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How spurious correlations arise from inheritance and borrowing (with pictures)

James and I have written about Galton’s problem in large datasets.  Because two modern languages can have a common ancestor, the traits that they exhibit aren’t independent observations.  This can lead to spurious correlations: patterns in the data that are statistical artefacts rather than indications of causal links between traits.

However, I’ve often felt like we haven’t articulated the general concept very well.  For an upcoming paper, we created some diagrams that try to present the problem in its simplest form.

Spurious correlations can be caused by cultural inheritance 


Above is an illustration of how cultural inheritance can lead to spurious correlations.  At the top are three independent historical cultures, each of which has a bundle of various traits which are represented as coloured shapes.  Each trait is causally independent of the others.  On the right is a contingency table for the colours of triangles and squares.  There is no particular relationship between the colour of triangles and the colour of squares.  However, over time these cultures split into new cultures.  Along the bottom of the graph are the currently observable cultures.  We now see a pattern has emerged in the raw numbers (pink triangles occur with orange squares, and blue triangles occur with red squares).  The mechanism that brought about this pattern is simply that the traits are inherited together, with some combinations replicating more often than others: there is no causal mechanism whereby pink triangles are more likely to cause orange squares.

Spurious correlations can be caused by borrowing


Above is an illustration of how borrowing (or areal effects or horizontal cultural inheritance) can lead to spurious correlations.  Three cultures (left to right) evolve over time (top to bottom).  Each culture has a bundle of various traits which are represented as coloured shapes.  Each trait is causally independent of the others.  On the right is a count of the number of cultures with both blue triangles and red squares.  In the top generation, only one out of three cultures have both.  Over some period of time, the blue triangle is borrowed from the culture on the left to the culture in the middle, and then from the culture in the middle to the culture on the right.  By the end, all languages have blue triangles and red squares.  The mechanism that brought about this pattern is simply that one trait spread through the population: there is no causal mechanism whereby blue triangles are more likely to cause red squares.

A similar effect would be caused by a bundle of causally unrelated features being borrowed, as shown below.


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Persister: A sci-fi novel about cultural evolution and academic funding

Someone has written a sci-fi space opera about a serial killer that targets researchers of cultural evolution which is also a satire on the state of academic funding systems.

That’s quite an action-packed sentence.

Persister: Space Funding Crisis I by Casey Hattrey is a short novel set in the 45th century about a cultural evolution researcher named Arianne. By this point, the decision process for academic funding takes so long that the only sensible option is to cryogenetically freeze yourself while you wait for the decision to come in. The cost of this, and the fierce competition for funding in a pan-galactic community, has made the Central Academic Funding Council Administration the most powerful force in the galaxy. Now, Arianne has been woken from chryo-sleep, not to be given a grant, but to investigate a series of gruesome murders. Someone has been killing the top researchers in the field of cultural evolution.

"In space, no one can hear you apply for funding"

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Some Quick Thoughts on Cultural Evolution

Here are some thoughts I’ve been having on cultural evolution. All of them need fuller exposition, but I don’t have time for that now.

1. Cultural Evolution, so What?

I’ve got a fairly sophisticated narrative account of some varieties of popular music in 20th century America. The account centers on the interaction between African- and European-American populations and musical forms. When I was doing that work–in the late 1990s–I kept thinking that this is the kind of phenomenon that begs for an account in terms of cultural evolution. But I didn’t once use the term “memes” (my term of choice at the time) in the paper nor did I talk of cultural evolution (except in passing at the very end). It’s not at all obvious to me how any existing account of cultural evolution would lead to a deeper understanding of that history. It would just be an exercise in terminology mongering.

This is a very big deal for me, and I don’t yet know what to do about it.

On African American music and so forth, see Music Making History: Africa Meets Europe in the United States of the Blues.

2. Information and Apple Pie

On information, sure, at the highest level of generality and abstraction cultural evolution involves information. But that doesn’t get us much in itself. Until we understand how that information is embodied in the brain and in various media and can measure it, the idea isn’t a very useful or deep one. It’s one of mere terminology, verbal packaging. But see comment seven, below.

3. Information, DNA, the Brain and the Rest

In biology we know that genetic information is embodied in DNA and we know a great deal about how that works. And we are rapidly increasing our ability to manipulate DNA.

We don’t know how information is encoded in the nervous system. But that’s not so much my point here. It belongs in #2 above.

