Dog movie stars and dog breed popularity

A new research I co-authored with Stefano Ghirlanda and Hal Herzog has just been published in PLOS ONE (the paper is open access and can be found here). In this paper we continue our analysis of dog breeds popularity as a particularly interesting (and data-rich) cultural domain. We had already shown that the choice of which puppy one buys seems largely driven by fashion, i.e. social influence, more than by functional considerations (see my post from last year). Now we looked explicitly at one source of social influence, i.e. movies featuring dogs.

We found that indeed there is a strong effect of movies on the popularity of dog breeds. While this is not probably a shocking result, it is quite interesting to have precise quantitative data. We used the AKC database, totalling over 65 million dog registrations from 1926 to 2005, and analysed a total of 87 movies featuring dogs. The impact of movies has been large. We found, for example, that movies have an influence that can last up to 10 years from the initial release. The 10 movies with the strongest 10-years effect are associated with 800,000 more registrations in the AKC then what would have been expected from pre-release trends. A striking example is the 1959 Disney movie The Shaggy Dog. The registrations of Old English Sheepdogs were stable on around 100 dogs per year in the ten years preceding the release of the movie. In 1969 only, ten years after, 4,226 Old English Sheepdogs were registered.

We also found that the more a movie was successful (we estimated the number of viewers from the opening weekend earnings) the more impacted on the popularity of the breeds of the dog featured. Another interesting finding is that the influence of movies has decreased during the century. Earlier movies are in general associated with larger trend changes than later movies. This suggests that movies – perhaps because of an increased competition with other media, such as television, and, more recently, the internet – have gradually lost their influence on pop-culture.

Stefano made a nice figure showing some of the trends (click on it to see a larger version). Both the figure (here) and the data (here) are publicly available on figshare.com

DogMovieStars

Together with our previous results, which showed that behavioural characteristics, longevity, or health were not correlated with breeds popularity, this new analysis provide a quite clear picture: we do not choose, on average, dogs because they are more healthy or, for example, trainable, but because we see them in the neighbours garden, or in the last blockbuster. Why this is not bad per se (copying what others do is a quite effective strategy in many situations) is definitely bad for dogs. The only features that we found to positively correlate with popularity is indeed the presence of genetic diseases. Of course this does not mean that dog owners actively look for breeds with genetic diseases, but, as a minimum, that they do not keep this in consideration when choosing a puppy and, more worryingly, that the huge differences in popularity and the rapid increases of some breeds provoke over-breeding which results, in turn, in an increase of genetic disorders. My take-home message here is: don’t follow fashions when choosing a puppy!

Now a couple of more cultural-evolution related questions. First: how important is how the dog is presented in a movie for the effect on the popularity of the breed? We excluded few movies in which the dog was clearly a negative character (Cujo, for example) but we did not analyse in detail this issue. My feeling is that is not so important. While our data end in 2005, the AKC provides the rankings for more recent years. Hal noted the steady increase of French bulldogs (they were at the 54th position in 2003, and at the 11th last year). It happens that in a famous scene of the hugely popular movie The Hangover, Mike Tyson holds in his arm a French bulldog (see the video below from around 1:30). Since the movie is from 2009 (and we do not have the data…) is not clear whether the movie had an influence on the increase on popularity or if it is the other way around (i.e. the authors capitalised on the growing popularity of the breed and used it for the movie), but the dog is not more than a prop in the scene in question. The idea is that the mere presence of a dog in a popular movie makes it accessible and that, as features of different breeds are, in a sense, neutral (see below), a simple advantage in accessibility generates a cascade of effects (e.g. people will talk about that breed more than about other breeds) that may greatly influence popularity.

(the case of French bulldogs is also relevant for the previous point, as French bulldogs carry – in Hal’s words – a huge load of genetic disorders)

Second: does this result suggest that we are copy-machines, easily influenceable by evil Hollywood’s producers? I do not think so. As I mentioned above I consider the choice of a breed as being, by and large, neutral. This does not mean that all breeds are equal (of course they are not). However, given the choice of owning a dog (this, I think, is a non-neutral choice. Would be interesting to see whether movies influences the total number of dogs in time), the features of different breeds can be reasonably adapted to one’s own habits (or the other way around) so that the choice has, in the majority of cases, not enormous effects on the owners. Many people that are buying French bulldogs now would have probably bought poodles fifty years ago. Something similar happens, for example, for baby names (of course they are different; yes, some of them may have an effect on your life [but see here], but, in the majority of cases, being called Alberto or Stefano does not make much difference). For this kind of cultural traits I would indeed expect social influence and media having a strong effect on popularity, but less for traits that implies more important outcomes. We are not blind copy-machines, but selective copy-machines.

