Infant abuse and neglect is not a phenomenon unique to the human species.
In monkeys and apes, some mothers occasionally display violent behavior towards their infants and a few others abandon their infants shortly after birth. In macaque monkeys, infant abuse generally occurs in the first two to three months of infant life. Abusive mothers typically drag their infants on the ground or push, hit, or throw them around. Abusive mothers typically alternate short bouts of abuse with long periods of appropriate care-giving behavior. The consequences of abuse may range from infant distress to serious injury and death.
This project had three main goals: 1) to investigate the occurrence of infant abuse and neglect in two large populations of macaques living at the Field Station of the Yerkes National Primate Research Center in Georgia over a period of thirty to thirty-five years; 2) to observe and study the behavior of macaque mothers who physically abuse their infants; and 3) to investigate possible physiological differences between macaque mothers who abuse their infants and nonabusive mothers.
Information for the first study was obtained from the Animal Records of the Yerkes Primate Center. Data were available for about four hundred pigtail macaques and over three thousand rhesus macaques over a period of five to seven generations.
Behavioral observations of abusive mothers in rhesus and pigtail macaques revealed that these individuals do not show any gross behavioral abnormalities in their social interactions with other group members.
Data analyses showed that in these two populations, 5–10 percent of all infants born every year are physically abused by their mothers and 1–3 percent of them are abandoned shortly after birth. Infant abuse, but not neglect, was concentrated in some families and among closely related individuals such as mothers and daughters, or sisters. Thus, abuse appears to be transmitted across generations along the maternal line, and macaque females that are abused as infants are likely to become abusive mothers themselves. Neglectful mothers were young females who abandoned only one of their offspring, typically the first, whereas most abusive mothers repeated abuse with successive offspring. Moreover, abusive mothers were very consistent in their rates and physical patterns of abuse over time and across infants.
Behavioral observations of abusive mothers in rhesus and pigtail macaques revealed that these individuals do not show any gross behavioral abnormalities in their social interactions with other group members. However, they can be differentiated from other mothers for their controlling parenting styles, as they score higher than controls on measures of maternal protectiveness and rejection. For example, they both restrict their infants’ movements and reject their attempts to make contact more frequently than nonabusive mothers. In pigtail macaques, abuse was often preceded by stressful social events such as aggression within the group or infant kidnapping. Since abusive mothers are not more likely to find themselves in such stressful situations than other mothers, this suggests that abusive mothers are individuals that are particularly vulnerable to stress or with problems in emotion regulation.
The third study found that rhesus macaque abusive mothers did not differ from controls in their profiles of estrogen and progesterone during late pregnancy and early lactation. Since these hormones are involved in the regulation of maternal responsiveness, it does not appear that abusive behavior is the result of a deficit in maternal motivation. Some differences between abusive and nonabusive mothers, however, were found in the activity of physiological systems that regulate responses to stress. This is consistent with the hypothesis that abusive mothers have problems with emotion regulation and raises the possibility that these alterations in responsiveness to stress may be the result of an early trauma, i.e. abuse experienced during infancy.
Maestripieri, D. Wallen, K. & Carroll, K. A. Infant abuse runs in families of group-living pigtail macaques. Child Abuse & Neglect, 21: 465-471, 1997.
Maestripieri, D. Parenting styles of abusive mothers in group-living rhesus macaques. Animal Behaviour, 55: 1-11, 1998.
Maestripieri, D. & Carroll. K. A. Risk factors for infant abuse and neglect in rhesus monkeys. Psychological Science, 9: 143-145, 1998.
Maestripieri, D. Megna, N.L. Hormones and behavior in abusive and nonabusive rhesus macaque mothers. 2: Mother-infant interactions. Physiology & Behavior, 71: 43-49, 2000.