Fig. 1. Animal instincts. Animal instincts. Half-horse, half-human, the mythological centaur Chiron (root, chirourgos: surgeon) taught all of the great heroes with skills related to human health (Jason, Peleus, Asklepios, and Achilles). Following in this tradition, most animal studies are performed to gain insights into human physiology, pathophysiology, and response to new therapies. Unfortunately, many other centaurs (like the female centaur shown here) were more biased and profligate. John P. A. Ioannidis Sci Transl Med 2012;4:151ps15 Copyright © 2012, American Association for the Advancement of Science