Arm-swinging riddle answered

PARIS: Biomedical researchers yesterday said they could explain why we swing our arms when we walk, a practice that has long piqued scientific curiosity.

Swinging one's arms comes at a cost. We need muscles to do it, and we need to provide energy in the form of food for those muscles. So what's the advantage?

Little or none, some experts have said, contending that arm-swinging, like our appendix, is an evolutionary relic from when we used to go about on all fours.