The 3 papers reviewed here have a central underlying theme: optimization under constraint, a principle that is important in a number of fields, including my own, behavioral ecology. All 3 papers go beyond seeking to measure the fitness of responses to considering how differing processes contribute, or do not, to the fitness of a response. The authors are careful in interpreting the data; the results are mixed and not easy to interpret. The potential for cross-fertilization with other fields is clear. (PsycINFO Database Record (c) 2018 APA, all rights reserved)