Ghirlanda S, Acerbi A, Herzog H (2014) Dog Movie Stars and Dog Breed Popularity: A Case study on Media Influence on Choice. PLoS ONE 9(9): e106565

What is – and what is not – cultural attraction

A couple of weeks ago, I wrote a post commenting on a recent paper relevant for cultural evolution (Claidière et al. 2014 “How Darwinian is cultural evolution?”). The post prompted a lively and interesting discussion in the comments (thanks to everybody!), focusing on the concept of “cultural attraction”, as presented in that paper and in previous works of Dan Sperber (see e.g. the chapter 5 in “Explaining Culture”).

I thought it could have been useful to summarise here the main points of the discussion, to not let them “buried” in the comments. A few cautionary notes before starting: first, if I misinterpret something I’ll be happy to correct it; second, I need to assume that readers know what I am writing about, this is better intended as a quasi-internal minute.

It seems to me that in the comments we clarified trough successive steps what attraction is not, getting closer (at least for who needed it) to a better understanding of what it is, so I will proceed here in the same fashion.

First, cultural attraction is not restricted to cognitive factors. While the work in the cultural epidemiology tradition has emphasised the importance of cognitive factors in cultural dynamics (in a more than well justified opposition to the “traditional” socio-cultural anthropology of few decades ago), cognitive factors are only one of the possible factors of attraction.

Second, cultural attraction is not to be equated with Boyd and Richerson’s content-based biases. As for the first point, probably nobody involved in the discussion was convinced of that, but this identification happens in the literature so it may be not useless to point it out here. As before, content biases may be factors of attraction in particular cases, but nothing more than that.

Also, cultural attraction is not to be equated with Boyd and Richerson’s guided-variation. Again, the work in the cultural epidemiology tradition has emphasised the importance of constructive processes in cultural propagation, but the claim is that cultural attraction is a more general framework that covers both constructive processes and selection (various Boyd and Richerson’s biases) as a special case.

Finally, cultural attraction is not cultural evolution. Mechanisms such as drift (and possibly others) are in fact mechanisms of cultural evolution, but would not fall under the umbrella of cultural attraction, so that the two cannot be considered equivalent.

This work-in-progress schema may be of some help: cultural attraction does not overlap with cultural evolution, as random (?) forces as drift, and possibly others (question mark on the left) are not considered. On the other side, forces as selection, guided-vairation, migration, etc. can be subsumed under cultural attraction.

attraction

I think Dan and Thom made a great job in explaining how exactly attraction should be related to concepts that are already present in cultural evolution and, also, there may indeed be a point in having a general concept (attraction) that “goes together with a unitary way of modelling things”.

Let me finish with three thoughts that may (or not) stimulate further discussion:

1) I think it would be helpful to re-state an explicit definition of attraction. In the paper is written:

the constructive processes we discussed above may tend to transform different inputs in similar ways (rather than randomly), and in doing so cause the outputs to tendentially converge upon particular types, called attractors. This tendency is called cultural attraction.

But this would be again the “narrow” version of attraction (the same happens in the Summary “[...] The process by which they do this is called cultural attraction”), so I assume a more general definition, like this one (also from the paper):

the possibility that every item of every type at t may have some causal effect on the frequency of items of every type at t+1

Or something else?

2) Generality is surely good, but, to use again the biological case as comparison (and keeping in mind the Godfrey-Smith schema): since biologists can usually assume hi-fidelity transmission, they are in the advantage position of being less general. Thus the need for generality in cultural evolution is not good per se, but it is linked to the particular importance of non-preservative processes, which is, again, an empirical question.

3) Finally, a practical question: what should we do with the sophisticated formal models already developed for, say, selection-based processes? Would they need to be rewritten in the more general attraction terms (as the example you give in the paper), or one could – when a cultural domain is considered enough preservative, say first names – keep on using the existent models?

If we’re all cultural darwinians what’s the fuss about?

