Interactions of genetic and cultural evolution: Models and examples

This paper proposes models and examples of five principal modes of interaction between genes and culture in human evolution. Because genes and culture ultimately interact in the minds of individuals, the models are focused on individual level processes of constrained microevolution. The central hypotheses are (1) that cultural evolution as well as genetic evolution commonly proceeds by the differential transmission of alternative instructions among individuals, (2) that genetic and cultural processes directly interact through mutual influence on each other's differentials of transmission in a population, (3) that the cultural process is often self-selecting by its own criteria, and (4) that these criteria generally operate to enhance rather than oppose human adaptation. Evolutionary change at higher levels, which is particularly important in sociocultural evolution, is interpreted as restructuring the nature and extent of the variability available at the individual level. To clarify the conceptual differences of the models and hopefully to stimulate related analyses in other areas, I discuss selected examples of each of these interactions. I conclude with some remarks on the relative importance of the models to human ecology and evolution.     

Spectacular phenomena and limits to rationality in genetic and cultural evolution

In studies of both animal and human behaviour, game theory is used as a tool for understanding strategies that appear in interactions between individuals. Game theory focuses on adaptive behaviour, which can be attained only at evolutionary equilibrium. We suggest that behaviour appearing during interactions is often outside the scope of such analysis. In many types of interaction, conflicts of interest exist between players, fuelling the evolution of manipulative strategies. Such strategies evolve out of equilibrium, commonly appearing as spectacular morphology or behaviour with obscure meaning, to which other players may react in non-adaptive, irrational ways. We present a simple model to show some limitations of the game-theory approach, and outline the conditions in which evolutionary equilibria cannot be maintained. Evidence from studies of biological interactions seems to support the view that behaviour is often not at equilibrium. This also appears to be the case for many human cultural traits, which have spread rapidly despite the fact that they have a negative influence on reproduction.     

Downhill protein folding: evolution meets physics

Proteins can be redesigned to fold downhill on a free energy surface characterized by only a few coordinates, confirming a principal prediction of the 'energy-landscape' model. Nonetheless, natural proteins have small but significant barriers. Spectroscopy and kinetics reveal potential biological causes for activation barriers during protein folding: evolution against protein aggregation and for protein function.     

Brassicaceae phylogeny and trichome evolution

To estimate the evolutionary history of the mustard family (Brassicaceae or Cruciferae), we sampled 113 species, representing 101 of the roughly 350 genera and 17 of the 19 tribes of the family, for the chloroplast gene ndhF. The included accessions increase the number of genera sampled over previous phylogenetic studies by four-fold. Using parsimony, likelihood, and Bayesian methods, we reconstructed the phylogeny of the gene and used the Shimodaira-Hasegawa test (S-H test) to compare the phylogenetic results with the most recent tribal classification for the family. The resultant phylogeny allowed a critical assessment of variations in fruit morphology and seed anatomy, upon which the current classification is based. We also used the S-H test to examine the utility of trichome branching patterns for describing monophyletic groups in the ndhF phylogeny. Our phylogenetic results indicate that 97 of 114 ingroup accessions fall into one of 21 strongly supported clades. Some of these clades can themselves be grouped into strongly to moderately supported monophyletic groups. One of these lineages is a novel grouping overlooked in previous phylogenetic studies. Results comparing 30 different scenarios of evolution by the S-H test indicate that five of 12 tribes represented by two or more genera in the study are clearly polyphyletic, although a few tribes are not sampled well enough to establish para- or polyphyly. In addition, branched trichomes likely evolved independently several times in the Brassicaceae, although malpighiaceous and stellate trichomes may each have a single origin.     

Apolipoprotein E phylogeny and evolution

Among apolipoproteins, apolipoprotein E (Apo E) plays a pivotal role in lipid transport and is proposed to be involved in neural repair. Because of a long divergence history of apolipoproteins, it is unclear how Apo E evolved in time. To investigate relationships among Apo E proteins, we used the information from molecular data and analysed the phylogeny of Apo E proteins from various species. Several phylogenetic trees were generated by using both character-based and distance-based phylogenetic methods. Apo E sequences of fish and frog were found to be less related to the Apo E sequences of other species. The most likely ancestor of Apo E among 18 organisms was estimated to be the Apo E of frog. Members of the groups formed by the Apo E proteins of various species shared similar feeding habits and diet. It may be suggested that Apo E evolution and very likely the evolution of other apolipoproteins are influenced by the organism's feeding environment and diet.     

The genetic implications of biological and cultural structuring processes during hominid evolution

Human populations are genetically structured through biological reproduction but reproduction is socially structured through culturally expressed systems of marriage, hence the need to take into account the cultural dimension of human societies when considering the genetic structure of modern human populations. The interplay between these two structuring processes is examined through the implications of a biologically based primate form of social organization versus a culturally based foraging form of social organization for an anomaly between the genetic differentiation implied by micro-evolutionary genetic models versus the species-wide pattern of morphological change implied by hominid fossil evidence. Simulation is used to derive the pattern for genetic differentiation at the level of the living group for both forms of social organization and a competition model is added to the genetic model as a way to resolve the anomaly. The importance of the competition model for the transition from a biologically based to a culturally based form of social organization is discussed.     

