Evolving the human niche

This is the author accepted manuscript. The final version is available from the National Academy of Sciences via the DOI in this record

Behavioural homogenisation with spillovers in a normative domain

The importance of culture for human social evolution hinges largely on the extent to which culture supports outcomes that would not otherwise occur. An especially controversial claim is that social learning leads groups to coalesce around group-typical behaviours and associated social norms that spill over to shape choices in asocial settings. To test this, we conducted an experiment with 878 groups of participants in 116 communities in Sudan. Participants watched a short film and evaluated the appropriate way to behave in the situation dramatized in the film. Each session consisted of an asocial condition in which participants provided private evaluations and a social condition in which they provided public evaluations. Public evaluations allowed for social learning. Across sessions, we randomized the order of the two conditions. Public choices dramatically increased the homogeneity of normative evaluations. When the social condition was first, this homogenizing effect spilled over to subsequent asocial conditions. The asocial condition when first was thus alone in producing distinctly heterogeneous groups. Altogether, information about the choices of others led participants to converge rapidly on similar normative evaluations that continued to hold sway in subsequent asocial settings. These spillovers were at least partly owing to the combined effects of conformity and self-consistency. Conformity dominated self-consistency when the two mechanisms were in conflict, but self-consistency otherwise produced choices that persisted through time. Additionally, the tendency to conform was heterogeneous. Females conformed more than males, and conformity increased with the number of other people a decision-maker observed before making her own choice

Individual decision making and the evolutionary roots of institutions

Just as many aspects of individual decisions are sometimes called unconscious or automatic, we know that some institutions have evolved through unconscious, nondeliberative mechanisms. Their function can also be largely nondeliberative, as in the case of some institutions that may structure behavior without requiring any reflection on the part of the participants. On the other hand, political institutions exist for the purpose of bringing deliberative mechanisms to bear on institutions in the hope of changing them for the better. The immense project of building an integrated explanation of institutions from individual brains to nations-has only barely begun. In this chapter, we report on our discussions that attempted to sketch the mechanisms that connect individuals to large-scale institutions. We begin with a discussion of current thought on the design of individual decision making. If institutions regulate behavior, then presumably the mechanisms that have evolved to produce individual behavior will be relevant to the broader enterprise of integrating these two scales of explanation. Then we explore ways in which institutions may have evolved, both as a result of individual decision making and as a result of processes distinct from those that govern individual behavior. We approach this topic from two perspectives. Seen one way, unconscious psychological forces constrain the design of institutions, sometimes powerfully. Seen another way, unconscious population-level processes create functional institutional design that few social architects could conceive of with their individual deliberate faculties

A critical test of the assumption that men prefer conformist women and women prefer nonconformist men.

Five studies tested the common assumption that women prefer nonconformist men as romantic partners, whereas men prefer conformist women. Studies 1 and 2 showed that both men and women preferred nonconformist romantic partners, but women overestimated the extent to which men prefer conformist partners. In Study 3, participants ostensibly in a small-group interaction showed preferences for nonconformist opposite-sex targets, a pattern that was particularly evident when men evaluated women. Dating success was greater the more nonconformist the sample was (Study 4), and perceptions of nonconformity in an ex-partner were associated with greater love and attraction toward that partner (Study 5). On the minority of occasions in which effects were moderated by gender, it was in the reverse direction to the traditional wisdom: Conformity was more associated with dating success among men. The studies contradict the notion that men disproportionately prefer conformist women

Positivity of the English language

Over the last million years, human language has emerged and evolved as a fundamental instrument of social communication and semiotic representation. People use language in part to convey emotional information, leading to the central and contingent questions: (1) What is the emotional spectrum of natural language? and (2) Are natural languages neutrally, positively, or negatively biased? Here, we report that the human-perceived positivity of over 10,000 of the most frequently used English words exhibits a clear positive bias. More deeply, we characterize and quantify distributions of word positivity for four large and distinct corpora, demonstrating that their form is broadly invariant with respect to frequency of word use.Comment: Manuscript: 9 pages, 3 tables, 5 figures; Supplementary Information: 12 pages, 3 tables, 8 figure

The biological origin of linguistic diversity

In contrast with animal communication systems, diversity is characteristic of almost every aspect of human language. Languages variously employ tones, clicks, or manual signs to signal differences in meaning; some languages lack the noun-verb distinction (e.g., Straits Salish), whereas others have a proliferation of fine-grained syntactic categories (e.g., Tzeltal); and some languages do without morphology (e.g., Mandarin), while others pack a whole sentence into a single word (e.g., Cayuga). A challenge for evolutionary biology is to reconcile the diversity of languages with the high degree of biological uniformity of their speakers. Here, we model processes of language change and geographical dispersion and find a consistent pressure for flexible learning, irrespective of the language being spoken. This pressure arises because flexible learners can best cope with the observed high rates of linguistic change associated with divergent cultural evolution following human migration. Thus, rather than genetic adaptations for specific aspects of language, such as recursion, the coevolution of genes and fast-changing linguistic structure provides the biological basis for linguistic diversity. Only biological adaptations for flexible learning combined with cultural evolution can explain how each child has the potential to learn any human language

Conservatism in Laboratory Microsocieties: Unpredictable Payoffs Accentuate Group-Specific Traditions

Theoretical work predicts that individuals should strategically increase their reliance on social learning when individual learning would be costly or risky, or when the payoffs for individually-learned behaviors are uncertain. Using a method known to elicit cumulative cultural evolution in the laboratory, we investigated the degree of within-group similarity, and between-group variation, in design choices made by participants under conditions of varying uncertainty about the likely effectiveness of those designs. Participants were required to build a tower from spaghetti and modeling clay, their goal being to build the tower as high as possible. In one condition, towers were measured immediately on completion, and therefore participants were able to judge the success of their design during building. In the other condition, participants’ towers were measured five minutes after completion, following a deliberate attempt to test the tower’s stability, making it harder for participants to judge whether an innovative solution was liable to result in a good score on the final measurement. Cultural peculiarity (i.e. the extent to which a design could be identified as belonging to a particular chain) was stronger in the delayed measure condition, indicating that participants were placing greater reliance on social learning. Furthermore in this condition there was only very weak evidence of successive improvement in performance over learner generations, whereas in the immediate measure condition there was a clear effect of steadily increasing scores on the goal measurement. Increasing the risk associated with learning for oneself may favor the development of arbitrary traditions