An important paper from Nicolas Claidière et al., “How Darwinian is cultural evolution?” appeared recently in Philosophical Transactions of Royal Society B. 

Claidière and coauthors adopt a useful schema from the philosopher Peter Godfrey-Smith to distinguish “how darwinian” an explanatory framework can be considered. At the more general level, an explanation can be considered “populational” if considers “a system (such as culture) as a population of relatively autonomous items of different types with the frequencies of types changing over time” (Claidière et al. 2014). A second step is needed to qualify the explanation as “evolutionary”, that is, the frequencies of those types at time are a function of their frequencies at time t-1. All cultural evolution explanatory frameworks are both populational and evolutionary (I do not consider here vast amounts of socio-cultural anthropology).

Things get more interesting at the next two levels, i.e. the “selectional” and the “replicative”. The former implies that the above types should exhibit variation, heritability, and fitness differences, while the latter adds a further constraint, that is that they should also replicate themselves. While only strict memeticists claim that cultural evolution is darwinian in all four senses, Claidière et al. argue that the correct explanatory framework for cultural evolution is not even the selectional one.

The dispute is about the fidelity of cultural transmission. For memeticists, the problem does not exist, as fidelity is sufficient to consider cultural transmission as a proper process of replication (as it is considered in biological evolution). For “standard” cultural evolutionists, rates of mutations of cultural items are higher than in genetic transmission, but it is still useful to consider in general the cultural success of an item as a result of selection among competing variants. According to Claidière et al. however this is, in the majority of cases, incorrect, as cultural traits do not propagate trough a process of copying (with more or less fidelity) but they are reconstructed each time. For example, I am trying here to report with high fidelity the cultural trait “How Darwinian is cultural evolution?”, but I am certainly modifying it, making it shorter in respect to the original version, focusing on parts that am particularly interested, misinterpreting and misunderstanding (my fault) what authors wanted really to transmit. Even worst, what you, reader, will recall of this post, will be even different (if anything). All this, for a transmission chain of two or three passages.

Claidière et al. reformulate and extend a concept that the anthropologist Dan Sperber proposes from a long time: cultural evolution forces are better thought in terms of attraction then in terms of selection. The various forces that transform cultural items during the reconstructive processes are not random, but they tend to act in a consistent, even when weak, direction, making cultural outputs converge toward particular “attractors”. Sperber and colleagues generally focuses on cognitive forces. For example, some features of a story are easier to remember than others, and they will serve as attractors when the story is re-constructed. Eric Havelock (about which I read in Rubin, 1995) suggests that this is indeed a function of heroes and gods in epics and ballads that were orally transmitted. Heroes and gods are “bags of attractors” (that’s neither Havelock nor Rubin expression), as they have fixed and concrete features that are easy to image and to remember, which help narrators both to describe abstract concepts and to organise the narration in familiar sequences (Levi-Strauss often cited aphorism on animals “good to think with” should go in a similar direction).

While I am generally sympathetic with this proposal (as well as a Dan Sperber’s fan), I think there are few points worth to discuss. The first concerns the notion of “attraction”, and the fact that is often understood in different ways (and the effort of Claidière et al. to present a clear definition is certainly welcome), being sometimes equated to Boyd and Richerson’s content bias (by me, for example). The second, more interesting, concerns the issue of reconstruction versus replication preservation. The question whether cultural propagation is better described as one or the other is an empirical one, and the answer varies for different cultural domains. Claidière et al. agree with that, but claims that “a large number” of cultural propagations are results of reconstructive processes. Perhaps. Without entering in technical details on how exactly copying fidelity should be considered (which are anyway useful), there should be a continuum between ideally pure individual innovation and virtually error-free copying (this continuum being wider than in the biological case), and, depending on the domain we consider, we may want to “move” in the Godfrey-Smith’s schema.  I’ll try to write more on that soon.

[Much more interesting stuff below in the comments. Thanks in particular to two of the authors of the paper discussed, Thom Scott-Phillips and Dan Sperber, and to Alex Mesoudi and Tim Tyler. Also, the discussion continues here.]

“Journal of Cultural Evolution”: some material to discuss

In preparation of the meeting of next week (13:00, Wednesday 9 April at EHBEA in Bristol, see my previous post and the conference program), I post here some material we plan to discuss.

