cultural evolution

The interplay of genetic and cultural evolution

In my last post, I discussed the framework for cultural evolution laid out by Claire El Mouden and colleagues in a new article in the Journal of Evolutionary Biology (ungated pdf and supporting information). By setting out clear definitions for the analysis of cultural evolution, such as cultural relatedness and fitness, a workable framework using evolutionary biology’s Price equation can be developed.

As I noted in that post, it is when the biological and genetic frameworks are laid on top of each other, as is the focus of the dual-inheritance literature, that things get interesting. With their framework, El Mouden and friends tackle a couple of the prominent gene-culture evolution questions.

The first question is to what extent cultural evolution increases or decreases genetic fitness. The authors note that a theme of the gene-culture evolution literature is that cultural evolution made the scale and distribution of today’s human population possible. How does this work?

For there to be a positive correlation between cultural and genetic fitness, those who have the most cultural influence must also leave the most offspring. It is easy to see circumstances where this holds, with those of high social status tending to have both cultural influence and more offspring (look at the number of partners of rock stars).

An example to the contrary is low fertility in developed countries. El Mouden and colleagues reference work by Richerson and Boyd, who suggest that high status is given to professions with high investment in education, which would allow the behaviour to spread despite the negative relationship between education and fertility.

However, El Mouden and friends show that this mismatch between cultural and genetic fitness is evolutionarily unstable as genetic natural selection acts to align genetic and cultural fitness. They suggest two reasons for this, one involving transmission and the other selection.

Their transmission explanation relies on the already evolved propensity for people to avoid behaviours that are harmful to their genetic interests. For example, the nausea produced when consuming toxins would fight against any cultural pressure to eat toxic food. However, it is an interesting question as to how general this transmission effect would be, as many cultural forces are novel and without precedent in our evolutionary history. Transmission may be unlikely to constrain our desire for high status professions that require large investments in education any time soon.

The genetic selection explanation would seem to have broader power. In the supplementary information, the authors ask us to consider a population where cultural and genetic fitness were not aligned. Now, imagine a mutant in that population that causes people to pay attention to a cultural trait that is more highly correlated with genetic fitness. As these mutants have higher genetic fitness, they increase in proportion of the population, and cultural and genetic fitness are now more correlated. Cultural fitness now promotes genetic fitness. In the long-run, the two will be perfectly correlated (the exception being where cultural traits are neutral to genetic fitness).

The catch in that last sentence is the “long-run”. As cultural evolution can be so much faster than genetic evolution, systems can be far from genetic equilibrium until the genetic response evolves. Fertility in developed countries would be an example of this. There may also be some constraints that prevent perfect alignment, such as the presence of appropriate learning mechanisms.

This interaction of genetic and cultural evolution gets most interesting is when we turn to the evolution of altruism. In examining this question we must remember that genetic and cultural fitness are distinct. Cultural altruism reduces the altruist’s cultural fitness; that is, their influence. As a result, the claim that cultural evolution increases genetic altruism (the more common claim in the gene-culture evolution literature) needs to be made carefully.

As an illustration, consider this interesting example from the paper. A stranger is being attacked, so a good Samaritan steps in to defend them and dies as a result. Whether this is culturally altruistic would depend on whether the Samaritan’s deed was copied. If so, then the Samaritan’s act would actually have been increase cultural fitness as it would have increased their influence in respect of that cultural trait.

Conversely, their death is genetically altruistic. As a result, genetic selection would tend to act against it. Those who ignore this cultural trait will have higher genetic fitness, grow in proportion of the population and eventually bring cultural and genetic fitness into alignment.

So what of behaviours that are both culturally and genetically altruistic? Whether the behaviour spreads will depend on the degree of cultural and genetic relatedness.

Evidence suggests that cultural relatedness within ethnic groups is higher than genetic relatedness (although it is still not high in absolute terms, with more within group than between group variation). This means that there are a wider range of circumstances for which cultural altruism can emerge than for genetic altruism. However, that domain in which cultural but not genetic altruism is likely to emerge will be subject to the forces described above to align cultural and genetic fitness.

