![]() Unlike in the case of Daiya, Cherry, who was one of Sango's unaffiliated adults, was engaged in parenting Sakura for as much time as did Sango. Additionally, we explored the causes of alloparenting among chimpanzees, focusing on two primary factors, namely, the individuals that were most likely to become alloparents and the external triggers for alloparenting behavior.įigure 2(b) shows the occurrence rate of parenting behavior of focal adults toward Sakura, the female twin. We investigated whether and how adult group members (besides the mother) cared for the twins. In other words, to ensure their infants' survival, chimpanzee mothers must take care of them. For example, infant chimpanzees still depend on their mothers for transport by riding on their mothers when they travel 8, 11. In general, the third year of life in chimpanzees is the middle of infancy in their life cycle and they still depend on their mothers in diverse ways. ![]() To investigate the hypothesis that alloparents are necessary for twin rearing, we observed the chimpanzee group at Noichi when the twins were two years old. To date, the twins have been successfully reared by their mother. In April 2009, a female chimpanzee named Sango living in the captive group at the Noichi Zoological Park of Kochi Prefecture, Japan, gave birth to dizygotic male-female twins (male: Daiya, female: Sakura Figure 1). In particular, no research has indicated who is more suitable to become a chimpanzee alloparent or the types of care responsibilities assumed by alloparents. ![]() Although reports from the Jane Goodall Institute supported the idea that chimpanzee mothers can rear twins if alloparents are available, quantitative data remain sparse. These episodes suggested that alloparenting by Gaia reduced the parental burden on Gremlin and thus allowed for the successful rearing of the twins. The Jane Goodall Institute 10 has introduced video episodes indicating that the twins were often taken care of by their older sister Gaia. The twins are still alive and surviving well into adulthood 10. The mother, Gremlin, gave birth to female twins (Golden and Glitter) in 1998 9. This idea is supported by the single case of successfully raised chimpanzee twins in the wild at Gombe. ![]() One of the difficulties in rearing infant twins among chimpanzee mothers might have been the absence of alloparents. Even among captives, 64% of individuals born as twins die by the end of the first year of their birth, whereas only 23% of singletons pass away during the first year of life 6. However, in both these cases, the twins were unable to reach adulthood, as one or both the twins died within few years 7, 8. Additionally, Goodall 8 reported a case of twin birth in the Gombe National Park, Tanzania. For example, Matsumoto-Oda 7 reported a case of twin birth among the chimpanzees of the Mahale Mountain National Park, Tanzania. Some cases of twin births have also been reported in the wild. ![]() According to the data from the International Species Information System (ISIS), one of 59 captive births was multiple 6. Diminishing the parental stress of the mothers of twins might require the involvement of alloparents who share the burden of parenting with mothers such as fathers, extended families and community members 5.Ĭhimpanzees ( Pan troglodytes), the closest relatives of humans, normally give birth to one infant at a time however, they also give birth to twins, albeit infrequently. This occasionally results in maltreatment of twins 4. Maternal depression is at least in part caused by the heavier burden of parenting on mothers of twins than on mothers of singletons 2, 3. Thorpe, Golding, MacGillivray and Greenwood 1 showed that mothers of twins at 5 years had significantly higher malaise scores, indicative of depression, than did mothers of singletons at the same age. In humans ( Homo sapiens), having young twins sometimes has a deleterious effect on the emotional well-being of mothers. ![]()
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