<p>This review examines modern companion dog keeping from both biological and cultural evolutionary perspectives. Dog keeping is explored as a trait that has evolved from being adaptive, contributing to the survival and prosperity of human populations, to possibly being neutral or even maladaptive in modern contexts on the population level. Currently, many people in Western cultures regard dogs as family members or “fur babies”, even though investing money, time, and emotional commitment in them does not directly increase biological fitness. This new kinship can be better understood through a cultural evolution framework, which is compared to the biological (Fisherian) runaway model to understand how human behaviours can evolve beyond their original utility. For future studies, the review proposes exploring whether and how well dogs can be substitutes for human relationships, their impact on human fertility and social networks, who benefits from dog keeping, and for whom keeping a dog is unnecessary or harmful.</p>