On the operative side there is one important news: we had a meeting with Peter Turchin (see his excellent Social Evolution Forum) who proposed the possibility to join forces. Peter is the editor in chief of “Cliodynamics: The Journal of Theoretical and Mathematical History“. In short, this option would involve broadening the scope of the existent journal (now mainly focused on historical, long-term, processes) to include other dimensions of cultural evolutionary studies, and changing the title – and renewing the editorial board – so to reflect the new scope. Notice this option will depend both on what we will discuss on the meeting and on the decision of the current editorial board of  Cliodynamics.

The journal currently publishes peer-reviewed articles in electronic-only form, and it is based on the eScolarship platform from the University of California.  Access is completely free (as it happens, in general, in Open Access journals), and no fees are required to publish (as it does not happen, in general, in Open Access journals). This model can be sustained by a mix of voluntary work and external fundings: if I understood correctly, a person supported by a grant is currently working part-time on it, and this grant will last for the next three years (so that, in principle, we would not necessary need, at least for the first period, other fundings).

An appealing aspect is that the journal has been submitted almost three years ago to Thomson Reuters’ review, so that, if the process will go smooth, it will be soon indexed in the Web of Science, which means, notably, that it will have an Impact Factor. (However, it is very important to understand exactly the effect of a potential change of name, scope, etc. on this process).

If one considers this publishing model appropriate, there are several advantages in pursuing this option, including importantly that the “platform” (by which I mean organisational as well as technical aspects) is already in place, and it could be used for a relatively prompt launch (“prompt” being intended with reference to the publishing time system).

For the sake of debate, one might legitimately prefer a more traditional publishing model, so to be sure to have on the side an experienced publisher and to concentrate on the more “scientific” aspects of the endeavour. Also, I understand a certain psychological attraction of having a “shiny” new start of the enterprise. Finally – but this may be my idiosyncrasy – why all the not-from-a-big-publisher academic journals that I know seem to look aesthetically unpleasant? Does it need to be like that?

See you in Bristol to discuss about it  – and, again, comments below are encouraged!

“Journal of Cultural Evolution” meeting at EHBEA 2014

Some months ago I wrote a post mentioning the difficulties that, at times, people working in the interdisciplinary field of “cultural evolution” may face in order to find an appropriate scientific journal to submit their research. Also, I wondered whether, given that the general feeling seems to be that the field is quite coherent, and that it is starting to be “mature”, it was perhaps time for a “Journal of Cultural Evolution” (If all this does not make much sense please go to the aforementioned post).

I was pleased to see that the reaction was  generally positive  – and, above all, that there was a reaction - which made me think that probably I was exposing a common concern, and indeed many people thought that there was an empty niche in the academic publishing that one could fill.

Therefore, with Fiona Jordan, we are organising a meeting at EHBEA 2014 (the European Human Behavior and Evolution Association Conference, which will be held in Bristol from 6 to 9 April, and which is with no doubts a cultural evolution-friendly conference) to discuss about this project, and possibly to start to do something concrete in this direction.

The meeting, which will be short and informal, will be Wednesday 9 April at 13.00 (lunchtime) in the conference venue (I’ve been told that people tend to run to pubs  at the end of the day after the talks; and anyway the lunch is provided on-site by the conference, so we would be there in any case).

I’ll try to post in the next days some material to start a discussion, but of course I’d be very happy if someone want to use this space (or elsewhere) to share some ideas before the actual meeting. Also, please, circulate the information to cultural evolutionists and EHBEA-goers who happen to not read this blog (shame on them).

See you in Bristol!

Detecting cultural transmission biases in real-life dynamics

Many studies of cultural evolution have focused on how transmission biases affect the likelihood of cultural traits of being transmitted. The concepts are quite intuitive. An useful distinction is between content biases, when the intrinsic features of a cultural trait makes it more likely to spread (the effectiveness of a tool may be a content bias, but also a sexual hint in an image), and context biases, when the likelihood is determined by the context, as when we tend to dress as our friends/coworkers (conformist bias; but one can do the opposite, and prefer unpopular cultural traits), or as when I was trying to have a young Axl Rose haircut (prestige bias – see also my picture on the left).