Another important point is that each cultural trait should be considered separately. Even though a group may have the same language, giving them high relatedness for this cultural trait, this does not mean that they have the same views on giving their lives for strangers, for which they may have low cultural relatedness. Consideration of the conditions for altruism need to consider the specific cultural trait.

There are many other interesting points in the article – I recommend reading the whole thing – but I will close with a point on the practicality of modelling cultural evolution in this way. El Mouden and friends note that there is a host of complications not present in the genetic case. Cultural relatedness can vary wildly across cultural traits, whereas the nature of genetic transmission means that relatedness is similar across most of the genome. Recognising the pattern of inheritance is also a challenge, as ancestor numbers can vary in number and be of vastly different biological ages. In that context, there is no such thing as a standard length of generation.

So although this paper presents a nice approach to cultural evolution, it does not present an approach that is easily applied to empirical observation. However, given the lack of clarity across much of the gene-culture evolution literature, particularly when examined across authors and papers, it is nice to see an attempt to achieve some conceptual coherence.

Doing cultural evolution right

A sojourn into the literature on cultural evolution can be confusing. Authors use the same terms in different ways. Unique models are used to reach opposite conclusions. And each author seems to find their own way to intertwine genetic evolution into the analysis.

In that light, a new article in the Journal of Evolutionary Biology (ungated pdf and supporting information) by Claire El Mouden and friends seeks to nail down some of the concepts of cultural evolution and to set up a general framework (thank you!). The paper is at a more basic level than that of Geoffrey Hodgson and Thorbjørn Knudsen’s book Darwin’s Conjecture, which also sought to define and generalise concepts in this area.

El Mouden and her colleagues’ paper covers a lot of interesting terrain, so I will cover it in two posts. In the first, I’ll cover the basics of a cultural evolution framework. In the second, I will look at how cultural and genetic evolution interact in this framework.

The authors set up their framework using the Price equation from evolutionary biology. The Price equation divides evolutionary change of a trait into two components. The first is a natural selection component resulting from the covariance between a trait and relative fitness. Where there is large covariance, evolution will be fast. Second is a transmission component, which is the fitness-weighted change in trait value between generations (for example, increasing height with improved nutrition across the population would be considered transmission). The Price equation has the neat property that it can be decomposed into within-group and between-group components, allowing analysis in a multilevel selection framework (although not everyone is happy with this decomposition).

But to use this framework, it is important to clarify some terms (which is one of my bugbears about the cultural evolution literature). First, relatedness. As the units of inheritance are cultural traits, the measure of relatedness is similarity in cultural traits. In a simple model where we have one cultural trait, anyone with that same cultural trait has a relatedness of one. In effect, when passing on a cultural trait to another person, they become kin.

The use of the term relatedness is often confusing in the cultural evolution literature as the relatedness of interest is typically genetic relatedness. That is fine, but we need to distinguish the two types of relatedness. Cultural kin are not necessarily genetic kin.

Second, fitness. Cultural fitness reflects the number of people who learn from an individual, plus the degree of influence that they have on those people. Degree of influence is important because, unlike genetic evolution where you have a known and fixed number of ancestors (one parent in the case of asexually reproducing species, two parents for sexually reproducing species such as humans) who contribute a specific amount of genetic material, the number of cultural ancestors may vary by trait and between people. How many people have influenced your cooking? Who was more influential?

Further, for each cultural trait, people will have different fitness. The authors offer the example of Beethoven, whose influence in cookery did not match his influence in music. This necessitates different measurements of cultural fitness for different traits.

Third, generation. The ancestor-descendent relationship is defined by influence, and can have weak relation to biological age. Plato is still spawning direct cultural descendants today, whereas ideas can also spread through a population in days. However, it is only possible to influence people in the next cultural generation, as that is how generation is defined. If I influence someone, they are the next cultural generation in respect of that cultural trait.

Having defined these concepts, they are relatively easy to slot into a cultural Price equation (the maths is in the supplementary information to the paper). While there is extra complexity from considering the degree of influence rather than just the number of descendants, the form of the Price equation is effectively the same for both the genetic and cultural forms. It is just that each deals distinctly with genetic or cultural fitness.

