A two level mutation-selection model of cultural evolution and diversity

Cultural evolution is a complex process that can happen at several levels. At the level of individuals in a population, each human bears a set of cultural traits that he or she can transmit to its offspring (vertical transmission) or to other members of his or her society (horizontal transmission). The relative frequency of a cultural trait in a population or society can thus increase or decrease with the relative reproductive success of its bearers (individual’s level) or the relative success of transmission (called the idea’s level). This article presents a mathematical model on the interplay between these two levels. The first aim of this article is to explore when cultural evolution is driven by the idea’s level, when it is driven by the individual’s level and when it is driven by both. These three possibilities are explored in relation to (a) the amount of interchange of cultural traits between individuals, (b) the selective pressure acting on individuals, (c) the rate of production of new cultural traits, (d) the individual’s capacity to remember cultural traits and to the population size. The aim is to explore the conditions in which cultural evolution does not lead to a better adaptation of individuals to the environment. This is to contrast the spread of fitness-enhancing ideas, which make individual bearers better adapted to the environment, to the spread of “selfish” ideas, which spread well simply because they are easy to remember but do not help their individual bearers (and may even hurt them). At the same time this article explores in which conditions the adaptation of individuals is maximal. The second aim is to explore how these factors affect cultural diversity, or the amount of different cultural traits in a population. This study suggests that a larger interchange of cultural traits between populations could lead to cultural evolution not improving the adaptation of individuals to their environment and to a decrease of cultural diversity.     

The problem of adaptive individual choice in cultural evolution

This paper tries to explain how individuals manage adaptive individual choice (i.e., the decision to acquire a fitter than average behavior or idea rapidly and tractably) in cultural evolution, despite the fact that acquiring fitness information is very difficult. I argue that the means of solving this problem suggested in the cultural evolution literature largely are various types of decision rules employing representations of fitness correlated properties or states of affairs. I argue that the problem of adaptive individual choice is best solved where some of these learning rule representations are socially transmitted and some are biologically transmitted.

Detecting wholesale copying in cultural evolution

A cultural practice can spread because it is transmitted with high fidelity, but also because biased transformation leads to its reinvention. The respective effect of these two mechanisms, however, may only be quantified if we can measure and detect high-fidelity transmission. This paper proposes wholesale copying, the reproduction of a set of elements as a set, as an operational definition. Using two corpus of heraldic designs (total n = 13,453), we apply information-theoretic tools to detect cases of wholesale copying and gauge their incidence. Heraldic designs are composed according to rigorous combinatorial rules. Wholesale copying causes the frequency of a design to increase out of proportion with the frequency of the motif and tinctures that make it up. Comparing the frequency of designs with that of their component motifs and tinctures, we show that the amount of information carried by a design tracks its inheritance along family lines. A model predicting the frequency of heraldic designs based solely on the frequency of their component parts systematically outperforms one that assumes a mix of wholesale copying and random mutation (with realistic mutation rates). These findings are consistent with low but non-null incidences of wholesale copying in the diffusion of heraldic designs.     

Mating games: cultural evolution and sexual selection

In this paper, we argue that mating games, a concept that denotes cultural practices characterized by a competitive element and an ornamental character, are essential drivers behind the emergence and maintenance of human cultural practices. In order to substantiate this claim, we sketch out the essential role of the game’s players and audience, as well as the ways in which games can mature and turn into relatively stable cultural practices. After outlining the life phase of mating games – their emergence, rise, maturation, and possible eventual decline – we go on to argue that participation in these games (in each phase) does make sense from an adaptationist point of view. The strong version of our theory which proposes that all cultural practices are, or once were, mating games, allows us to derive a set of testable predictions for the fields of archaeology, economics, and psychology.     

Experimental models for testing hypotheses about cumulative cultural evolution

The rapid appearance (over evolutionary time) of the cognitive skills and complex inventions of modern humans has been attributed to “cumulative cultural evolution” (CCE), the accumulation of knowledge and skills over generations. To date, researchers have only been able to speculate about the reasons for the apparent absence of this phenomenon in nonhumans, and it has not been possible to test hypotheses regarding the mechanisms underlying it. Here, we show that it is possible to demonstrate CCE under laboratory conditions by simulating generational succession through the repeated removal and replacement of human participants within experimental groups. We created “microsocieties” in which participants were instructed to complete simple tasks using everyday materials. In one of our procedures, participants were instructed to build a paper aeroplane which flew as far as possible, and in the other, they were instructed to construct a tower of spaghetti which was as tall as possible. We show that, in both cases, information accumulates within the groups such that later generations produce designs which are more successful than earlier ones. These methods offer researchers a window to understanding CCE, allowing for experimental manipulation and hypothesis testing.     

