For the last two years, research Yerkes associate Dario Maestripieri and his colleagues have been studying infant abuse and neglect in monkeys. Their findings, which are about to be published in three different journals, indicate that primates may be very good models to study the causes and consequences of child abuse in humans.
In both monkeys and humans, infant abuse and neglect occur with a similar frequency and are transmitted within families across generations, said Maestripieri, an adjunct assistant professor in the Department of Psychology. There also are similarities between the behaviors of abusive monkeys and human parents.
"Most monkey mothers take very good care of their infants," he explained, but some occasionally show violent behaviors "that really don't belong to the normal maternal repertoire." These monkeys don't show these patterns of abuse all the time, however. Most of the time, they are "perfectly normal, socially competent animals, who were raised by their own mothers and live in big social groups with their families," he noted.
Maestripieri has studied Yerkes data on the occurrence of abuse in three species of monkeys-pigtail macaques, mangabeys, and rhesus macaques. Since the center has kept extensive records on all of these animals since the late '50s and early '60s, Maestripieri was able to analyze this information for different generations of monkeys in large families constructed along maternal lines.
He found that abuse seems to be more common in some families than in others. "For example, in the rhesus population I had 57 families, and I found that abuse was only recorded in eight," he said. "And within these families in which abuse occurred, I found that it was particularly frequent between females that were very closely related-like mothers and daughters or sisters." For instance, he explained, five sisters in one family of pigtail macaques abused their infants, but no other monkeys in that family were abusive.
"It's not clear whether there is any biological influence, or these females learn the abuse from their mothers by observing or by experiencing abuse themselves," he said. "But this is interesting, because one of the most peculiar characteristics of abuse in humans is that it's transmitted across generations in families. So it's similar to child abuse to humans."
He also found that the general incidence of abuse in the monkeys was comparable to that of child abuse. "Between 5 and 10 percent of all infant monkeys born in the populations were at risk of abuse or neglect," he said.
Another study-done only with rhesus macaques-involved the direct observation of monkey mothers who abused their infants and compared their behavior to that of good mothers. "I found that abusive mothers are very controlling parents, Maestripieri said, noting, that they restrict their infants behavior and temporarily reject their infants more frequently than nonabusive mothers.
There also were some differences in the social behavior of these abusive mothers with other monkeys in the same group. Abusive mothers were slightly more aggressive toward other adult monkeys than normal mothers, and spent less time in contact or near other monkeys. "In particular, they were approached by other monkeys less frequently," Maestripieri said, "so to some extent, you could say that they were socially isolated more than normal mothers."
Although Maestripieri observed interesting similarities between the abusive behaviors in monkey and human mothers, he acknowledged that these might not be the same thing. Nevertheless, the parenting behavior of primates is more similar to human parenting than that of any other animals," he explained.
Animal models are used for research on many other big societal problems, such as violence, aggression or drug addiction. But basically, Maestripieri said, "nobody's doing any other research on child abuse using animals."