Natural selection leads to maladaptive behavior through several interrelated means. New adaptations may be constrained by designs resulting from past adaptations, there may be maladaptive by-products of adaptive responses, and environments may change faster than the capacity to respond to them. The behavior of hosts of avian brood parasites provides an example, and it is argued that human pet keeping is another, involving the manipulation of human responses that evolved for other purposes. This leads to strong attachments by humans to their pets, which are underpinned by the following: (a) infant schema, which may be maintained in adult pets; (b) anthropomorphism; (c) motherese or infant-directed speech, which further facilitates the development of the human–pet bond; and (d) the ability to regard attachments to pets more favorably than those to humans. Adaptations by pet species facilitate human attachments, and support the view that pets manipulate the human owners.