A study of migration’s origins suggests that, "Evolution tossed up two distinct types of individuals: 'leaders,' who followed environmental cues and ignored everyone else, and 'sociable' individuals, who were attracted to others but themselves oblivious to the cues." Some of the the study’s simulation are troubling. For instance, over time, the simulated populations tended to settle into a ratio with far more followers than leaders. Inuit hunters, incidentally, used to allow lead animals to pass, hunting only from the middle of the pack. There is modern fear that, "Migration may vanish at a scale measured in human years, and recover at time scales measured in planetary cycles."