Cover image: A dog asked to perform a simple task, such as extending its paw, for no reward stops performing if it sees another dog receive treats for performing the same task but will offer the behavior longer without reward if the other dog is not present. This primitive version of inequity aversion may be a precursor to the more complex sensitivity to the efforts and payoffs of joint interaction and has previously been shown in primates, but not dogs. See the article by Friederike Range et al. on pages 340–345. Image courtesy of Friederike Range.