Human cultural traits—behaviors, ideas, and technologies that can be learned from other individuals—can exhibit complex patterns of transmission and evolution, and researchers have developed theoretical models, both verbal and mathematical, to facilitate our understanding of these patterns. Many of the first quantitative models of cultural evolution were modified from existing concepts in theoretical population genetics because cultural evolution has many parallels with, as well as clear differences from, genetic evolution. Furthermore, cultural and genetic evolution can interact with one another and influence both transmission and selection. This interaction requires theoretical treatments of gene–culture coevolution and dual inheritance, in addition to purely cultural evolution. In addition, cultural evolutionary theory is a natural component of studies in demography, human ecology, and many other disciplines. Here, we review the core concepts in cultural evolutionary theory as they pertain to the extension of biology through culture, focusing on cultural evolutionary applications in population genetics, ecology, and demography. For each of these disciplines, we review the theoretical literature and highlight relevant empirical studies. We also discuss the societal implications of the study of cultural evolution and of the interactions of humans with one another and with their environment.

Significance: The archaeological record suggests that cultural traits, as manifested in the tool repertoire, can accumulate exponentially, that technology can appear in bursts after long periods of stasis, and that dramatic cultural losses can occur. We introduce a model that accounts for this range of observations by considering a multifaceted creative process of innovation, accounting for the possibility that certain traits facilitate the invention of related traits. Further, we determine that differential distribution of tool-related knowledge, typically ignored in models, can dramatically affect the dynamics of cultural evolution, suggesting the concept of an effective cultural population size. Finally, we demonstrate that a fluctuating environment can lead to large-scale cultural losses and select for generalist tools that are useful in multiple conditions.

Host-associated microbiomes influence their host's fitness in myriad ways and can be viewed as a source of phenotypic plasticity. This plasticity may allow the host to accommodate novel environmental challenges and thus influence the host's evolutionary adaptation. As with other modalities of phenotypic plasticity in phenomena such as the Baldwin effect and genetic assimilation, the microbiome-mediated plasticity may influence host genetic adaptation by facilitating and accelerating it, by slowing it down, or even by preventing it. The dynamics involved are likely more complex than those of previously studied phenomena related to phenotypic plasticity, and involve different processes on each time scale, such as acquired recognition of newly associated microbes by the host's immune system on single- and multiple-generation time scales, or selection on transmission dynamics of microbes between hosts, acting on longer time scales. To date, it is unclear if and how any of these processes shape host evolution. This opinion piece article provides a conceptual framework for considering the processes by which microbiome-mediated plasticity directs host evolution and concludes with suggestions for key experimental tests of the presented ideas. This article is part of the theme issue ‘The role of the microbiome in host evolution’.

In Drosophila, multiple lines of evidence converge in suggesting that beneficial substitutions to the genome may be common. All suffer from confounding factors, however, such that the interpretation of the evidence—in particular, conclusions about the rate and strength of beneficial substitutions—remains tentative. Here, we use genome-wide polymorphism data in D. simulans and sequenced genomes of its close relatives to construct a readily interpretable characterization of the effects of positive selection: the shape of average neutral diversity around amino acid substitutions. As expected under recurrent selective sweeps, we find a trough in diversity levels around amino acid but not around synonymous substitutions, a distinctive pattern that is not expected under alternative models. This characterization is richer than previous approaches, which relied on limited summaries of the data (e.g., the slope of a scatter plot), and relates to underlying selection parameters in a straightforward way, allowing us to make more reliable inferences about the prevalence and strength of adaptation. Specifically, we develop a coalescent-based model for the shape of the entire curve and use it to infer adaptive parameters by maximum likelihood. Our inference suggests that ∼13% of amino acid substitutions cause selective sweeps. Interestingly, it reveals two classes of beneficial fixations: a minority (approximately 3%) that appears to have had large selective effects and accounts for most of the reduction in diversity, and the remaining 10%, which seem to have had very weak selective effects. These estimates therefore help to reconcile the apparent conflict among previously published estimates of the strength of selection. More generally, our findings provide unequivocal evidence for strongly beneficial substitutions in Drosophila and illustrate how the rapidly accumulating genome-wide data can be leveraged to address enduring questions about the genetic basis of adaptation. Characterizing the nature of beneficial changes to the genome is essential to our understanding of adaptation. To do so, researchers identify and analyze footprints that beneficial changes leave in patterns of genetic variation within and between species. In order to teach us about adaptive evolution, these footprints need to be specific to positive selection as well as rich enough to allow for reliable inferences. Here, we identify such a footprint: a pronounced trough in the average levels of genetic diversity surrounding amino acid substitutions throughout the D. simulans genome. Based on this pattern, we infer that approximately 13% of amino acid substitutions were beneficial, a minority of which (3%) conferred a large selective advantage of nearly 0.5% and the majority of which (10%) conferred a much smaller advantage of about 0.01%. These findings offer insights into the distribution of selection effects driving beneficial changes to the D. simulans genome and suggest how the widely varying estimates obtained in previous studies of Drosophila may be reconciled. Moreover, the approach that we introduce is readily applicable to other taxa and thus should help to gain important insights into how the rate and strength of adaptive evolution vary depending on life-history, population size, and ecology.

Evidence for interactions between populations plays a prominent role in the reconstruction of historical and prehistoric human dynamics; these interactions are usually interpreted to reflect cultural practices or demographic processes. The sharp increase in long-distance transportation of lithic material between the Middle and Upper Palaeolithic, for example, is seen as a manifestation of the cultural revolution that defined the transition between these epochs. Here, we propose that population interaction is not only a reflection of cultural change but also a potential driver of it. We explore the possible effects of inter-population migration on cultural evolution when migrating individuals possess core technological knowledge from their original population. Using a computational framework of cultural evolution that incorporates realistic aspects of human innovation processes, we show that migration can lead to a range of outcomes, including punctuated but transient increases in cultural complexity, an increase of cultural complexity to an elevated steady state and the emergence of a positive feedback loop that drives ongoing acceleration in cultural accumulation. Our findings suggest that population contact may have played a crucial role in the evolution of hominin cultures and propose explanations for observations of Palaeolithic cultural change whose interpretations have been hotly debated.