Dunbar’s Number goes to Church: The Social Brain Hypothesis as a third strand in the study of church growth

Abstract

The study of church growth has historically been divided into two strands of research: the Church Growth Movement and the Social Science approach. This article argues that Dunbar’s Social Brain Hypothesis represents a legitimate and fruitful third strand in the study of church growth, sharing features of both previous strands but identical with neither. We argue that five predictions derived from the Social Brain Hypothesis are accurately borne out in the empirical and practical church growth literature: that larger congregations lead to lower active engagement from members; that single-leader congregations are limited to around 150 members; that congregations of 150 are further stratified into smaller functioning groups; that congregations expanding beyond 150 members undergo internal tensions and are forced to reorganise; and that congregations larger than 150 will require structural sub-divisions to retain active member involvement. While these assertions are reflected in the church growth literature and articulate the common sense assumptions of church growth experts, the Social Brain Hypothesis offers a coherent theoretical framework which unifies these observations and thereby represents a distinctive contribution to church growth studies.

The Importance of Hypotheses in Church-Based Research

“…As the study of the growth of churches develops, the theory explaining the phenomena that have been observed grows as well. For example, Bretherton and Dunbar (2020) of the University of Lincoln (UK) have applied Dunbar's (1993) social brain hypothesis to the growth and functioning of churches. The social brain hypothesis states that human brains are limited to forming cohesive groups with a maximum size of approximately 150 members.…”

“…This provides a theoretical framework for understanding congregational growth and structure based on human brain capacity. It leads to several very specific hypotheses (Bretherton & Dunbar, 2020) describing phenomena that have been noted in church growth literature.…”

“…Although these three hypotheses (Bretherton & Dunbar, 2020) describe well-documented phenomena, having a theoretical framework such as the social brain hypothesis (Dunbar, 1993) to understand why they occur provides a structure for developing more effective strategies to address the problems associated with the phenomena.…”

How Church Leadership May Influence Growth by Applying an Organizational Life Cycle Perspective on Church Development

“…In a more recent study, the social brain hypothesis is applied (Dunbar, 1993). Bretherton and Dunbar (2020) used this hypothesis to argue that single-leader churches face challenges of dropping engagement when the number of members exceeds 150. Tensions are created in a restructuring process and may stop or slow down the growth.…”