It is also possible to derive a Cultural Hamilton’s Rule. In biology, Hamilton’s rule states that a gene will spread if the cost of the act to the altruist is less than the benefit accrued by the beneficiaries adjusted by the degree of relatedness. A gene can spread if you help kin who also have that gene, even if it comes to a cost to yourself.

Similarly, the Cultural Hamilton’s Rule states that “a behaviour that reduces the actor’s lifetime cultural influence can only be culturally selected for if the cost to him is less than the product of the cultural benefit to his interaction partners and their cultural relatedness to him”. On this point, the authors give an example of two philosophers with the same cultural views. If one chooses to farm to feed the other, allowing the other to focus on spreading the philosophy, the cultural trait may spread despite one of the philosophers effectively sacrificing his own influence.

Under this definition, cultural kin selection becomes a relatively parsimonious explanation for the spread of many cultural traits, such as altruism (and as noted above, this could also be converted into a multilevel selection framework). If people believe in altruism and help others who also do (who are their kin), then helping each other could assist in the further spread of the cultural trait of altruism.

However, this story of spreading cultural altruism falls somewhat short of covering the examples in much of the gene-culture evolution literature. The issue is that, while culture is a part of the model and analysis, people are typically interested in genetic altruism.

Thus, the question of interest is how cultural evolution affects the evolution of genetic altruism? That will be the subject of my next post.

A week of links

Links this week:

  1. Matt Ridley on intelligence and social mobility.
  2. There is a lot to like about this paper: Cultural transmission and the evolution of human behaviour: a general approach based on the Price equation. I’ll post more about it later.
  3. Andrew Gelman on the backlash against replication.
  4. The 15 best behavioural science graphs of 2010 to 2013.


Darwin's Conjecture – Generalising Darwinism

darwinconjectureOver the last couple of months I have been a silent participant in Geoffrey Hodgson and Thorbjørn Knudsen’s reading group for their book Darwin’s Conjecture: The Search for General Principles of Social and Economic Evolution. After finishing the book and following the reading group discussions, I’m not sure I am in a position yet to offer a strong review or critique. But in the meantime, here are some notes about the book.

Hodgson and Knudsen advocate that Darwinism should become the unified evolutionary framework for the social and behavioural sciences. They consider that this has benefits that include establishing the role of variety in the evolution of complex population systems, which economists often aggregate or assume away. It also provides a way of bringing the observed suboptimality prevalent in the natural world into the social context.

To achieve this, they seek to formalise the application of the Darwinian principles. This is the most important contribution of the book. Much of the research on cultural evolution feels, for want of a better word, slippery. When I read works on cultural evolution I often find myself asking what is being replicated? How is it being transmitted? How is it being selected? Is it different from contagion? This is particularly the case where group selection enters the picture. Hodgson and Knudsen tackle these questions by seeking to define what exactly is being replicated and transmitted and accordingly, what is the replicator (the cultural equivalent of the gene) and what is the interactor (the organism or object that natural selection acts upon).

For some chapters, this approach is  useful. The chapter on whether social evolution is Lamarckian (modifications acquired during a lifetime are passed to offspring) is excellent. To assess this claim you need to understand the nature of transmission, which in turn requires definition of the replicator. When and how does the replicator change? Even though I didn’t agree fully agree with their conclusions, their approach allowed a clear assessment of what they were arguing.

Tying down these definitions is not a riskless enterprise, as social evolution does not have a relatively clear entity in “the gene” to select as a replicator. At an individual level, they argue that habits are the appropriate replicator. They prefer habits over memes as they consider it possible to give habits a substrate of biologically inherited instincts, whereas memes are based on habits and instincts and cannot be sustained without them. But why dismiss memes on this basis when they can be given the substrate of habits and instincts (or even a state of the brain) in the same way habits are grounded in biologically inherited instincts? Memes were also attacked on the basis of looseness of terminology, but given the book was designed around formalised Darwinism, why not tighten it? In some respects, I felt as though their discussion on memes was a battle in a long war that I do not know enough about.

