language

Nicholas Wade today covers a new study by Wolfgang Enard and colleagues, in which they generated transgenic mice expressing the human-derived version of FOXP2.

Naturally, the mice squeak differently.

In a region of the brain called the basal ganglia, known in people to be involved in language, the humanized mice grew nerve cells that had a more complex structure and produced less dopamine, a chemical that transmits signals from one neuron to another. Baby mice utter ultrasonic whistles when removed from their mothers. The humanized baby mice, when isolated, made whistles that had a slightly lower pitch, among other differences, Dr. Enard says. Discovering that humanized mice whistle differently may seem a long way from understanding how language evolved. Dr. Enard argues that putting significant human genes into mice is the only feasible way of exploring the essential differences between people and chimps, our closest living relatives.

Interestingly, the human version fills in "perfectly for the mouse version in all the mouse’s tissues except for the brain." Well, I suppose that is to say that there are no measured changes in other tissues where FOXP2 is expressed.

I pointed to a study of FOXP2 knockout mice in 2005, and that study is mentioned here as well.

Meanwhile, if you want to hear mice squeak, the Times includes an audio file. Oh, and the Stuart Little element:

“People shouldn’t think of this as the one language gene but as part of broader cascade of genes,” [Gary Marcus] said. “It would have been truly spectacular if they had wound up with a talking mouse.”

I'm doing a little literature review this week on Middle Pleisocene postcrania. On a somewhat tangential topic, the description of the Sima de los Huesos cervical vertebrae, by Gómez-Olivencia and colleagues (2007), includes a nice summary of the current knowledge of the thoracic vertebral canal of KNM-WT 15000 and other early Homo specimens.

Much attention has been devoted to vertebral-canal size and its relationship to spoken language. One factor in the evolution of human language that would be reflected in vertebral-canal morphology is increased breath control (MacLarnon, 1993, MacLarnon and Hewitt, 2004). Modern humans have an enlarged thoracic vertebral canal, reflecting a larger amount of gray matter. Based on the morphology of the KNM-WT 15000 individual, a narrower thoracic canal has been proposed for Homo ergaster, indicating that this species may only have been capable of short, unmodulated utterances, such as those used by extant nonhuman primates (MacLarnon and Hewitt, 1999). However, significant abnormalities have been found in the KNM-WT 15000 individual (Latimer and Ohman, 2001), which could indicate some form of axial dysplasia, and so the small canal may be a reflection of a neural-canal stenosis associated with the pathology. In contrast, Schiess et al. (2006) argued that the diagnosis of a congenital dysplasia is not supported, indicating that the pathological lesions in the KNM-WT 15000 individual may not be as severe as previously reported. Moreover, the Dmanisi vertebrae (Meyer, 2005 and Meyer et al., 2006), which are the oldest known for the genus Homo, follow the modern human pattern in all regions, as the raw and relative sizes of the vertebral canals fall well within the human range, indicating that these hominins may have had fine control of the respiratory muscles involved in spoken language (Meyer, 2005 and Meyer et al., 2006).

Arsuaga et al. (1997a) showed that the mean cranial capacity of SH's three most complete crania (1245 cm³) (Arsuaga et al., 1993 and Arsuaga et al., 1997c) is slightly less than that of two comparative samples from the Hamann-Todd Osteological Collection. However, given the large body-weight estimates for these hominins, their encephalization quotients are below both modern human or Neandertal values (Arsuaga et al., 1999). In Neandertals, higher encephalization quotients are reached by expansion of the cranial capacity, while in modern humans it is mainly achieved by a reduction in body mass (Arsuaga et al., 1999 and Carretero et al., 2004). In addition to the parallel trends in encephalization in these two lineages, the absolute size of the bony vertebral canal in the upper cervical spine reached modern human values by the middle Pleistocene. Preliminary studies (Carretero et al., 1999, Gómez et al., 2004 and Gómez-Olivencia, 2005) have shown that the SH lower cervical spine's canal had a similar size compared to modern humans, but a full assessment of this anatomical region will not be possible until larger sets of cervical and thoracic vertebrae are associated. In any case, as demonstrated by Martínez et al. (2004), the SH hominins had the skeletal characteristics of the outer and middle ear that support the perception of spoken language (Gómez-Olivencia et al. 2007:22).