Natural selection in chemical evolution

We propose that chemical evolution can take place by natural selection if a geophysical process is capable of heterotrophic formation of liposomes that grow at some base rate, divide by external agitation, and are subject to stochastic chemical avalanches, in the absence of nucleotides or any monomers capable of modular heredity. We model this process using a simple hill-climbing algorithm, and an artificial chemistry that is unique in exhibiting conservation of mass and energy in an open thermodynamic system. Selection at the liposome level results in the stabilization of rarely occurring molecular autocatalysts that either catalyse or are consumed in reactions that confer liposome level fitness; typically they contribute in parallel to an increasingly conserved intermediary metabolism. Loss of competing autocatalysts can sometimes be adaptive. Steady-state energy flux by the individual increases due to the energetic demands of growth, but also of memory, i.e. maintaining variations in the chemical network. Self-organizing principles such as those proposed by Kauffman, Fontana, and Morowitz have been hypothesized as an ordering principle in chemical evolution, rather than chemical evolution by natural selection. We reject those notions as either logically flawed or at best insufficient in the absence of natural selection. Finally, a finite population model without elitism shows the practical evolutionary constraints for achieving chemical evolution by natural selection in the lab.     

The evolution of social learning rules: Payoff-biased and frequency-dependent biased transmission

Humans and other animals do not use social learning indiscriminately, rather, natural selection has favoured the evolution of social learning rules that make selective use of social learning to acquire relevant information in a changing environment. We present a gene-culture coevolutionary analysis of a small selection of such rules (unbiased social learning, payoff-biased social learning and frequency-dependent biased social learning, including conformism and anti-conformism) in a population of asocial learners where the environment is subject to a constant probability of change to a novel state. We define conditions under which each rule evolves to a genetically polymorphic equilibrium. We find that payoff-biased social learning may evolve under high levels of environmental variation if the fitness benefit associated with the acquired behaviour is either high or low but not of intermediate value. In contrast, both conformist and anti-conformist biases can become fixed when environment variation is low, whereupon the mean fitness in the population is higher than for a population of asocial learners. Our examination of the population dynamics reveals stable limit cycles under conformist and anti-conformist biases and some highly complex dynamics including chaos. Anti-conformists can out-compete conformists when conditions favour a low equilibrium frequency of the learned behaviour. We conclude that evolution, punctuated by the repeated successful invasion of different social learning rules, should continuously favour a reduction in the equilibrium frequency of asocial learning, and propose that, among competing social learning rules, the dominant rule will be the one that can persist with the lowest frequency of asocial learning.     

The history of Hayek’s theory of cultural evolution

This paper traces the historical origins of Friedrich A. Hayek’s theory of cultural evolution, and argues that Hayek’s evolutionary thought was significantly inspired by Alexander M. Carr-Saunders and Oxford zoology. While traditional Hayek scholarship emphasizes the influence of Carl Menger and the British eighteenth-century moral philosophers, I claim that these sources underdetermine what was most characteristic of Hayek’s theory, viz. the idea that cultural evolution is a matter of group selection, and the idea that natural selection operates on acquired as well as on inherited properties.     

The sky is falling: evidence of a negativity bias in the social transmission of information

The method of serial reproduction has revealed that the social transmission of information is characterized by the gradual transformation of the original message. This transformation results from the preferential survival of certain types of information and the resolution of ambiguity. Here we present evidence of a bias favoring the social transmission of negatively-valenced information across multiple transmission episodes. Ninety-two, four-person chains transmitted a story containing unambiguously positive and unambiguously negative story events, along with ambiguous story events that could be interpreted positively or negatively. Analysis using mixed-effects modeling revealed the preferential survival of unambiguously negative events over positive events, and the increasingly negative resolution of ambiguous events across successive transmission episodes. Contrary to predictions, elevated state anxiety did not enhance the social transmission of negatively-valenced information. We also found that the survival of unambiguously negative story events was positively correlated with the negative resolution of ambiguous story events, reflecting a general negativity-bias in the social transmission of information.     