Where the authors really started to lose me was when they moved into higher levels of evolution. As is typical when assessing multilevel selection, they noted the Price equation and how it can be used to partition selection at various levels of organisation. But when they laid out their proposed six levels of replicators (genetic, individual, organisational, symbolic, legal, and scientific and technological) across four levels of interactors (individual, organisational, national, scientific and technological organisations), a lot of the crispness of terminology seemed to disappear, along with tools such as the Price equation. The sharpness they brought to the initial chapters of the book faded.

There were a few nice lines in the book.  In dismissing arguments that human intentionality renders analysis of social evolution irrelevant, the authors note that intentionality itself has evolved from similar but less developed attributes among pre-human ancestors. Similarly with artificial selection, it is evolved humans doing the selection

On the flipside, there was also the occasional argument that grated me the wrong way, such as their suggestion that the impulse to produce and acquire in all human societies is a cultural propensity. This is pushing the cultural explanations too far.

Ultimately, the test of their work will be in the application. Although I enjoyed the attempt to tighten the use of some concepts that are often loosely used, it is only when we gain new insights from these tools that the effort will be proved worthwhile. As to whether that is likely to occur, I am not yet convinced (I still have some Steven Pinker like tendencies in this area). I am also reluctant to get sucked into some of the issues in the book as, to my untrained eye, they often appear semantic (as does much of the conversation in the reading group). That is another area where some real-world application will help, with some practical examples to render the material more real.

And as a last word, if you are interested in finding a book as a starting point on cultural evolution, this probably isn’t it. If you have already read a few books in the area, it is worth the effort.

Boyd and Richerson's The Origin and Evolution of Cultures

The Origin and Evolution of CulturesWhen I asked for suggestions for my evolutionary biology and economics reading list earlier this year, Boyd and Richerson’s The Origin and Evolution of Cultures was one of the most recommended. Their exploration of cultural evolution has many elements that are relevant to economics, including the development of institutional frameworks, the evolution of cooperation and the transmission of technology.

The book comprises 20 papers (published between 1987 and 2003) that are grouped into five thematic groups: the evolution of social learning; ethnic groups and markers; human cooperation, reciprocity and group selection; archaeology and culture history; and links to other disciplines. Each chapter was a stand-alone paper, so rather than going into any of them in further detail, I will save that for some later posts and give some more general observations here.

First, Boyd and Richerson are clear in arguing that “culture” is a distinct feature from “environment”, and that it should be examined through an evolutionary lens:

[C]ultural variation is transmitted from individual to individual, it is subject to population dynamic processes analogous to those that effect genetic variation and quite unlike the processes that govern other environmental effects. Combining cultural and environmental effects into a single category conceals these important differences.

Having been sceptical before reading the book, this is one issue on which I am a convert. I am still not convinced that it is always (or often) possible to identify practically which cultural trait is subject to selection or to differentiate it from the environment, but drawing this distinction led to some interesting and parsimonious models. Further, an evolving cultural trait may be the environment for another cultural trait.

Their exploration of cultural evolution often contains a genetic element, usually in the context of “gene-culture coevolution”. For example, they describe a process whereby cultural institutions might result in people with certain genetic predispositions beings weeded out.

Mechanisms by which cultural institutions might exert forces tugging in this direction are not far to seek. People are likely to discriminate against genotypes that are incapable of conforming to cultural norms (Richerson and Boyd, 1989; Laland, Kumm, and Feldman, 1995). People who cannot control their self-serving aggression ended up exiled or executed in small-scale societies and imprisoned in contemporary ones. People whose social skills embarrass their families will have a hard time attracting mates. Of course, selfish and nepotistic impulses were never entirely suppressed; our genetically transmitted evolved psychology shapes human cultures, and, as a result, cultural adaptations often still serve the ancient imperatives of inclusive genetic fitness. However, cultural evolution also creates new selective environments that build cultural imperatives into our genes.

