FOXP2 and Language Evolution
In the early 1990s, a team of doctors from the Child Health Institute in London were finding themselves baffled by a group of patients with a severe language and speech disorder. The mysterious disorder affected about half of the members of a three-generation span of a single London family who would later be identified in the medical literature as the KE Family.
KE family members who had the disorder had both physical and cognitive impairments that affected their ability to communicate. This included difficulty performing fine motor movements of the face and mouth necessary for speech, inability to answer simple word problems, difficulty understanding complex sentence structure, and reduced IQ scores on both verbal and non-verbal tests.
In 1996, the physicians brought the case to the Wellcome Trust Centre for Human Genetics in Oxford, where a team led by geneticist Dr. Simon Fisher. Given the generational nature of the disorder, Fisher's team suspected that the cause was a single-gene mutation somewhere on chromosome 7, but narrowing down exactly which gene was responsible was a difficult problem.
The solution came as a stroke of luck - an entirely unrelated patient nicknamed CS was presented to the team displaying similar language and cognitive difficulties. In this patient, a portion of chromosome 7 had been broken off and spliced onto a different chromosome. The break occurred in the middle of a gene known as FOXP2. Sequencing of this gene in the KE family found a point mutation - a DNA copying error substituting one nucleotide for another - in affected members of the family. A single guanine (G) had been replaced with adenine (A) in a critical part of the gene, causing the gene to code for one wrong amino acid in the protein produced.
This single mutation created both physical and mental impairments to language ability in the KE family, and a break in this gene had caused similar impairments in the patient CS. The conclusion was that the FOXP2 gene was extremely important to language development.
The Molecular Evolution of FOXP2
FOXP2 is named for the Forkhead Box Protein P2 for which it codes. This highly complex protein, which gets its name from its forked appearance, is a type of protein known as a transcription factor. Transcription factors act as facilitators, enabling the DNA of other genes to make RNA, and thus make other proteins to perform functions for the organism. In other words, forkhead proteins are regulators that turn genes on or off, a process known as gene expression.
Though FOXP2 was widely described in the popular press as a "language gene" and in some cases presented as "uniquely human," it is in fact a very old gene. Very similar versions of FOXP2 are found not only in other mammals such as chimpanzees, mice, and bats, but it is also found in birds, fruit flies, and even single-celled organisms such as yeast. During embryonic development in humans and other mammals, FOXP2 regulates formation of the brain, esophagus, lungs, heart, and several other internal organs.
Later in life, the gene continues to enable development of language and communication pathways. This has been demonstrated by experiments using zebra finches - a type of songbird that learns new songs every year and modifies their songs during the mating season. When the birds were injected with RNA that inhibited the function of FOXP2, they had difficulty learning and remembering new songs, and their songs came out garbled and off-key.
Comparisons of the gene sequence in different modern organisms demonstrates that it has undergone very little change throughout its evolutionary history. In genetics, this is referred to as being highly conserved. In the 75 million years since the mammal lines that became mice and humans diverged, the gene sequence has changed by only three amino acids. Two of these happened very recently - just in the five million years since the human and chimpanzee lines diverged.
Interestingly, one of the amino acid changes that occurred after the human-chimpanzee split also happened in echolocating bats, suggesting that human language and bat echolocation are controlled by similar gene regulation pathways. An even more interesting finding is that the Neanderthal genome contains a version of FOXP2 identical to that found in modern humans, suggesting that Neanderthals may have been capable of complex language.
Sources and Further Information
- FOXP2 and the Evolution of Language
This article addresses the history and the significance of the discovery of the relevance of FOXP2 in the development of speech. It is a remarkable scientific detective story that has been in the making for some time.
- Foxp2 Mutations Impair Auditory-Motor Association Learning
Simone Kurt, Simon E. Fisher, Gunter Ehret - PLoS ONE. March 2012, Volume 7, Issue 3.
- Wellcome Trust Centre for Human Genetics - Research Projects
The laboratory pioneers new ways of uncovering brain pathways that are important for speech and language development, approaching this fascinating question from a unique perspective.
- The FOXP2 story: A tale of genes, language and human origins | The Human Genome
A single family with speech abnormalities may hold one of the keys to the origin of human culture.
- Revisiting FOXP2 and the origins of language : Not Exactly Rocket Science
This is an updated version of a feature I wrote on FOXP2 (the so-called "language gene" for New Scientist, now edited for 2009 to include breaking research.