The Meyer references are to Marc Meyer's dissertation on the Dmanisi vertebral remains and a subsequent conference presentation. I think those are more than sufficient to say that this particular piece of anatomy isn't evidence for restricted breathing control in early Homo. I don't have much more to say, just though these two paragraphs sum up a lot of information in a useful way.

References:

Gómez-Olivencia A, Carretero JM, Arsuaga JL, Rodríguez-García L, García-González R, Martínez I. 2007. Metric and morphological study of the upper cervical spine from the Sima de los Huesos site (Sierra de Atapuerca, Burgos, Spain). J Hum Evol 53:6-25. doi:10.1016/j.jhevol.2006.12.006

How are languages and genes related to each other? Anthropology is an interdiscipinary subject, and this is probably the topic that pushes that envelope the furthest, in terms of calling on the expertise of many different disciplines in the humanities and sciences.

As an organizing principle, many workers have begun with the hypothesis that languages and genes each form genealogical relationships among populations, and that the coevolution of languages and populations should make these genealogies resemble each other. In other words, French, Spanish, Portuguese and Italian all descend from Latin, and the present-day populations of France, Spain, Portugal, and Italy all descend from the population of the Roman Empire. Hence, the relations of the languages and the relations of the populations are parallel to each other.

This general idea is older than Darwin’s Origin of Species, but Darwin’s words on the subject have been quoted more often than anyone else’s:

Like many of Darwin’s words, however, these are generally pulled from the surrounding context without further discussion. The sentence actually serves as an example in Darwin’s defense of the phylogenetic tree as a description of relationships. In the previous paragraph, he points out that the similarities among different species cannot be made to fit any simple series. Instead, a hierarchical, genealogical arrangement can account for many of their similarities and differences. And after this sentence, he describes differences in rate of language change as an analogy for the evolution of organisms:

Thus, Darwin’s discussion—in which language relationships are an example—raises two separate issues: (1) Whether similarities are described by seriation or hierarchy, and (2) Whether differences arise at a constant or changing rate. His readers would have been aware of historical linguistics, including the observation that no ”Great Chain” of languages could be constructed out of grammatical and phonological changes that are manifestly hierarchical. Likewise, they would be familiar with two ancient languages that had manifested long-term stasis in a small community of speakers.

These points discussed by Darwin remain active elements of debate about the relationships of recent human languages and genes:

• How much of linguistic diversity is attributable to the genealogical relations among languages, and how much derives from horizontal modes of transmission, such as the borrowing of words and syntactic patterns?
• How often do populations undergo language shifts?
• How much of human genetic variation is attributable to ancient population divergences, and how much to recent gene flow?
• Are genes today the same as those present in ancient populations, or have they been replaced by selection or other demographic processes?

Each point considers a way that the genealogy of languages may come to differ from genetic relationships of populations. Within a single generation, there is a very high concordance between language and genes: People inherit their genes from their parents, and they tend to learn the same language as their parents. But only a slight mismatch in each generation may, over the course of many generations, add up to a huge difference in the histories of the two systems. And if those differences are biased in some direction, instead of random noise, then they may not only obscure the real history; they may strongly point to a false one.

To return to our example: French, Spanish, Portuguese, and Italian are not the only major Romance languages: there is also Romanian, for example. Romanians are genetically most similar to their neighbors in southeastern Europe, such as Serbs and Greeks—neither Romance speakers. In this case, population movements after the Roman period, such as the migrations of Slavic peoples, transformed the languages spoken in the Balkans without fundamentally altering the genetic similarities. And the persistence of Greek reminds us that the vast expansion of the Roman empire could not supplant some linguistic communities, and did not itself erase some earlier genetic patterns.

So should we expect the ”perfect pedigree” of human populations to resemble the genealogy of languages? It would help if there were factors that tended to reinforce such similarities instead of destroying them. We have to go beyond the simple statistical comparison of language and gene trees, which over enough time really shouldn’t resemble each other very much—at least, if the deviations in their evolutionary patterns are just noise. Instead, we have to consider how demography shapes genetic and linguistic transfer.

References