Tag Archives: genetics

Should Mother Tongue be Father Tongue?

A new paper, published in Science last week, has reviewed some of the correlations which suggest that language change may be subject to sex-specific transmission. This has been discovered through looking at Y-chromosome DNA types. Modern male DNA (Y-Chromosome) is found to be the DNA from the population who originally spoke the language which has survived, whereas modern female DNA is often not the DNA of the population which spoke the language which has survived.

This evidence has come from, among others, a study by Chaubey (2011) with evidence for the Indian subcontinent. Austroasiatic languages are spoken by tribes with a high proportion of immigrant Y-chromosome DNA from East Asia, but with a high percentage of local female (mitochondrial) DNA. This pattern was also true of the Tibeto-Burman language family in northeastern India.

Other studies found matching correlations in Africa and found that Niger-Congo languages correlate with Y-Chromosome types, but the female DNA, which correlated more with geography (Wood et al. (2005) and de Filippo et al. (2011)).

Sex-biased language change can also be seen in the expansion of the Malayo-Polynesians in New Guinea. New Guinea has populations of Malayo-Polynesian speakers and also populations of Melanesian speakers. Malayo-Polynesian female DNA is about the same in both Malayo-Polynesian speaking areas and Melanesian speaking areas. However, the Malayo-Polynesian Y-Chromosome is found way more in the Malayo-Polynesian speaking areas than the Melanesian speaking areas.

This pattern is also seen in Iceland where the female DNA is mainly British, but the Y-chromosome is mainly Scandinavian. This follows the pattern because the Icelandic language is also Scandinavian.

Forster and Renfrew (authors of the Science paper) show that these findings complement studies such as Stoneking and Delfin who found that in East Asia, it is women who move after marriage rather than men. This means that if a man and woman migrate to a populated area their female offspring will move to other villages when married but their male offspring will remain static meaning that their language will stay in the same place as their Y-Chromosomes.

Is this the only mechanism at work when correlations of sex-specific language change can be seen? Others have hypothesized things such as farming and trade might be a factor. Groups of emigrating agriculturalists may also contribute where men outnumber women and take wives from the local community they were moving to. Men are also biologically capable of passing on and spreading about much more of their DNA than women can. It may also be the case that it is the father’s language rather than the mother’s which will be dominant within a family but I think more research would have to be done on this.

Interestingly the opposite correlation to the ones seen above is seen in Greenland where both the language and female DNA is Eskimo but the Y-Chromosome DNA is European.

Neanderthal-human Hybrids

Paul Mason and Robert Short have an article out called Neanderthal-human hybrids (I wonder what that’s about?). Here is the abstract:

Evidence from studies of nuclear and mitochondrial DNA extracted from Neanderthal fossils and humans points to fascinating hypotheses concerning the types of interbreeding that occurred between these two species. Humans and Neanderthals share a small percentage of nuclear DNA. However, humans and Neanderthals do not possess the same mito­chondrial DNA. In mammals, mitochondrial DNA is exclusively maternally inherited. Taking into account an understanding of interspecific hybridity, the available data leads to the hypothesis that only male Neanderthals were able to mate with female humans. If Haldane’s Law applied to the progeny of Neanderthals and humans, then female hybrids would survive, but male hybrids would be absent, rare, or sterile. Interbreeding between male Neanderthals and female humans, as the only possible scenario, accounts for the presence of Neanderthal nuclear DNA, the scarcity of Neanderthal Y-linked genes, and the lack of mitochondrial DNA in modern human populations.

Paul Mason previously wrote about the topic over at Neuroanthroplogy, so I really don’t have much more to say on the topic, other than that I’ll get around to reading it over the next couple of days. I’m curious to see if the usual suspects in the genetics (Razib Khan), anthropological (Dienekes) and evolutionary (John Hawks) communities offer some food for thought on the topic.

For me, I’m actually more interested in Mason’s recent work on degeneracyBut that’s for a later post ;-)

Out of (Southern??) Africa

It is a largely unchallenged claim of anthropologists that the human race emerged from the continent of Africa. However, claims relating to our evolution before our nomadic ancestors left the land of our origin have been left largely abstruse.

