another important moment in primatology occurred when william mcgrew and caroline tutin visited mahale in 1975. extensively familiar with the chimpanzees in gombe national park, they had no reason to expect striking behavioural differences in the same subspecies with the same ecology. nevertheless, the mahale chimpanzees frequently engaged in handclasp grooming, whereas this behaviour is entirely unknown from gombe. one chimpanzee takes the hand of another, which they then lift above their heads, while both groom each other's armpits with their free hands. based on their visit, mcgrew and tutin were the first to seriously question the assumption of "typical" chimpanzee behaviour, an important step towards culture studies on the great apes.