Some interesting works in cultural evolution have examined, with analytical and simulation models, the adaptivity of transmission biases (e.g. did my Axl Rose haircut make me rich and/or attractive? It did not, but, on average, prestige bias may be useful) or examined the transmission biases long-trend dynamics in idealised situations (e.g. how fast will a new cultural trait “invade” a population of conformist individuals? or of anti-conformists? etc.). Other works investigated, in controlled experiments, if people are indeed subject to transmission biases when copying from others (they are, with caveat).

What is partly missing is an understanding of the impact of transmission biases in real life cultural dynamics. We recently had a paper accepted in Evolution and Human Behavior that tackles this problem.  In brief (much more is in the paper!): (1) we focused on the turnover of popular traits, i.e. on how many new traits enter in a top-list of a certain size for a certain cultural domain (like here); (2) we used some predictions on how the turnover would look like  if there were no biases, that is, if everybody would just copy others at random (neutral model of cultural evolution); and (3) we showed how these predictions differ if biases are instead present.

turnover

The turnover of some cultural domains, for example recent baby names in USA, looks like the red line in the figure above, signalling that people tend to prefer relatively un-common names. The turnover of others, like early baby names, musical preferences of Last.fm users who subscribed to genre-based groups (“80s Gothic”, “Acid Jazz”) , or usage of colour terms in English language books, looks instead like the blue line, signalling a conformist bias, or a content-based bias (which I call “attraction”).

Overall, turnover can be calculated when we have periodical top lists, or, more generally, when we can “count” the frequency of items trough time. Given the ubiquity of this kind of information in digital form, one can use this methodology to infer individual behaviour from population-level, aggregate, data for several cultural domains.

Acerbi, A. and Bentley, R.A. (2014), Biases in cultural transmission shape the turnover of popular traits, Evolution and Human Behavior, in press.

Books Average Previous Decade of Economic Misery

Almost one year ago, we published a paper in which we described a large scale analysis of cultural/literary trends, realised using the google books ngram corpus. In particular, we showed that, trough a relatively simple extraction of emotion-realted words (words semantically related to “main” emotions like joy, sadness, anger, etc.), it was possible to detect some clear tendencies, such as a general decline in the emotional “tone” of books published in the twentieth century – or at least in the frequencies of emotions words -, a divergence between American and British English – with the former being more emotional -, and, finally, the existence of distinct periods of “literary mood” in the last century.

Related to the last point, PLOS ONE just published a follow up of this research, in which we correlate this literary mood with the past century economic trend. The image below shows the main point of our study.

misery

The red line is what we called “Literary Misery Index” (how “sad” are books in a certain year, on average), that we extracted from the books in the Google Corpus, while the black line is a 11-years moving average of the economic Misery index (how “bad” is economy in a certain year), a well-known economic index, realised adding inflation and unemployment rates. The two trends are strongly correlated (you can read more in the Bristol University press release here, and, of course, in the original paper).

As for the previous work, we are glad we had some media attention (see for example The New York Times and The Guardian), which generated quite a lot of buzz. Not surprisingly, this included some criticism. It is interesting that, while some commenters think that we are “stating the obvious”, others accuse us to apply  a “crude” causal determinism, and to defend the implausible claim that economy “dictates” literature and culture.

To me, I am more sympathetic to the state-the-obvious side of the debate so I am not going to write on this (but: we are able to substantiate an “obvious” claim – economic conditions influence cultural mood – with empirical data, as well as provide some refinement, for example providing a possible estimate of a time lag). Regarding the other side of the debate, I would not say that economy “dictates” literature, but it is quite plausible that economic conditions may have an effect on mood. This is not just common sense: many studies link, for example, financial strain and depressive symptoms (here), or general psychological distress (here). If the google corpus is a good barometer of a culture mood, our results are not particularly surprising. This does not mean of course that all books published, for example, in the 80s, were gloomy (I feel like I am underestimating the intelligence of the readers, but some journalists seem to criticise our result on this shaky basis), or that economy alone has a causal effect on literature or culture.

On a related note, given that I can safely assume that most of the “crude determinism” critics come from literary, or, in general humanistic, departments: I like to imagine that a well-known German philosopher, that once was very praised in there, would be very supportive of our work!

KarlMarx

Reference

Bentley R.A., Acerbi A., Ormerod P., Lampos V., (2014), Books Average Previous Decade of Economic MiseryPLoS ONE, 9 (1): e83147.

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