A new paper published on PNAS.org this week attempts to address this very problem through genetic analysis of several hunter gatherer societies in Africa including speakers of the nearly distinct N|u language. This was done because hunter-gather populations remain divergent in their variations at a level which is no longer maintained in the African population as a whole.

580,000 Single-nucleotide polymorphisms (SNPs) were analysed to calculate genetic relationships and diversity between the groups and propose possible evolutionary paths and branches.

Henn et al. (2011) propose that the genetics of those groups found in the south of Africa are the most diverse, and therefore the oldest, of any diversity found among other modern humans. This has caused them to suggest that the origins of modern humans may in fact be in southern Africa as opposed to the much more accepted view which is that we emerged from the east of Africa.

This assumed eastern viewpoint is a result of the earliest modern human skulls being found in the east and also the fact that humans in the rest of the world all carry a subset of genes found specifically in eastern Africa. However, until now, the populations represented in the study by Henn et al. (2011) have not been represented in previous genetic studies when making estimates of the whereabouts of our evolutionary origins.

Some dispute has arisen regarding these conclusions because the current whereabouts of these hunter-gatherer populations within Africa is not evidence to suggest that this is always where these populations have resided. These groups may have moved about and migrated from their original place of origin just as the rest of humanity has. Henn has retorted that, though this is a possibility, typically only a subset of a group moves to a new area, and this subset is less genetically diverse than the parent population. This would mean that if a group of humans left eastern African for southern Africa they would be expected to be less diverse in the population who moved and this contradicts the genetic data found in Henn et al. (2011).

References

Henn, B. et al. (2011) Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1017511108

New Language and Genetics department

Next week, on the 1st October, there will be a new language and genetics department opening at the Max Planck Institute, the first research department in the world entirely devoted to understanding the relationship between language and genes!!!

This excites me so I wanted to share the news.

This statement is from Simon Fisher, who will head the new department about what they will be trying to achieve:

‘We aim to uncover the DNA variations which ultimately affect different facets of our communicative abilities, not only in children with language-related disorders but also in the general population, and even through to people with exceptional linguistic skills’, says L&G director Simon Fisher. ‘Our work attempts to bridge the gaps between genes, brains, speech and language, by integrating molecular findings with data from other levels of analysis, particularly cell biology and neuro-imaging. In addition, we hope to trace the evolutionary history and worldwide diversity of the key genes, which may shed new light on language origins.’

More signs of the growing and diversifying field of language evolution!

Here’s a link to the news on the MPI website: http://www.mpi.nl/news/new-mpi-department-language-genetics

Genetic Anchoring, Tone and Stable Characteristics of Language

In 2007, Dan Dediu and Bob Ladd published a paper claiming there was a non-spurious link between the non-derived alleles of ASPM and Microcephalin and tonal languages. The key idea emerging from this research is one where certain alleles may bias language acquisition or processing, subsequently shaping the development of a language within a population of learners. Therefore, investigating potential correlations between genetic markers and typological features may open up new avenues of thinking in linguistics, particularly in our understanding of the complex levels at which genetic and cognitive biases operate. Specifically, Dediu & Ladd refer to three necessary components underlying the proposed genetic influence on linguistic tone:

[...] from interindividual genetic differences to differences in brain structure and function, from these differences in brain structure and function to interindividual differences in language-related capacities, and, finally, to typological differences between languages.”

That the genetic makeup of a population can indirectly influence the trajectory of language change differs from previous hypotheses into genetics and linguistics. First, it is distinct from attempts to correlate genetic features of populations with language families (e.g. Cavalli-Sforza et al., 1994). And second, it differs from Pinker and Bloom’s (1990) assertions of genetic underpinnings leading to a language-specific cognitive module. Furthermore, the authors do not argue that languages act as a selective pressure on ASPM and Microcephalin, rather this bias is a selectively neutral byproduct. Since then, there have been numerous studies covering these alleles, with the initial claims (Evans et al., 2004) for positive selection being under dispute (Fuli Yu et al., 2007), as well as any claims for a direct relationship between dyslexia, specific language impairment, working memory, IQ, and head-size (Bates et al., 2008).