Homicide and cultural evolution

Homicide rates are suitable materials for the study of “cultural evolution,” because they vary dramatically between societies (hence, are “cultural”) and change gradually rather than saccadically (hence, “evolve”).Sociological models of the sources of variation in homicide rates (“subcultures of violence”; demographic change; “legitimation of violence”; mass media effects) are criticized for inattention to the social context of violence and to the individual motives of the protagonists. Models of culture change that emphasize “transmission” are criticized for treating the culture-bearing person as a passive vessel rather than an active strategist. A satisfactory theory of the “cultural evolution” of violence awaits satisfactory theories of how people apprehend their interests and how they pursue them.     

When phylogeny meets geology and chemistry: doubts on the dating of Ethiopian amber

The first fossil species of a Melissotarsus ant is described (Melissotarsus ethiopiensis n. sp.), suggesting that Ethiopian amber could be cenozoic rather than cretaceous. This hypothesis is supported by a Fourier transform infrared spectroscopy (FTIR) analysis of the amber itself, suggesting a weak maturation of the fossil resin, and a revision of the pyrolysis–gas chromatography–mass spectrometry (PY-GC-MS) analysis done by Schmidt and his collaborators in 2010, in an article in which the deposit was described for the first time.     

Mammalian evolution and biomedicine: new views from phylogeny

Recent progress resolving the phylogenetic relationships of the major lineages of mammals has had a broad impact in evolutionary biology, comparative genomics and the biomedical sciences. Novel insights into the timing and historical biogeography of early mammalian diversification have resulted from a new molecular tree for placental mammals coupled with dating approaches that relax the assumption of the molecular clock. We highlight the numerous applications to come from a well-resolved phylogeny and genomic prospecting in multiple lineages of mammals, from identifying regulatory elements in mammalian genomes to assessing the functional consequences of mutations in human disease loci and those driving adaptive evolution.     

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.     

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.     

Going nuclear: gene family evolution and vertebrate phylogeny reconciled

Gene duplications have been common throughout vertebrate evolution, introducing paralogy and so complicating phylogenetic inference from nuclear genes. Reconciled trees are one method capable of dealing with paralogy, using the relationship between a gene phylogeny and the phylogeny of the organisms containing those genes to identify gene duplication events. This allows us to infer phylogenies from gene families containing both orthologous and paralogous copies. Vertebrate phylogeny is well understood from morphological and palaeontological data, but studies using mitochondrial sequence data have failed to reproduce this classical view. Reconciled tree analysis of a database of 118 vertebrate gene families supports a largely classical vertebrate phylogeny.     

Cumulative cultural evolution and demography

The idea that demographic change may spur or slow down technological change has become widely accepted among evolutionary archaeologists and anthropologists. Two models have been particularly influential in promoting this idea: a mathematical model by Joseph Henrich, developed to explain the Tasmanian loss of culture during the Holocene; and an agent-based adaptation thereof, devised by Powell et al. to explain the emergence of modern behaviour in the Late Pleistocene. However, the models in question make rather strong assumptions about the distribution of skills among social learners and about the selectivity of social learning strategies. Here I examine the behaviour of these models under more conservative and, on empirical and theoretical grounds, equally reasonable assumptions. I show that, some qualifications notwithstanding, Henrich's model largely withstands my robustness tests. The model of Powell et al., in contrast, does not-a finding that warrants a fair amount of skepticism towards Powell et al.'s explanation of the Upper Paleolithic transition. More generally, my evaluation of the accounts of Henrich and of Powell et al. helpfully clarify which inferences their popular models do and not support.     

New ideas in ungulate phylogeny and evolution

Most of the ungulates (hoofed mammals) that survive today belong to the orders Artiodactyla (even-toed ungulates) or Perissodactyla (odd-toed ungulates), and are known for their herbivorous specializations (e.g. the ruminant type of stomach), for their large body size (e.g. hippos or rhinos) or for their fleetness of foot (e.g. antelope or horses). Yet these present-day examples represent the specialized end-points of a large Tertiary radiation of hoofed mammals. There was a bewildering variety of small generalized early Tertiary forms, even including some carnivorous taxa. In addition, some specialized island continent ungulate radiations are now either entirely extinct (the South American ungulates), or are represented by only a few living members (the African 'subungulates'). Recent fossil discoveries, and advances in phylogenetic systematics, have reopened a number of issues in ungulate classification, which have affected our views not only on ungulates themselves, but also on patterns of Tertiary biogeography and evolution.