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Reproductive Skew Theory

  1. Barbora Trubenová,
  2. Reinmar Hager

Published Online: 16 JUL 2012

DOI: 10.1002/9780470015902.a0023661



How to Cite

Trubenová, B. and Hager, R. 2012. Reproductive Skew Theory. eLS. .

Author Information

  1. University of Manchester, Manchester, UK

Publication History

  1. Published Online: 16 JUL 2012


An almost universal characteristic of cooperatively breeding animal groups is the unequal sharing of reproduction within the group, referred to as reproductive skew. Reproductive skew theory has been developed to investigate the adaptive causes underlying the variation in reproduction between and within species seen in nature. From its inception in the late 1970s, skew theory has expanded over the years both conceptually and in its application. Three main types of models are distinguished: Transactional models assume that reproductive shares are offered as a reward for cooperative behaviour, tug-of-war; TOW (or compromise) models assume that reproductive shares are determined by competitive abilities of individuals. Both assumptions are reconciled in the third type of models, most recently developed synthetic models.

Reproductive skew theory makes predictions about the range of skew using a set of key parameters such as relatedness and competitive abilities of group members. Skew theory has been applied to a wide variety of topics in evolutionary biology such as parent–offspring conflict, sex ratio conflict or the evolution of cooperation. Key to skew theory is the question under what conditions groups remain stable and it has thus been advanced as a framework to understand the evolution of sociality.

Key Concepts:

  • Social animals living in groups must often resolve a conflict over the allocation of reproduction.

  • Unequal partitioning of reproduction is termed reproductive skew. Reproductive skew is a degree of reproductive bias in favour of one or a few breeders.

  • Skew theory provides a possible explanation for conflict resolution and adaptive causes of sociality.

  • Several indices of skew exist, suitable for different types of studies and questions.

  • There are three main types of models: transactional, tug-of-war (TOW) (also referred to as compromise) and synthetic models, based on different assumptions and yielding different predictions.

  • Transactional models are subdivided into two categories: concession and restraint models. Concession models assume full control of dominants over reproduction in the group, and reproductive share is offered as a reward for cooperation. Restraint models assume subordinates are free to claim reproduction and are only limited by the threat of eviction.

  • TOW models are based on the assumption that both subordinates and dominants have only a limited control over the reproduction and reproductive share is determined by the mutual competitive abilities.

  • Synthetic models combine features of transactional and TOW models. The maximal and minimal reproductive share of the subordinate for a group to remain stable is determined as in transactional models, while, within the range given by the maximal and minimal share, the exact reproductive share is determined by the competitive abilities of both subordinate and dominant in a TOW scenario.


  • reproductive skew;
  • conflict resolution;
  • transactional models;
  • tug-of-war models;
  • compromise models;
  • sociality;
  • cooperative behaviour