However, Boyd and Richerson’s exploration of gene-culture coevolution does not usually extend to developing models with where genes and culture simultaneously evolve. At times this is problematic, particularly where they incorporate cultural group selection into the picture, as it can be difficult to understand how the process would actually work from the often loose verbal descriptions. Conversely, a model incorporating these multiple evolving elements would lose the clarity and simplicity that allows most of the models in the book to be useful.

The indeterminate nature of the culture-environment distinction I alluded to above is also highlighted by this gene-culture evolution quote. Cultural evolution creates new selective environments. While a cultural trait is evolving, it is effectively creating an environment in which other cultural traits or genes evolve. This is similar to the idea that genes effectively create the environment in which other genes evolve, whether those other genes be in the same individual or in other individuals and species.

Boyd and Richerson’s work shares some similarity with that of Sam Bowles and Herb Gintis, particularly in their approach to model development. Simulations are used as illustrations, the focus is more on demonstrating ideas than providing hard proofs, and agent based models are a common tool.  However, Boyd and Richerson have a stronger sense than Bowles and Gintis of the limitations of their models, and generally recognise their illustrative and not determinative nature. Bowles and Gintis have a habit of making a model and arguing that, since a certain feature didn’t work in their model (such as the evolution of cooperation by reciprocal altruism), their model is evidence that it can’t work at all. The problem with this approach is that the model only examines such a small subspace of the possibilities. Boyd and Richerson tend to be more constrained in their conclusions, although not always so.

One of the groups of papers focuses on group selection. I am more open to analysing the transmission of cultural traits through the lens of group selection (or multilevel selection) than I am for the transmission of genes, largely because cultural group selection is not necessarily undermined by migration between groups in the same way as genetic group selection. Boyd and Richerson note this when they state:

[S]ocial extinction does not mean physical elimination of the entire group. Quite the contrary, most people survive defeat but flee as refugees to other groups, into which they are incorporated. This sort of extinction cannot support genetic group selection because so many of the defeated survive and because they would tend to carry their unsuccessful genes into successful groups, rapidly running down variation between groups. However, the effects of conformist cultural transmission combined with moralistic punishment makes between-group cultural variation much less subject to erosion by migration and within-group success of uncooperative strategies than is true in the case of acultural organisms.

However, I am still not convinced that the cultural group selection approach provides the clearest method of analysis. I’ll save my specific issues with their approach in a separate post.

My favourite chapter of the book was the least theoretical. Boyd and Richerson (with Joseph Soltis) asked whether observed rates of group extinction could be sufficient for group selection to drive rapid cultural evolution. Based on an examination of hunter-gather tribe extinction rates, they concluded that group selection could not be responsible. It was refreshing to see some empirical analysis applied to this issue. For all the noise around group selection (both genetic and cultural), it is rare that the debates are accompanied by increasingly available data.

*My later post with my thoughts on their approach to group selection can be found here.

Henrich on markets, trust and monogamy

The Edge has put up video and transcript of a great interview with Joe Henrich (the Canada Research Chair in Culture, Cognition and Evolution at UBC). The whole interview is worth watching or reading.

A couple of the more interesting snippets are below. First, on the division of labour:

One of the interesting things about the division of labor is that you’re not going to specialize in a particular trade—maybe you make steel plows—unless you know that there are other people who are specializing in other kinds of trades which you need—say food or say materials for making housing, and you have to be confident that you can trade with them or exchange with them and get the other things you need. There’s a lot of risk in developing specialization because you have to be confident that there’s a market there that you can engage with. Whereas if you’re a generalist and you do a little bit of farming, a little bit of manufacturing, then you’re much less reliant on the market. Markets require a great deal of trust and a great deal of cooperation to work. Sometimes you get the impression from economics that markets are for self-interested individuals. They’re actually the opposite. Self-interested individuals don’t specialize, and they don’t take it [to market], because there’s all this trust and fairness that are required to make markets run with impersonal others.

I don’t agree with Heinrich’s use of the word self-interested in the last sentence, as being trusting, specialising and trading has large individual benefits. However, the importance of trust is rarely emphasised enough.