A new paper by Dediu (2010) delves further into this potential relationship between ASPM/MCPH1 and linguistic tone, by suggesting this typological feature is genetically anchored to the aforementioned alleles. Generally speaking, cultural and linguistic processes will proceed on shorter timescales when compared to genetic change; however, in tandem with other recent studies (see my post on Greenhill et al., 2010), some typological features might be more consistently stable than others. Reasons for this stability are broad and varied. For instance, word-use within a population is a good indicator of predicting rates of lexical evolution (Pagel et al., 2007). Genetic aspects, then, may also be a stabilising factor, with Dediu claiming linguistic tone is one such instance:

From a purely linguistic point of view, tone is just another aspect of language, and there is no a priori linguistic reason to expect that it would be very stable. However, if linguistic tone is indeed under genetic biasing, then it is expected that its dynamics would tend to correlate with that of the biasing genes. This, in turn, would result in tone being more resistant to ‘regular’ language change and more stable than other linguistic features.

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Where does the myth of a gene for things like intelligence come from?

As a linguist I struggle with genetics, I am, however, as an evolution geek, very interested in it. This creates all sorts of problems and high levels of anxiety when talking about FOXP2 and other genes, due to fear that I misunderstand the very highly complex interactions which exist between genes, environmental effects or cascading effects which cannot be summed up in a simple “x gene causes x trait in humans” paradigm.

I would like to point everyone towards a new blog Dorothy Bishop’s written over at guardian science blogs:

Where does the myth of a gene for things like intelligence come from?

Which is about busting the widespread belief (for idiots like me) that individual genes determine traits such as intelligence, optimism, obesity and dyslexia. I find it interesting that this is presented in the blogs section and not as a mainstream article.

She points out on Twitter this morning that the Jedward pic was not her idea. (I add this point because I found it weirdly comforting)

And it’s also lovely to see that at the bottom of the pile of comments is a well articulated reply by Dorothy to individual users.

I love blogging, because there exists  the ability for individuals to reply to claims made about them, primary sources (papers &c.) are cited and checkable and there’s none of the unnecessary dumbing down found in mainstream media. Here’s an article by Ben Goldacre expanding on this subject (which incidentally includes work by Dorothy Bishop).

Here is a parable about how, as a blogger, my claims were checked, discussed and ultimately concluded to be bollocks. (I don’t have a contrastive parable about what would have happened if I’d instead made these claims in the mainstream media but many stories of this nature can be found here.)

If you read the blog post I wrote about links between Autism and SLI you would have seen me make this claim:

the CNTNAP2 gene has been found in independent samples to be associated with both ASD and SLI. This is interesting because it could show that gene mutations which cause improved social abilities could have also caused changes in our linguistic ability on a syntactic or phonological level.

This blog post cited the work of Dorothy Bishop quite heavily and she took the time out to come and tell me problems with it. Here’s what she said:

As you anticipated, I think there are some problems with the implications you draw from the work. There are two issues. The first is that the variants of CNTNAP2 associated with language level are not mutations. You would usually only use that term in the case where most people had the same DNA sequence in a gene, but rare individuals had a different DNA sequence. FOXP2 is a case in point: there is a family, the KE family, who have a mutation affecting around half the family members, where the DNA sequence is changed. For most people in the general population, and for most people with SLI, the FOXP2 sequence is the same.

The CNTNAP gene is very different. The DNA sequence has different versions in different people, and one version, which is pretty common in the general population, is associated with a small decrease in language abilities, but most people with this version would not be recognised as having any language impairment. Most researchers now think that SLI is probably the result of the combined effect of many genes, each of which may nudge language ability up or down a bit. In this regard, language ability is rather like height: there are rare mutations that may make a person drastically tall or short, but most variation in height arises from combined effect of many small influences of genes that show DNA variation in the normal population.