My point here is that, in long-held view, the genetic information for culture isn’t in the brain. It’s in publicly accessible traits of physical objects and processes. That means that, whereas the genetic information of life forms is encoded in the same medium, DNA, that is not the case for cultural genetic information. The genetic information for culture has various embodiments.

From the standpoint of theoretical elegance/parsimony, this is not so good. But the fact is, no matter what kind of model you choose, if you want to deal with information, you are going to have to deal with multiple physical embodiments and the transformations between them.

4. Mutual Information for Culture

We’re interested in the ‘conservation’ of information in the social group. That requires shared access to common reference points. The meaning of those reference points is, in effect, negotiated through interaction. Those agreed reference points are the ‘genes’ of the cultural process.

Compare this with DNA replication. The double strand divides and then each half constructs the necessary complement. The result is two identical DNA molecules where there had been one.

Shared access to a common public reference plays the role in cultural informatics that DNA replication plays in biological informatics.

On mutual information in culture, see my Open Letter to Steven Pinker.

5. The mind as computer program

Programs have variables and variables require values. Where do mental programs get values for their variables? Some of them are generated internally.

And some of them come from the external world. Among those we have the cultural genetic material. They function as values for variables in mental programs.

See this post for further specification of this thought: Memes as Data: Targets, Couplers, and Designators. That is collected in my working paper, Cultural Evolution, Memes, and the Trouble with Dan Dennett. Continue reading

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How Language Evolves Webcast

CARTA (Center for Academic Research & Training in Anthropogeny) are webcasting their free symposium on “How Language Evolves” on Friday, February 20th (1:00 – 5:30 pm PST), co-chaired by Roger Levy (UC San Diego) and David Perlmutter (UC San Diego).

How Language Evolves


The symposium addresses the question of how human language came to have the kind of structure it has today, focusing on three sources of evidence:

1) ways languages get new structure not present in the language of the previous generation(s) of speakers or signers;

2) what contrasts between new and mature languages reveal about how language evolves;

3) neuroscientific investigations of functional specialization for language in the human brain and its dependence on the linguistic input the language learner gets during cognitive development.

You can access the live webcast here:



Empty Constructions and the Meaning of “Meaning”

Textbooks are boring. In most cases, they consist of a rather tiring collection of more or less undisputed facts, and they omit the really interesting stuff such as controversial discussions or problematic cases that pose a serious challenge to a specific scientific theory. However, Martin Hilpert’s “Construction Grammar and its Application to English” is an admirable exception since it discusses various potential problems for Construction Grammar at length. What I found particularly interesting was the problem of “meaningless constructions”. In what follows, I will present some examples for such constructions and discuss what they might tell us about the nature of linguistic constructions. First, however, I will outline some basic assumptions of Construction Grammar. Continue reading

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Tone and Humidity: FAQ

Everett, Blasi & Roberts (2015) review literature on how inhaling dry air affects phonation, suggesting that lexical tone is harder to produce and perceive in dry environments.  This leads to a prediction that languages should adapt to this pressure, so that lexical tone should not be found in dry climates, and the paper presents statistical evidence in favour of this prediction.

Below are some frequently asked questions about the study (see also the previous blog post explaining the statistics).

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Cultural Evolution: Literary History, Popular Music, Cultural Beings, Temporality, and the Mesh

Another working paper (title above):

Abstract and introduction below.

* * * * *

Abstract: Culture is implemented in a material and biological substrate but has a distinct ontology and its phenomena belong to a distinct order of temporality. The evolution of culture proceeds by random variation among coordinators, the cultural parallel to biological genes, and selective retention of phantasms, the cultural parallel to biological phenotypes. Taken together phantasms and a package or envelope of coordinators constitute a cultural being. In at least the case of 19th century American and British novels, cultural evolution has a direction, as demonstrated by the analytical work of Matthew Jockers (Macroanalysis 2013). While we can think of cultural evolution as a phenomenon that happens in history, it is at the same time a force that influences human life. It is thus a force IN history. This is illustrated by considering the history of the European novel from the 19th century and into the 20th century and in the evolution of popular musical styles in 20th century American music, in which interaction between African American and European American populations has been important. Ultimately, the evolution of culture can be thought of as the evolution of mind.

* * * * *

0. Introduction: The Evolution of Culture is the Evolution of Mind

One of the themes that has been prominent in Western culture is that we humans have a “higher” nature and a “lower” nature. That lower nature is something we share with animals, even plants–I’m thinking here of Aristotle’s account of the soul. That higher nature is unique to us and we have tended to identify it with reason and rationality. We are rational and can reason, animals are not and cannot.

