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

Abstract

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.

Keywords: anxiety; pediatric bone fracture; playground equipment; risky play.

Figure 1.

Playground falls and forelimb fractures. (a) Angular fractures (arrows) of the radial and ulnar diaphyses of a 6-year-old male. The radial fracture is complete and involves both cortices; however, the ulnar fracture is incomplete with cortical and buckle fractures, exemplifying so-called greenstick fractures. Greenstick fractures are common among children <10 years of age when an angulated longitudinal force is applied along the bone of an outstretched arm. Case courtesy of Samir Benoudina, Radiopaedia.org, rID: 21674. (b) L.D.F. at six years old in 2002, when radio-ulnar fractures from falls were treated with hard casts; photograph by Steve Fannin, reproduced with permission. (c) Today, most radio-ulnar fractures are treated with soft splints; photograph by Jennifer Bernstein, reproduced with permission.

Figure 2.

Rise and fall of Hinton’s jungle gym/monkey bars in New York City. (a) Children climbing in Central Park circa 1942. Photograph by Majory Collins, source: Library of Congress. (b) Closure and subsequent erasure of Hinton’s legacy at the 83rd Street Playground in Riverside Park. Photograph taken in 1996 by Steve Burman. © New York Times, reproduced with permission.

Figure 3.

Suspensory behaviors of juvenile primates. (a) Juvenile chimpanzees spend more time climbing and swinging than adults [86], a pattern shared with humans; photograph by Eric Kilby, reproduced with permission. (b) Child arm-swinging on modern-day monkey bars with a maximum height of 2.2 m. Compare the mulched surface with those from earlier eras in Fig. 2. Location: Norwich, Vermont, USA; photograph by Z.M.T. (c) In Europe, adventure playgrounds are designed to promote thrill-seeking behavior, including potential fall heights exceeding 3 m; photograph by N.J.D. (d) Street sign highlighting the adventurous philosophy of Craigmillar Castle Park Playground, Edinburgh, Scotland; photograph by N.J.D.

Figure 4.

A seven-year-old boy climbing on monkey bars suffered a fall, resulting in a displaced fracture of the right distal radius (arrow). Despite the severity, the attending orthopedic surgeon opted for nonoperative treatment. Serial radiographs over the next 15 months illustrate the natural remodeling of bone. Case history and images courtesy of James Gamble, Stanford University School of Medicine.