When faced with a predator or sudden danger, the heart rate goes up, breathing becomes more rapid, and fuel in the form of glucose is pumped throughout the body to prepare an animal to fight or flee.

These physiological changes, which constitute the “fight or flight” response, are thought to be triggered in part by the hormone adrenaline.

But a new study from Columbia researchers suggests that bony vertebrates can’t muster this response to danger without the skeleton. The researchers found in mice and humans that almost immediately after the brain recognizes danger, it instructs the skeleton to flood the bloodstream with the bone-derived hormone osteocalcin, which is needed to turn on the fight or flight response.