Regularities in Cultural Evolution

I recently came across a post over at GNXP on the rise and crash of civilizations. It’s a really interesting discussion on a new paper by Currie et al. (2010), Rise and fall of political complexity in island South-East Asia and the Pacific. Here is the abstract:

There is disagreement about whether human political evolution has proceeded through a sequence of incremental increases in complexity, or whether larger, non-sequential increases have occurred. The extent to which societies have  decreased  in  complexity is  also unclear. These  debates have  continued  largely  in the absence  of rigorous, quantitative tests. We evaluated six competing models of political evolution in Austronesian-speaking societies using phylogenetic methods. Here we show that in the best-fitting model political complexity rises and falls in a sequence of small steps. This is closely followed by another model in which increases are sequential but decreases can be either sequential or in bigger drops. The results indicate that large, non-sequential jumps in political complexity have not occurred during the evolutionary history of these societies. This suggests that, despite the numerous contingent pathways of human history, there are regularities in cultural evolution that can be detected using computational phylogenetic methods. [My emphasis].

I don’t have much to add on the subject as I think Razib covered most of the relevant points, plus I haven’t even finished reading the paper yet (I’m hoping to get back into research blogging later this week). I will, however, post one of their figures that shows the dynamic between the rise and fall of political complexity, and how it shows regularity (btw, RJMCMC means Bayesian reversible-jump Markov chain Monte Carlo… if that helps you in any way):

More on Phoneme Inventory Size and Demography

On the basis of Sean’s comment, about using a regression to look at how phoneme inventory size improved as geographic spread was incorporated along with population size, I decided to look at the stats a bit more closely (original post is here). It’s fairly easy to perform multiple regression in R, which, in the case of my data, resulted in highly significant results (p<0.001) for the intercept, area and population (residual standard error = 9.633 on 393 degrees of freedom; adjusted R-Squared = 0.1084). I then plotted all the combinations as scatterplots for each pair of variables. As you can see below, this is fairly useful as a quick summary but it is also messy and confusing. Another problem is that the pairs plot is on the original data and not the linear model.

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Evolution of Colour Terms: 10 Universal Patterns are not Evidence for Innate Constraints

In a series of posts, I’ve been discussing constraints on the evolution of colour terms. Here, I discuss the role of drift and also argue that universal patterns are not necessarily good evidence for innate constraints. For the full dissertation and references, go here.


An important point which has not been highlighted in the literature is the drift introduced by cultural transmission.  Perceptual systems are noisy, and change over lifetimes.  Therefore, systems of categorising these perceptions may drift over time.  However, if concepts are shared, this drift is influenced by more than one system.  This may cause a different kind of drift from a stand-alone system for self-thought.  Communication has an additional semantic bottleneck which self-though does not have.  Using language for self thought, if you don’t know a label, you can make one up.

However, for communication, this won’t work.  For example, in models of cultural transmission (e.g., Steels & Belpaeme, 2005) agents do create new labels but, importantly, accept the speaker’s label when available.  That is, communicative systems are more flexible than systems for self-thought (communicators must be more willing to change their minds), and so are more subject to drift.  The drift allows the system to move around the possible space of coding efficiency and object categorisation efficiency.  Peaks in these landscapes will attract the drift, hence environmental and perceptual constraints being projected into language.

Although systems of colour categorisation for self-thought may be more efficient if they were constrained by the environment, shared cultural systems are more likely to reflect constraints in the environment because they are more flexible.  That is, perceptual constraints have projected themselves into language because of a communicative pressure, rather than a perceptual or environmental pressure.

I suggest that this drift, together with an ability for categories to warp perceptual spaces, would mean that individuals converge on a shared perceptual system.  If comprehension involves the activation of perceptual representations, then communication involves individuals reaching similar perceptual representations or, in a perfect world, activation of the same neural substrates.  Therefore, a population with a shared perceptual system would be able to communicate much more effectively.  In this sense, Embodied systems improve communicative success, whereas the same effect is not necessarily true of Symbolist systems. Furthermore, this drift means that populations can still converge on similar solutions, without having to assume that Universal biases are the main driving force.  It has been argued that the similarities in colour categorisation between cultures contradicts Relativism, which would predict a large variation in colour categorisation between cultures (e.g., Belpaeme & Bleys, 2005).  I argue that this inference is not necessarily valid.


This series of posts has shown that a wide range of factors constrain the categorisation of colour, including the physiology of perception, the environment and cultural transmission.  Why is there evidence for Colour Terms being adapted to so many domains?

This study considered the idea that categorisation acquired by individuals can feed back into perception and itself become a constraint both on the development of categorisation, the environment and genetic inheritance.  In this sense, the feedback from categorisation allows Niche Construction dynamics to apply to linguistic categorisations.  It was argued that this dynamic fits with the Cultural implication of an Embodied account of language comprehension.  That is, this study has concluded, similarly to Kirby et al. (2007), that universal patterns across populations do not necessarily imply strong innate biases.  This was done by arguing that Cultural, Embodied systems tend to drift towards better representations of the real world, which involves better coherence with perceptual and environmental constraints, creating cross-cultural patterns.  Furthermore, an Embodied approach to cultural dynamics incorporating a mechanism for perceptual warping predicts that the perceptual spaces of individuals can be synchronised through language to achieve better communication.

