by Jonas Weisser and Till Nikolaus von Heiseler

Poster (Mind and Brain Conference)

Background Backchannel Theory of Human Evolution

Introduction: The high degree of prosocial behaviour in humans is seen as a puzzle from an evolutionary standpoint. Cultural Group Selection (CGS) as put forth by Boyd and Richerson makes an important contribution towards solving this puzzle. However, its explanatory power is limited as it requires crossing an adaptive valley and only encompasses roughly the last 200,000 years.

Methods: Through a critical discussion of CGS, an explanatory weakness is emphasised that the authors are already aware of. Whilst arguing that the authors’ explanation is insufficient, an alternative is put forth in the form of von Heiseler’s Backchannel Hypothesis (BCH), capitalising on the same principle CGS is built on, namely equilibrium selection – an integration of intra- and inter-group selection making group selection consistent with the inclusive fitness approach of standard evolutionary theory.

Results: Equilibrium selection requires stable and heritable differences between groups. CGS proposes cumulative culture to create this difference. However, this requires crossing an adaptive valley, as prerequisite traits such as social learning, overimitation, and theory of mind are not explained by CGS. In contrast, the BCH proposes reproductive isolation to create stable and heritable differences between groups. It explains how given only the behavioural traits of chimpanzees (as a proxy for our common ancestor) as prerequisite, an evolutionary system can arise that puts selective pressure on prosocial behaviour through social selection in the form of female choice. The Backchannel allows group beneficial (=prosocial) behaviour of an individual to be translated into its reproductive success.

Discussion: It is argued that the BCH is not only consistent with the core principle of CGS, but that it can solve the adaptive valley problem and extend to encompass roughly the last 6 million years of our ancestor’s evolution.