Second, on monogamy:

Societies that have this are better able to maintain a harmonious population, increase trade and exchange, and have economic growth more than societies that allow polygamy, especially if you have a society with widely varying amounts of wealth, especially among males. Then you’re going to have a situation that would normally promote high levels of polygyny. The absolute levels of wealth difference of, say, between Bill Gates and Donald Trump and the billionaires of the world, and the men at the bottom end of the spectrum is much larger than it’s ever been in human history, and that includes kings and emperors and things like that in terms of total control of absolute wealth. Males will be males in the sense that they’ll try to obtain extra matings, but the billionaires are completely curbed in terms of what they would do if they could do what emperors have done throughout the ages. They have harems and stuff like that. Norms of modern society prevent that.

Otherwise, there would be massive male-male competition, and even to get into the mating and marriage market you would have to have a high level of wealth if we were to let nature take it’s course as it did in the earliest empires. It depends on what your views are about freedom versus societal level benefits.

The nature of the causative link between monogamy and economic growth is an interesting question. Monogamy promotes stability, but I suspect that populations that implement monogamy are the same populations likely to implement a range of other growth promoting institutions.

I also tend to see the tradeoff between the freedom of polygamy and the “societal level benefits” of monogamy as being an indirect tradeoff. If a few men monopolised all the women, they would quickly find their freedom curtailed by the other men.

The interview has plenty of other interesting food for thought.

The evolution of cornets

In my recent review of Paul Ormerod’s Why Most Things Fail, I asked if Ormerod’s comparison between the extinction of species and the death of firms was the right analogy. One reason for my question was that species are typically defined due to their reproductive isolation, preventing gene transfer between species. In contrast, the unit of selection for firms, business plan modules (the name used by Eric Beinhocker), can spread freely spread between firms.

Interestingly, I have just picked up Kevin Kelly’s What Technology Wants, 18 months after my post speculating on Kelly’s approach, where he raises a similar issue. Kelly notes that whereas the passage of biological traits is limited to the passing of traits to offspring, technology transmission can occur horizontally. He writes:

[N]ature can’t plan ahead. It does not hoard innovations for later use. If a variation in nature does not provide an immediate survival advantage, it is too costly to maintain and so over time it disappears. But sometimes a trait advantageous for one problem will turn out to be advantageous for a second, unanticipated problem. … These inadvertent anticipatory inventions are called exaptations in biology. We don’t know how common exaptations are in nature, but they are routine in the technium. The technium is nothing but exaptations, since innovations can be easily borrowed across lines of origin or moved across time and repurposed.

Niles Eldredge is the cofounder (with Stephen Jay Gould) of the theory of punctuated, stepwise evolution. … Once Eldredge applied his professional taxonomic methods to his collection of 500 cornets, some dating back to 1825. He selected 17 traits that varied among his instruments—the shape of their horns, the placement of the valves, the length and diameter of their tubes—very similar to the kinds of metrics he applies to trilobites. When he mapped the evolution of cornets using techniques similar to those he applies to ancient arthropods, he found that the pattern of the lineages were very similar in many ways to those of living organisms. As one example, the evolution of cornets showed a stepwise progress, much like trilobites. But the evolution of musical instruments was also very distinctive. The key difference between the evolution of multicellular life and the evolution of the technium is that in life most blending of traits happens “vertically” in time. Innovations are passed from living parents down (vertically) through offspring. In the technium, on the other hand, most blending of traits happens laterally across time—even from “extinct” species and across lineages from nonparents. Eldredge discovered that the pattern of evolution in the technium is not the repeated forking of branches we associate with the tree of life, but rather a spreading, recursive network of pathways that often double back to “dead” ideas and resurrect “lost” traits.

Kelly goes as far as suggesting that no species of technology ever goes extinct. I’m not sure that calling a technology a species is the right approach – is the species the horn and the feature of the horn the unit of selection? – but the general point has some significant consequences for the biology-technology analogy. Similarly, the firm-species analogy is not a perfect fit due to this horizontal transfer of business plan modules, and possibility that individual modules never go extinct. In the case of Ormerod’s analysis however, I’m not yet sure what the consequences of that difference is.

The article by Tëmkin and Eldredge that charts the evolution of cornets can be found in Current Anthropology (ungated version here).