXP2 that differs very little from that of humans. Yet that difference could be critical and may have contributed to our far more sophisticated language skills. Scientists aren’t sure when the human FOXP2 took its current form. Initial evidence suggested it happened within the past 200,000 years—consistent with the time when humans were expanding their populations and emerging from Africa.
Yet the modern human version of FOXP2 may actually have been around much longer. It’s been found in the DNA of Neanderthal fossils, and the split between Neanderthals and humans is believed to have occurred around 350,000 years ago. Although a single gene is not enough by itself to tell us whether or not an extinct species could speak, this finding raises the provocative possibility that Neanderthals may have had some form of rudimentary language skills.
Language-related genes may be at the very core of disorders like autism that affect language acquisition and social communication. In recent years, researchers have identified several dozen brain-related genes potentially regulated by FOXP2. One of these genes, CNTNAP2, is associated with autism and other common forms of language-impairment.
So much about language and genes is yet to be discovered, including the intricate pathways by which these genes interact. Thanks to new advances in molecular genetics and neuroscience, scientists are beginning to unlock the neurological mystery of what makes human language so unique in the natural world and help those who suffer from speech and communication disorders.