Helpers and reproductive behavior in birds and mammals

Cooperative breeding - in which some adults forgo independent breeding and remain as subordinates within a group, helping to raise the offspring of others - occurs in between 3% and 10% of vertebrates. The structure of such systems varies greatly, from pairs with helpers-at-the-nest to communal breeders, and may include young helpers or postreproductive 'grandparents. ' That some individuals spend part, or all, of their lives helping others to reproduce contradicts the concept of 'selfish' natural selection and provides an intriguing evolutionary paradox. When and why such apparently altruistic behavior occurs has, therefore, been the focus of much study. While constraints and the benefits of group living may persuade individuals to remain as subordinates, indirect 'kin' benefits or direct benefits (such as becoming a breeding helper) appear to favor the subsequent evolution of helping. Cooperative behavior can have wide-ranging consequences, not only on the biology of the cooperative species, but also on those species it interacts with.