It was one thing to hold such a belief when we could believe that our nature was distinct from that of animals. Darwin made that belief much more difficult to entertain. If we are descended from apes, and so are but animals, then how can we have this higher nature? And yet, by any reasonable account, we are quite different from all the other animals.

For one thing, we have language. Yes, other animals communicate, and, with much painstaking effort, we’ve managed to teach some sign language to chimpanzees, but still, no other species has yet managed anything quite like human language. And the same goes for culture. Yes, other animals have culture in the sense that they pass behavioral traits from one individual to another through social learning rather than through reproduction. But the trait repertoire of animal culture is quite limited in comparison to that of human culture. Nor has any animal species managed to remake their environment in the way we have, for better or worse, not beavers and their dams, nor termites and their often astounding mounds.

In the process of working through the posts I’ve gathered into the this working paper, the original writing and the subsequent reviewing and revising, I’ve come to believe that it is culture, not reason, that is our higher nature. Reason is a product of culture, not the reverse.

That conclusion is not a direct result of the post’s I’ve gathered here. You won’t find it as a conclusion in any of them, nor will I provide more of an argument in this introduction than I’ve already done. It’s a way of framing my current view of culture and human nature. It’s a higher nature. It rules us even as it is utterly dependent upon us.

Conceptualizing Cultural Evolution

This working paper marks the fruition of a line of investigation I began in 1996 with the publication of “Culture as an Evolutionary Arena” (Journal of Social and Evolutionary Systems, 19(4), 321-362). That was not my first work on cultural evolution; but my earlier work, going back to graduate school in the 1970s, was about stages conceived in terms of cognitive systems (called ranks). That work was descriptive in character, aimed at identifying the types of things possible with a given cognitive apparatus. The 1996 paper was my first attempt at characterizing the process of cultural evolution in evolutionary terms.

That paper originated in conversations I’d had with David Hays, who died in 1995, in which he suggested that the genetic material for cultural evolution was in the external world. Why? Because it is public, open for everyone to see. If the genetic material was out there in the world, I reasoned, then the selective environment must be social, something like a collective mind. That made sense because, after all, isn’t that how books and movies and records survive? Many are published, but only a few are taken up and kept in active circulation over the years.

That’s not much of a conception, but I stuck with it. It’s taken almost two decades for me to refine those initial intuitions into a technical conception that feels good. That’s what I managed to achieve in the process of writing the posts I’ve collected and edited into this working paper.

All of which is to say that I’ve been working on two levels. On the one hand I’ve been making specific proposals about specific phenomena. But those specific proposals are in service of a more abstract project: crafting a framework in which to conceptualize cultural evolution. By way of comparison, consider chapter eleven of Richard Dawkins, The Selfish Gene. That’s where he proposes the concept of memes in thinking about cultural evolution: “Memes: the new replicators” (pp. 189-201). He gives a few examples, but mostly he’s focused on the concept of the meme itself. The examples are there to support the concept. None of them are developed very extensively or in detail; he says just enough to give some sense of what he has in mind.

THAT’s what I’m doing, though proportions and quantities are different. It is the concept of cultural evolution that most interests me: what’s it like, what kind of entities does it involve? The example from Matthew Jockers’ Macroanalysis in the first two posts is just that, an example. In subsequent posts I introduce further examples, but they are just that, examples. Continue reading


Tone and humidity

Does the weather effect the languages we speak?

This week, Caleb Everett, Damian Blasi and I have a paper out in PNAS (also available here) on the effects of humidity on the production and perception of lexical tone, and the subsequent predictions about the distribution of tone across the world.

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Map of humidity (lighter = more humid) with complex tone languages in red and non-complex tone languages in blue.

The basic principle behind studies of cultural evolution is that a selective pressure on communication can transform the structures of a language over time.  What we explore is whether speaking in dry environments exerts a pressure to avoid using sounds that are more difficult to produce or comprehend, leading to those sounds being selected against.

Edit: See also this FAQ page

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Issues in Cultural Evolution 2.2: ‘Cultural Genes’ are Out There in the World

I think the thing to do at this point is post a version of my own view of cultural evolution, but one that skips the terminology that I’ve recently adopted. In this version, which more or less centers on my 1996 article, Culture as an Evolutionary Arena, I adopt the term “meme” as the name of the genetic entities of culture. Though I’ve recently dropped the term, I’ll use it in this post.

Gavagai and Conduits

First, though, I want to think a bit about the problem of evolving a communication system.

