Men who lack positive role models, says Dr Amelia Kleijn, who interviewed 10 men serving sentences around the country for raping children under the age of three.
Kleijn, a practising social worker with extensive experience with victims and perpetrators of gender-based violence, will present her study - "The demographic profile and psychosocial history of a group of convicted perpetrators of the rape of children under the age of three years" - at the annual Institute for Security Studies Crime Conference today.
"What stands out with the 10 men I interviewed and such offenders broadly, is the lack of positive role models - someone who can show or teach them that there is something better, beyond their current circumstances," she said.
"I'm not talking of a 'Mandela-like role model'. I mean a teacher, brother, uncle, father, religious leader or taxi driver. Any man who can show a boy an alternative way to behave. That is the one element that seems to separate these men - the lack of such a role model."
Kleijn said millions of South African men have grown up in hardship, many have grown up in single-parent households, have experienced abject poverty, but do not turn out to be rapists or abusive people.
She said all the child rapists she interviewed were driven by feelings of revenge and their actions were triggered by an incident that sparked anger.
"One of the men said he raped a baby because he was angry that his kettle was stolen," she said.
She said all the men she interviewed did not have a high school education, or did not finish primary schooling. Others did not go to school at all.
They were beaten severely as children.
They were not employed for the two years preceding the rape though they tried their best.
They were angry at the injustices of the world and one day something happened that made them snap.
Kleijn said she spent a lot of time with the men, one of whom laughed and exclaimed: "I do not know, lady," when asked if he did not fear that he would suffocate a toddler while raping her.
"This clearly illustrates the mark of a psychopath - someone who has no remorse or empathy for others," Kleijn said.
She said one of the men she interviewed raped a two-and-a-half-year-old child after his drinking buddies made a joke about his mother's genitalia.
She said the jokes, the rapist admitted, angered but also aroused him.
"Another, who had three children of his own, raped his three-month-old niece because he was jealous of his sister," Kleijn said.
The man said he could not stand that his sister was able to better provide for her child while he couldn't take care of his children.
Kleijn said often the men were related to the child and angry at people related to the child.
She said her research dispelled the myths that this kind of crime started post-1994 or was related to cleansing rituals to cure HIV.