Most research professors spend their days writing grants, teaching and managing graduate students, so when Stanford’s David Kingsley, PhD, ventured from his office to his lab, pulled out a scale and started weighing 114 pairs of manatee pelvic bones, it was a sign that something was afoot. The results of Kingsley’s efforts make his departure from the routine worthwhile. He found that in almost every case, the left pelvic bone outweighed the right. Although seemingly trivial in difference—the average left pelvic bone is a mere10 percent larger than its right-side partner—that difference carries big weight in evolutionary significance. It suggests...