Commemorating the monkey bars, catalyst of debate at the intersection of human evolutionary biology and public health.

Play is an essential part of childhood, and growing attention has focused on the potential health benefits of 'risky' or 'thrill-seeking' play. Such play behavior is readily observed on any playground, where it can sometimes lead to injuries--most often from fall impacts--that require medical attention. Monkey bars account for ~7% of childhood arm fractures in the USA, an alarming statistic that raises difficult questions over its costs and benefits. Many authors view monkey bars as a public health hazard, but it is plausible that our childhood impulse toward thrill-seeking play is a result of selective pressures throughout our primate evolutionary history. Indeed, emerging evidence suggests that the developmental benefits of thrill-seeking play extend into adulthood, outweighing the occasional costs of injury. Disparate and consequential, these dueling perspectives have fueled debate among health professionals and policymakers, but with little attention to the work of biological anthropologists. Here we call attention to the hominin fossil record and play behaviors of non-human primates, providing a novel perspective that bolsters arguments for the adaptive significance of thrill-seeking play. The moment for such a review is timely, for it commemorates the centennial anniversaries of two playground icons: the jungle gym and monkey bars.