Some years ago I was engaged in an email conversation with Valerius Geist, a naturalist, who pointed out that biological communication systems are very conservative because they have to evolve two sets of matched traits. They’ve got to evolve a system to emit signals – vocal calls, gestures, postures – and one that understands those signals. These two systems have to match. If they don’t, the communication will fail.

Culture has the same problem, which we can illustrate with a classic thought experiment in the philosophy of language. This is from Willard van Orman Quine, Word and Object (1960). He asks us to consider the problem of radical translation, “translation of the language of a hitherto untouched people” (Quine 1960, 25). Consider a “linguist who, unaided by an interpreter, is out to penetrate and translate a language hitherto unknown. All the objective data he has to go on are the forces that he sees impinging on the native’s surfaces and the observable behavior, focal and otherwise, of the native.” That is to say, he has no direct access to what is going on inside the native’s head, but utterances are available to him. Quine then asks us to imagine that “a rabbit scurries by, the native says ‘Gavagai’, and the linguist notes down the sentence ‘Rabbit’ (of ‘Lo, a rabbit’) as tentative translation, subject to testing in further cases” (p. 25).

Quine goes on to argue that, in thus proposing that initial translation, the linguist is making illegitimate assumptions. He begins his argument by nothing that the native might, in fact, mean “white” or “animal” and later on offers more exotic possibilities, the sort of things only a philosopher would think of–one of the possibilities was “mere stages, or brief temporal segments, of rabbits” (p. 46). Quine also notes that whatever gestures and utterances the native offers as the linguist attempts to clarify and verify will be subject to the same problem. Quine’s argument is thorough and convincing.

This situation, of course, is rather different from that of ordinary speech between people who share a common language. In the common situation both parties would know the meaning of “Gavagai.” Yet, however effective it is, ordinary speech sometimes fails to secure understanding between people and, when such understanding is achieved, that achievement has required back-and-forth speech. The mutual understanding is achieved through a process of negotiation. As William Croft reiterates in chapter 4 of Explaining Language Change, we cannot get inside one another’s heads and so must negotiate meanings in conversation.

That is to say, communication through language is not a matter of sending information through a pipeline. It does not happen according to what Michael Reddy (1993 in Ortony, Metaphor and Thought) has called the conduit metaphor. Reddy’s article is based on 53 example sentences. Here are the first three (p. 166, italics in the original):

1. Try to get your thoughts across better
2. None of Mary’s feelings came through to me with any clarity
3. You still haven’t given me any idea of what you mean

Reddy’s argument is that many of our statements about communication seemed to be based on the notion of sending something (the thought, idea, feeling) through a conduit, hence he calls it the conduit metaphor. He knows that communication doesn’t work that way, but that’s not his central issue. His central concern is to detail the way we use the conduit metaphor to structure our thinking about communication.

Of course, language is not the only medium of human communication and culture. One can craft a wheel that’s just like an existing wheel without having to know what the wheelwright was thinking. As long as your wheel is acceptably like existing wheels, it is OK. How you made it is secondary. Even there, of course, you can observe a master wheelwright at work and imitate his process. One can learn music through imitation as well.

That is, as long as there is a publicly visible physical model, of an object or a process, one can learn how to make the object or perform the process through imitation, hence the emphasis on imitation in the memetics literature. Imitation fails, however, when it comes to the meanings of words. You can learn to imitate sounds, but not meanings. The learning of meaning is different, and it is something that’s been all but ignored in the orthodox memetic literature. That literature assumes that we “transfer information” like sending oil or water through a pipeline. It uses a reified concept of information to dissolve the problem, rather than solve it. It is not well-informed about cognitive science and linguistics and so cannot be considered intellectually serious. Continue reading

call for papers

Reminder for upcoming conferences

The deadline is approaching for several relevant call for papers:

At this year’s International Congress of Phonetic Sciences in Glasgow there will be a special interest group on the Evolution of our phonetic capabilities. It will focus on the interaction between biological and cultural evolution and encourages work from different modalities too. The deadline is 16th Feb. The call for papers is here.

There’s also a special discussant session on Sound change and speech evolution at ICPhS headed by Andy Wedel. The deadline for the actual conference is 1st Feb. Call for Papers here.

The next event in the ways to (proto)language conference is being held in Rome! The deadline is also 1st Feb. Call for Papers here.

This year’s CogSci is being organised by the guys at Cognitive and Information Sciences at the University of California in Merced, who do some great stuff related to language evolution. The deadline is 1st Feb as well, and the call for paper is here. 

Happy submitting!

Culture, its evolution and anything inbetween