Human cooperation and evolutionary transitions in individuality

Egalitarian cooperation linked to central oxytocin levels in communal breeding house mice

Relationships between adult females are fundamental to understanding diversity in animal social systems. While cooperative relationships between kin are known to promote fitness benefits, the proximate mechanisms underlying this are not well understood. Here we show that when related female house mice (Mus musculus domesticus) cooperate to rear young communally, those with higher endogenous oxytocin levels have more egalitarian and successful cooperative relationships. Sisters with higher oxytocin concentrations in the paraventricular nucleus (PVN) of the hypothalamus weaned significantly more offspring, had lower reproductive skew and spent more equal proportions of time in the nest. By contrast, PVN oxytocin was unrelated to the number of weaned offspring produced in the absence of cooperation, and did not vary in response to manipulation of nest site availability or social cues of outgroup competition. By linking fitness consequences of cooperation with oxytocin, our findings have broad implications for understanding the evolution of egalitarian social relationships.

Sperm whale clans and human societies

Sperm whale society is structured into clans that are primarily distinguished by vocal dialects, which may be symbolic markers of clan identity. However, clans also differ in non-vocal behaviour. These distinctive behaviours, as well as clan membership itself, are learned socially, largely within matrilines. The clans can contain thousands of whales and span thousands of kilometres. Two or more clans typically use an area, but the whales only socialize with members of their own clan. In many respects the closest parallel may be the ethno-linguistic groups of humans. Patterns and processes of human prehistory that may be instructive in studying sperm whale clans include: the extreme variability of human societies; no clear link between modes of resource acquisition and social structure; that patterns of vocalizations may not map well onto other behavioural distinctions; and that interacting societies may deliberately distinguish their behaviour (schismogenesis). Conversely, while the two species and their societies are very different, the existence of very large-scale social structures in both sperm whales and humans supports some primary drivers of the phenomenon that are common to both species (such as cognition, cooperation, culture and mobility) and contraindicates others (e.g. tool-making and syntactic language).

Human socio-cultural evolution in light of evolutionary transitions: introduction to the theme issue

Human societies are no doubt complex. They are characterized by division of labour, multiple hierarchies, intricate communication networks and transport systems. These phenomena and others have led scholars to propose that human society may be, or may become, a new hierarchical level that may dominate the individual humans within it, similar to the relations between an organism and its cells, or an ant colony and its members. Recent discussions of the possibility of this major evolutionary transition in individuality (ETI) raise interesting and controversial questions that are explored in the present issue from four different complementary perspectives. (i) The general theory of ETIs. (ii) The unique aspects of cultural evolution. (iii) The evolutionary history and pre-history of humans. (iv) Specific routes of a possible human ETI. Each perspective uses different tools provided by different disciplines: biology, anthropology, cultural evolution, systems theory, psychology, economy, linguistics and philosophy of science. Altogether, this issue provides a broad and rich application of the notion of ETI to human past, present and perhaps also future evolution. It presents important case studies, new theoretical results and novel questions for future research. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.