Original Publications

1.
Boesch, C., Bolé, C., Eckhardt, N., Boesch, H.
Altruism in forest chimpanzees: the case of adoption.

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The chimpanzees Freddy and Oscar from the East Group share food, Freddy carries Oscar around on his back, Freddy grooms Oscar’s fur, Freddy falls asleep holding Oscar on his arm.

Adoption

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Selfless help for orphans

Among chimpanzees, it is not unusual for orphaned infants to be adopted by group members. Although this happens rarely, a powerful alpha male can also become a loving foster father. Foster parents teach the young chimps everything they need to survive in the jungle, so that they can reach adulthood even without a biological mother.

It is not uncommon for orphaned young chimpanzees to be adopted by members of their group. Over a period of 27 years, a team of researchers headed by Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology witnessed 18 such adoptions in Taï National Park in West Africa. It turned out that kinship was not a decisive factor. More than half of the orphaned young chimpanzees were adopted by males which – with the exception of one single case – were not the orphan’s biological father. In some cases, the males cared for their adopted offspring for many years. They carried them around every day for miles, allowed them to sleep in their sleeping nests, cracked open nuts for them and defended them during conflicts. In two cases, females took in non-related, motherless infants and fed them mother’s milk for several years. Without this full round-the-clock care the babies would not have survived, as young chimpanzees are completely dependent on their mother until the age of five. Even the physical development of older chimpanzee children progresses more slowly if they grow up as orphans.

The surrogate parents need to invest a great deal of effort and energy to provide for offspring from other apes. From the viewpoint of evolutionary biology, adoption among relatives is a sensible strategy as they carry the same genes. For a long time, scientists believed that only humans behave so altruistically towards unrelated members of their own species. Such behaviour had never been observed among chimpanzees held in zoos. It was therefore assumed that they are incapable of empathising with others and realising when help is needed. Thanks to the findings contributed by the field research conducted on the chimpanzees in Taï National Park, this assumption has meanwhile been revised.

Adoption is more common among the Taï chimpanzees than it is among chimpanzee tribes in East Africa. One possible explanation might be that they are at greater risk of falling prey to leopards. In the case of the West African chimpanzees, the constant threat posed by these feline predators has resulted in a strong sense of solidarity within the ape community, as evidenced by the fact that the chimpanzees not only defend each other against their enemy, but also care for group members who are sick or in need of help.

Elke Maier

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How chimpanzees orientate themselves in the jungle

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