Steels, L., & Belpaeme, T. (2005). Coordinating perceptually grounded categories through language: A case study for colour Behavioral and Brain Sciences, 28 (04) DOI: 10.1017/S0140525X05000087

Belpaeme, T. (2005). Explaining Universal Color Categories Through a Constrained Acquisition Process Adaptive Behavior, 13 (4), 293-310 DOI: 10.1177/105971230501300404

Kirby, S., Dowman, M., & Griffiths, T. (2007). Innateness and culture in the evolution of language Proceedings of the National Academy of Sciences, 104 (12), 5241-5245 DOI: 10.1073/pnas.0608222104

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:

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.


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

Evolution of Colour Terms: 5 Cultural Constraints

Continuing my series on the Evolution of Colour terms, this post reviews studies of cultural constraints on colour naming. For the full dissertation and for references, go here.

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Evolution of Colour Terms: 4 Learning Constraints

Continuing my series on the Evolution of Colour terms, this post reviews how learning constrains colour naming. For the full dissertation and for references, go here.

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Evolution of Colour Terms: 1 Genetic Constraints

Continuing my series on the Evolution of Colour terms, this post reviews the evidence for genetic constrains on colour perception. For the full dissertation and for references, go here.

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Language Evolution and Language Acquisition

The way children learn language sets the adaptive landscape on which languages evolve.  This is acknowledged by many, but there are few connections between models of language acquisition and models of language Evolution (some exceptions include Yang (2002), Yu & Smith (2007) and Chater & Christiansen (2009)).

However, the chasm between the two fields may be getting smaller, as theories are defined as models which are both more interpretable to the more technically-minded Language Evolutionists and extendible into populations and generations.

Also, strangely, models of word learning have been getting simpler over time.  This may reflect a move from attributing language acquisition to specific mechanisms towards a more general cognitive explanation.  I review some older models here, and a recent publication by Fazly et al.

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Language About Language

How is it, then, that we can talk about talking? If you are willing to assume the existence of basic perceptual and cognitive capacities, a relatively simple answer follows immediately. The sounds of talk are, after all, sounds like any other sounds. We can perceive them in the same way we perceive the sound of a waterfall or a bird’s song, a thunderclap or the rustling of leaves in the wind, a cricket’s chirp or the breaking of waves on a beach. All are things we can hear, easily and naturally, and so it is with the sound of the human voice.

Roman Jakobson famously theorized that language has six functions: referential, emotive, poetic, conative, phatic, and the metalingual function. That’s the function we’re interested in, our capacity to speak about speech. Jakobson talked of the metalingual function as an orientation toward the language code, which seems just a bit grand. For I’m led to believe that many languages lack terms for explicitly talking about the ‘code.’ Thus, in The Singer of Tales (Atheneum 1973, orig. Harvard 1960), Albert Lord attests (p. 25):

Man without writing thinks in terms of sound groups and not in words, and the two do not necessarily coincide. When asked what a word is, he will reply that he does not know, or he will give a sound group which may vary in length from what we call a word to an entire line of poetry, or even an entire song. [Remember, Lord is writing about oral narrative.] The word for “word” means an “utterance.” When the singer is pressed then to way what a line is, he, whose chief claim to fame is that he traffics in lines of poetry, will be entirely baffled by the question; or he will say that since he has been dictating and has seen his utterances being written down, he has discovered what a line is, although he did not know it as such before, because he had never gone to school.

While I’m willing to entertain doubts about the full generality of this statement – “man without writing” – I assume the it is an accurate report about the Yugoslavian peasants among whom Milman Parry and Albert Lord conducted their fieldwork and that it also applies to other preliterate peoples, though not necessarily to all.

Given those caveats, the paragraph is worth re-reading. Before doing so, recall how casually we have come to see language as a window on the workings of the mind in the Chomskyian and post-Chomskyian eras. If that is the case, then what can one see through a window that lacks even a word for words, that fails to distinguish between words and utterances? And what of the poets who don’t know what a line is? The lack of such knowledge does not stand in the way of the poeticizing, no more than the lack of knowledge of generative grammar precludes the ability to talk intelligently on a vast range of subjects.

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Language evolution in the laboratory

When talking about language evolution there’s always a resistance from people exclaiming;  ‘but how do we know?’, ‘surely all of this is conjecture!’ and, because of this, ‘what’s the point?’

Thomas Scott-Phillips and Simon Kirby have written a new article (in press) in ‘Trends in Cognitive Science’ which addresses some of the techniques currently used to address language evolution using experiments in the laboratory.

The Problem of language evolution

The problem of language evolution is one which encompasses not only the need to explain biologically how language came about but also how language came to be how it is today through processes of cultural evolution. Because of this potential ambiguity arises when using the term ‘language evolution’. To sort this ambiguity the authors put forward the following:

Language evolution researchers are interested in the processes that led to a qualitative change from a non-linguistic state to a linguistic one. In other words, language evolution is concerned with the emergence of language

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