Differences in the way girls and boys climb and in what they remember about nighttime fears suggest that certain human behaviors may be influenced by ancient experiences, says Richard Coss, a UC Davis psychology professor. The differences could be related to how male and female human ancestors sought refuge in trees and on the ground, Coss says. This is one of several cases Coss has been investigating as illustrations of the evolutionary persistence of behaviors. In this example, Coss found in a study of elementary school children that girls significantly outnumbered boys on playground structures, and that in looking at climbing competency, boys were more likely than girls to be injured on climbing equipment. In examining nighttime fears, Coss found that males were more likely to be fearful of something that was at a side location, while females were more likely to report fearing something on the floor or below the bed. These sex differences, he suggests, might reflect 2-million-year-old genetically influenced behaviors that anticipate the locations of nighttime attacks by predators. Coss will present his findings on Monday, July 26, 8:50 a.m., in Wellman Hall, Room 26.