Fertility selection,genetic selection and evolution

The relationship between fertility selection as measured by the correlation in progeny number between parents and offspring, and selection at individual loci is investigated in humans. Estimates for the magnitude of fertility selection (0.1) and the rate of gene substitution (0.5 gene substitutions per generation per genome) are used in various mathematical models for selection. It is found that the observed magnitude of fertility selection cannot be explained by non‐epistatic directional selection at individual loci. A symmetric quantitative directional selection model is consistent with the observed data. But it is possible that fertility selection does not have a genetic basis.     

Variability selection in hominid evolution

Variability selection (abbreviated as VS) is a process considered to link adaptive change to large degrees of environment variability. Its application to hominid evolution is based, in part, on the pronounced rise in environmental remodeling that took place over the past several million years. The VS hypothesis differs from prior views of hominid evolution, which stress the consistent selective effects associated with specific habitats or directional trends (e.g., woodland, savanna expansion, cooling). According to the VS hypothesis, wide fluctuations over time created a growing disparity in adaptive conditions. Inconsistency in selection eventually caused habitat-specific adaptations to be replaced by structures and behaviors responsive to complex environmental change. Key hominid adaptations, in fact, emerged during times of heightened variability. Early bipedality, encephalized brains, and complex human sociality appear to signify a sequence of VS adaptations—i.e., a ratcheting up of versatility and responsiveness to novel environments experienced over the past 6 million years. The adaptive results of VS cannot be extrapolated from selection within a single environmental shift or relatively stable habitat. If some complex traits indeed require disparities in adaptive setting (and relative fitness) in order to evolve, the VS idea counters the prevailing view that adaptive change necessitates long-term, directional consistency in selection. © 1998 Wiley-Liss, Inc.     

Foresight in cultural evolution

Critics of Darwinian cultural evolution frequently assert that whereas biological evolution is blind and undirected, cultural change is directed or guided by people who possess foresight, thereby invalidating any Darwinian analysis of culture. Here I show this argument to be erroneous and unsupported in several respects. First, critics commonly conflate human foresight with supernatural clairvoyance, resulting in the premature rejection of Darwinian cultural evolution on false logical grounds. Second, the presence of foresight is perfectly consistent with Darwinian evolution, and is found in biology, in the form of open, teleonomic processes such as genetically-biased behavioural learning. Finally, empirical evidence from the social sciences suggests that cultural change appears far less guided and directed, and human foresight far less accurate, than is commonly assumed.

Natural selection in the <Emphasis Type="Italic">TLR-</Emphasis>related genes in the course of primate evolution

The innate immune system constitutes the front line of host defense against pathogens. Toll-like receptors (TLRs) recognize molecules derived from pathogens and play crucial roles in the innate immune system. Here, we provide evidence that the TLR-related genes have come under natural selection pressure in the course of primate evolution. We compared the nucleotide sequences of 16 TLR-related genes, including TLRs (TLR1–10), MYD88, TILAP, TICAM1, TICAM2, MD2, and CD14, among seven primate species. Analysis of the non-synonymous/synonymous substitution ratio revealed the presence of both strictly conserved and rapidly evolving regions in the TLR-related genes. The genomic segments encoding the intracellular Toll/interleukin 1 receptor domains, which exhibited lower rates of non-synonymous substitution, have undergone purifying selection. In contrast, TLR4, which carried a high proportion of non-synonymous substitutions in the part of extracellular domain spanning 200 amino acids, was found to have been the suggestive target of positive Darwinian selection in primate evolution. However, sequence analyses from 25 primate species, including eight hominoids, six Old World monkeys, eight New World monkeys, and three prosimians, showed no evidence that the pressure of positive Darwinian selection has shaped the pattern of sequence variations in TLR4 among New World monkeys and prosimians. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Questioning the cultural evolution of altruism

The evolutionary foundations of helping among nonkin in humans have been the object of intense debates in the past decades. One thesis has had a prominent influence in this debate: the suggestion that genuine altruism, strictly defined as a form of help that comes at a net fitness cost for the benefactor, might have evolved owing to cultural transmission. The gene–culture coevolution literature is wont to claim that cultural evolution changes the selective pressures that normally act to limit the emergence of altruistic behaviours. This paper aims to recall, however, that cultural transmission yields altruism only to the extent that it relies on maladaptive mechanisms, such as conformist imitation and (in some cases) payoff‐biased transmission. This point is sometimes obscured in the literature by a confusion between genuine altruism, maladaptive by definition, and mutualistic forms of cooperation, that benefit all parties in the long run. Theories of cultural altruism do not lift the selective pressures weighing on strictly altruistic actions; they merely shift the burden of maladaptation from social cognition to cultural transmission.     

