PLoS ONE doi:10.1371/journal.pone.0008901
Altruism in Forest Chimpanzees: The Case of Adoption
Christophe Boesch et al.
Abstract
In recent years, extended altruism towards unrelated group members has been proposed to be a unique characteristic of human societies. Support for this proposal seemingly came from experimental studies on captive chimpanzees that showed that individuals were limited in the ways they shared or cooperated with others. This dichotomy between humans and chimpanzees was proposed to indicate an important difference between the two species, and one study concluded that “chimpanzees are indifferent to the welfare of unrelated group members”. In strong contrast with these captive studies, consistent observations of potentially altruistic behaviors in different populations of wild chimpanzees have been reported in such different domains as food sharing, regular use of coalitions, cooperative hunting and border patrolling. This begs the question of what socio-ecological factors favor the evolution of altruism. Here we report 18 cases of adoption, a highly costly behavior, of orphaned youngsters by group members in Taï forest chimpanzees. Half of the adoptions were done by males and remarkably only one of these proved to be the father. Such adoptions by adults can last for years and thus imply extensive care towards the orphans. These observations reveal that, under the appropriate socio-ecologic conditions, chimpanzees do care for the welfare of other unrelated group members and that altruism is more extensive in wild populations than was suggested by captive studies.
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5 comments:
The paper comments that adoption is "costly."
It is true that chimpanzees would end up sharing resources with a young chimp that is not their child. Yes, that is costly.
But surely chimps are smart enough to perceive that their "relatedness" extends beyond their immediate children.
The paper mentions that male chimpanzees adopted young chimps, both male and female. Since male chimps never completely know who their offspring are, they would probably be more willing than females to look out for the wellfare of the tribe, not just their immediate family. They would most likely not know who their immediate offspring are, in any case.
In adopting a member of their extended family, the chimps would also be able to pass on their "culture", as in food gathering techniques, etc. Passing on culture would likely increase the survivability of the group.
The authors are very cautious not to overstate their claims, but it is touching to read about this chimp group.
Marnie:
I agree with you about male chimps never knowing who their children are and so it may be to their advantage to take the risk of supporting non-offspring. Also these adoptees may be nephews and nieces of the males and so still share a considerable amount of DNA even if they are not offspring.
I'm wondering if anyone has done a study on dolphin adoption. I'd guess elephants too, but the poor male elephants get kicked out of the herd at some point, so in their case, we'd only see adoption by female elephants.
The study is also notable for chimp gender stereotype breakdowns. We think of chimps as pretty sexually dimorphic But, the behavior in the study by the adopting male chimps is very nuturing.
has there been any research to the opposite effect? that like in humans offspring later on supports the parent? i would think that is one explanation, it also explains why adoption would occur way less in captivity where food supply is a completely different phenomenon.
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