Surprising news from China finds extensive indications of evolution in the so-called language gene, FOXP2, among bats that use echolocation to find prey on the wing. The FOXP2 gene was first identified as an object of special interest when it was found that a family with a hereditary speech disorder had a mutated FOXP2 gene. Further examination of this gene found that it was unusually stable. Mice, gorillas, and chimpanzees have almost identical FOXP2 genes, while the human FOXP2 gene differs from the chimpanzee’s by two adaptive amino acids. A further exploration found that rabbit, marmoset, armadillo, baboon, and orang utan FOXP2 genes are very stable. This kind of stability argues that the gene is already optimal and allows for very little drift. A team led by Gang Li of the East China Normal University in Shanghai has a new paper available online from PloS One (here) that reports their discovery about bat FOXP2 structure in considerable detail. Bats may seem an unlikely source for any insight into speech, but the paper makes a strong argument against that prejudice. Bats are great vocalizers and, like humans, must attend to very brief differences in sounds if they are to understand the meaning of what they hear.
The difference in the spoken sounds of bus and buzz passes in milliseconds, so fast that adult humans whose own language does not use ss and zz to distinguish between words are hard put to hear the difference and even harder pressed to voice the distinction themselves. The easy way people with normal hearing and speech catch and make these sounds is a remarkable feat, one that is not found anywhere else in the primate line or among most other mammals. It is, however, duplicated—and then some—among echolocating bats.
These animals can make up to about 200 sounds per second, interpret the echo, and respond appropriately, all within milliseconds, as they catch small insects flying through the darkness. Imagined as speech, echolocation is a monologue in which the flying bat is both speaker and listener. What could be more mechanical, I have always assumed, than the emission of echolocating sounds? But it turns out that there is much information in the tones emitted and bats can change their sounds in response to what they hear. It is a great feat of sensorimotor coordination.
Studies with mice have shown that terrible results follow if you disrupt the FOXP2 gene’s workings, including an absence of the ultrasonic vocalizations that mice pups usually make when they become separated from their mothers. (Abstract here) The authors of the echolating-bats paper assert that it has become generally accepted that the gene “functions in sensorimotor coordination.” This research suggests that the FOXP2 gene is not a language gene in the sense people normally imagine, something that governs syntactic, meaningful, or symbolic thinking. On the other hand, speech may be much more of a physical achievement than we have generally realized.
Bats are a very old type of mammal. Gang Li’s team reports that they began to diverge from other mammals around 80 million years ago, which is before the dinosaurs disappeared. Echolocation is apparently a very old part of the bat’s repertoire of oddities and their FOXP2 genes have strayed much further from the standard rodent version of the gene than humans have wandered. They have also strayed in a different direction, so to speak, from humans, changing different amino acids. Thus, although we can say that echolocating bats have seen an unusually extensive series of changes in the FOXP2 gene, they do not resemble the changes humans show. The authors do not know for sure what to make of this extensive evolution, although they speculate that the “protein [created by the gene] might function in the mobilization of downstream genes (or genetic cascades) involved in one or more aspects of the development or regulation of complex sensorimotor coordination.” [p. 6]
Speaking technically, the gene is a transcription factor, meaning it controls the operation of many other genes. Thus, although FOXP2 is a single gene, it is implicated in the construction of many proteins so its effects can be widespread and various. It is likely to be some time before we understand its effects in detail, although it appears to be important for precise articulation and, perhaps, vocal learning.
I’m going to keep my eye out, however, for further information on what comes with clear diction. One thing that seems possible is that we can speak longer sentences. Wouldn’t it be funny if the transition from a pidgin-like protolanguage of short sentences to modern sentence structure came, not from some mutation that gave us syntax or the power to think recursively or the capacity to think symbolically, but the ability to utter long strings of intelligible sounds!