The second issue concerns the evidence for CNTNAP2 being involved in both SLI and autism. Many people in the field do think this means that the same gene that can cause SLI can also cause autism, and that the only difference is that people with autism have additional difficulties going beyond language – what I have termed the ‘autism as SLI plus’ model. I supported that model in the past, but there are some facts that are hard to square with it. First, although many people with autism have structural language problems (affecting grammar and phonology) similar to those in SLI, not all of them do. So people with high-functioning autism or Asperger syndrome may have well-developed skills in syntax and phonology, while still having difficulties with pragmatics. The second point, which is a big problem for a simple genetic account, is that whereas the relatives of people with SLI often have some difficulties with structural language, we don’t usually see that in relatives of people with autism, even if the person with autism has poor language skills. It was this latter point that I was particularly keen to try and explain in my paper. The bottom line is that to explain the pattern of data we need to think in terms of interactions between genes (technically known as epistasis). So there are genetic variants that increase risk of autism, and others that increase risk of SLI. Most of these will have an individually small effect. However, if you have a risk variant for a gene influencing SLI (such as CNTNAP2) in the context of having a genetic risk for autism, the effect on language will be much worse. According to this model CNTNAP2 doesn’t affect both social cognition and language; rather it affects language, but that effect will get multiplied if the person also has risk factors for autism.

Which is SOOOO interesting.

I’d really like to thank her for replying, it’s really lovely to know that high-flying academics are willing to help out when a sincere blogger tries to understand something and falls on their arse.

Specific Language Impairment, Autism and Language Evolution

My last post speculated about what some conditions which manifest impaired theory of mind could tell us about the evolution of ToM. Of these conditions autism was one which could be the most informative when it comes to looking at the genetics of how ToM evolved, in this post I will look at what autism could tell us, not only about theory of mind, but also about other aspects of the language faculty.

Dorothy Bishop has recently written a paper exploring the above average co-occurrence of Specific Language Impariment (SLI) and Autistic Spectrum Disorders (ASD).

SLI is a condition where a child fails to develop spoken language on the normal schedule, for no observable or obvious reason (Bishop and Norbury 2008). Whilst ASD and SLI are regarded as distinct conditions, these disorders co-occur at above chance levels.

Bishop (2010) explores why this might be. Bishop begins her paper by painting a textbook example of a child with SLI. This example is of a child with normal social interaction and nonverbal communication, but with specific difficulties in mastering structural aspects of language, especially syntax and phonological skills. So this typical picture is not one of an autistic child in that one of the defining features of autism is a limited capacity for normal social interaction and a child is much more likely to be deficient in pragmatic skills than syntactic or phonological skills.

Bishop states that despite the fact that according to conventional diagnostic frameworks, SLI andASD are mutually exclusive diagnoses, similarities exist between the two conditions and these include:

  • They are both highly heritable
  • Identical, monozygotic twins are significantly more concordant than fraternal, dizygotic twins for autism and SLI
  • In both conditions rates of impairment in first degree relatives are higher than in the general population
  • First degree relatives of affected individuals of both conditions often manifest sub-threshold symptoms
  • These conditions correspond to points on a continuum of impairment, rather than all-or-none diseases

So any model of causation for either condition must take into account the following considerations:

  • Above chance levels of comorbidity between SLI and ASD
  • Rates of language impairment in relatives of probands with SLI and ASD
  • Molecular genetic findings of shared genetic risk factors for ASD and SLI

Now the article goes on to explore etiological models which explain these considerations with varying degrees of success. I’m not going to pretend to understand these models as I have only ever been formally taught in linguistics and so I’m a bit stumped by genetic psychology. If you’re much smarter than me you can read the article yourself here:

http://www.springerlink.com/content/gg087q4h51j5127g/fulltext.pdf

So what I got from this article was that the genetic factors involved in autism can not only cause the characteristics typical of a person with autism (pragmatic impairments) but also other language impairments which are typical of a person with a Specific Language Impairment. Specifically the CNTNAP2 gene has been found in independent samples to be associated with both ASD and SLI. This is interesting because it could show that gene mutations which cause improved social abilities could have also caused changes in our linguistic ability on a syntactic or phonological level.

