Infanticide (or infant homicide) is the intentional killing of infants. Parental infanticide researchers have found that mothers are far more likely than fathers to be the perpetrators of neonaticide and slightly more likely to commit infanticide in general. Anthropologist Laila Williamson notes that "Infanticide has been practiced on every continent and by people on every level of cultural complexity, from hunter gatherers to high civilizations, including our own ancestors. Rather than being an exception, then, it has been the rule." In many past societies, certain forms of infanticide were considered permissible.