In the face of fear, whether it be caused by a grizzly bear or an audience waiting to hear you speak, your body initiates a reaction to stress. The breath quickens, the pupils dilate, the heart begins to pound. These automatic responses occur as a part of the so-called fight-or-flight response, the body’s evolved mechanism to threats around us. Scientists have known for decades that this reaction is triggered by hormones released by the adrenal glands, two cone-shaped organs that sit atop the kidneys. Now a new hormone has entered the picture—osteocalcin, a protein produced and secreted by bone.
The experiment was the first in a long series of studies that identified osteocalcin as a hormone involved in metabolism, fertility and muscle function. Recent investigations have suggested the protein may even play a role in brain development and cognition. As these discoveries accumulated, [geneticist Gerard] Karsenty and his colleagues began to wonder why the skeleton, which protects our internal organs and gives us the ability to move, also acts as an endocrine organ with multifaceted roles. This insight led the researchers to the unorthodox hypothesis that perhaps bones evolved, at least in part, to help animals escape from danger.
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