noun. 1. with regard to animal behavior research, the swapping of children between litters as a way of parting the impacts of hereditary traits from formative encounters. 2. a like method utilized for researching the impact of hereditary variables in the growth and enhancement of n illness. It comprises either (i) having the children of mothers and fathers who do not exhibit the illness being researched raised by substitute parental figures who do, or (ii) having the children of mothers and father who do exhibit the illness be raised by substitute parents who do not.