Disclaimer: Sorry if I’ve made too many assumptions in the conclusion I’ve just drawn. As I said above I know next to nothing about genetic psychology but I just felt this research would have interesting consequences in the field of language evolution. I’d love to hear the thoughts of people who know better than I do.

References

Bishop, DVM. (2010) Overlaps Between Autism and Language Impairment:
Phenomimicry or Shared Etiology? Behavior Genetics 40:5, 618-629

Bishop DVM, Norbury CF (2008) Speech and language disorders. In: Rutter M, Bishop DVM, Pine D, Scott S, Stevenson J, Taylor E, Thapar A (eds) Rutter’s child

New Blog: Culture Evolves!

… Well, new to me at least. It’s run by Fiona Jordan of the Max Planck Institute for Psycholinguistics, and her latest post is an interview with one of my favourite researchers, Simon Greenhill (I didn’t know he designed a sudoku solving program). Also, after having done a little digging into her publications, I found the following forthcoming paper: The effect of population size and density on rates of linguistic evolution. Here is the abstract:

Evolutionary theory from population genetics predicts that demography may play an important role in determining the rate at which cultural and linguistic traits change over time. However, relatively few studies have explored this relationship for language at an appropriate scale and in a quantitative way, nor controlled for the problem of non-independence induced by the historical relationships between languages. Here we use phylogenetic trees of 351 Austronesian languages to test whether the rate of change in core vocabulary is affected by population size and population density. We detected a strong phylogenetic signal in both population size and density, indicating the need for historical control. We find a significant inverse relationship between lexical replacement and population size, no relationship with population density, and we confirm that splitting events influence lexical evolution. These results support the idea that a process analogous to genetic drift may be an important factor in lexical evolution. Furthermore, the strong phylogenetic signal in these demographic factors suggests that despite repeated population splits the social conditions that influence speech community size and density are maintained and inherited from one generation to the next.

I’m not going to say anything on a paper I haven’t yet read, other than it looks pretty cool and that more people should be considering the influence of demographic factors in linguistics.

Language – An Embarrassing Conundrum for the Evolutionist?

Hello! This is my first post on the blog and whilst I didn’t want it to be an angry rant after I found this youtube video there seemed little could have been done to avoid it.

This is a video by a creationist named “ppsimmons” who writes on the front page of his youtube channel that he “apologizes for not knowing enough to scientifically refute the evidence for creation nor for being clever enough to “scientifically” support the theory of evolution.” And yet he feels to be enough of an authority to make videos refuting evolution using ‘science’.

I know I shouldn’t let this annoy me as much as it obviously has, I know that there will always be creationists out there and I know that these creationists will never listen to anything I have to say. However, in this case, I’ve decided to respond mostly to set straight the interpretation of Robert Berwick’s words used in this video.

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Words as alleles: A null-model for language evolution?

ResearchBlogging.orgFor me, recent computational accounts of language evolution provide a compelling rationale that cultural, as opposed to biological, evolution is fundamental in understanding the design features of language. The basis for this rests on the simple notion of language being not only a conveyor of cultural information, but also a socially learned and culturally transmitted system: that is, an individual’s linguistic knowledge is the result of observing the linguistic behaviour of others. Here, this well-attested process of language acquisition, often termed Iterated Learning, emphasises the effects of differential learnability on competing linguistic variants. Sounds, words and grammatical structures are therefore seen to be the products of selection and directed mutation. As you can see from the use of terms such as selection and mutation it’s clear we can draw many parallels between the literature on language evolution and analogous processes in biology. Indeed, Darwin himself noted such similarities in the Descent of Man. However, one aspect evolutionary linguists don’t seem to borrow is that of a null model. Is it possible that the changes we see in languages over time are just the products of processes analogous to genetic drift?

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