Natural selection and social preferences

A large number of individuals are randomly matched into groups, where each group plays a finite symmetric game. Individuals breed true. The expected number of surviving offspring depends on own material payoff, but may also, due to cooperative breeding and/or reproductive competition, depend on the material payoffs to other group members. The induced population dynamic is equivalent with the replicator dynamic for a game with payoffs derived from those in the original game. We apply this selection dynamic to a number of examples, including prisoners' dilemma games with and without a punishment option, coordination games, and hawk-dove games. For each of these, we compare the outcomes with those obtained under the standard replicator dynamic. By way of a revealed-preference argument, our selection dynamic can explain certain "altruistic" and "spiteful" behaviors that are consistent with individuals having social preferences.     

The evolution of cultural evolution

Humans are unique in their range of environments and in the nature and diversity of their behavioral adaptations. While a variety of local genetic adaptations exist within our species, it seems certain that the same basic genetic endowment produces arctic foraging, tropical horticulture, and desert pastoralism, a constellation that represents a greater range of subsistence behavior than the rest of the Primate Order combined. The behavioral adaptations that explain the immense success of our species are cultural in the sense that they are transmitted among individuals by social learning and have accumulated over generations. Understanding how and when such culturally evolved adaptations arise requires understanding of both the evolution of the psychological mechanisms that underlie human social learning and the evolutionary (population) dynamics of cultural systems.     

Convergent evolution of Darwin's finches caused by introgressive hybridization and selection

Abstract Between 1973 and 2003 mean morphological features of the cactus finch, Geospiza scandens, and the medium ground finch, G. fortis, populations on the Galápagos island of Daphne Major were subject to fluctuating directional selection. An increase in bluntness or robustness in the beak of G. scandens after 1990 can only partly be explained by selection. We use 16 microsatellite loci to test predictions of the previously proposed hypothesis that introgressive hybridization contributed to the trend, resulting in genes flowing predominantly from G. fortis to G. scandens. To identify F₁ hybrids and backcrosses we use pedigrees where known, supplemented by the results of assignment tests based on 14 autosomal loci when parents were not known. We analyze changes in morphology and allelic composition in the two populations over a period of 15–20 years. With samples that included F₁ hybrids and backcrosses, the G. scandens population became more similar to the G. fortis population both genetically and morphologically. Gene flow between species was estimated to be three times greater from G. fortis to G. scandens than in the opposite direction, resulting in a 20% reduction in the genetic difference between the species. Nevertheless, removing identified F₁ hybrids and backcrosses from the total sample and reanalyzing the traits did not eliminate the convergence. The two species also converged in beak shape by 22.2% and in body size by 45.5%. A combination of introgressive hybridization and selection jointly provide the best explanation of convergence in morphology and genetic constitution under the changed ecological conditions following a major El Niño event in 1983. The study illustrates how species without postmating barriers to gene exchange can alternate between convergence and divergence when environmental conditions oscillate.     

Success-biased social learning: Cultural and evolutionary dynamics

Success bias is a social learning strategy whereby learners tend to acquire the cultural variants of successful individuals. I develop a general model of success-biased social learning for discrete cultural traits with stochastic payoffs, and investigate its dynamics when only two variants are present. I find that success bias inherently favors rare variants, and consequently performs worse than unbiased imitation (i.e. random copying) when success payoffs are at least mildly stochastic and the optimal variant is common. Because of this weakness, success bias fails to replace unbiased imitation in an evolutionary model when selection is fairly weak or when the environment is relatively stable, and sometimes fails to invade at all. I briefly discuss the optimal strength of success bias, the complicated nature of defining success in social learning contexts, and the value of variant frequency as an important source of information to social learners. I conclude with predictions regarding the prevalence of success bias in different behavioral domains.