During observations at the Luo Scientific Reserve in Wamba, Democratic Republic of the Congo, the scientists saw the mother bonobos (Pan paniscus) carrying, grooming, nursing, and sharing food with their adoptees, who were in excellent health and treated well by their new social groups. The team’s analysis of DNA extracted from the infants’ faeces confirmed that the youngsters were genetically unrelated to the groups they lived in.“Bonobo mums open their arms to outsider orphans” at Nature
Why do they do it? Various explanations are offered: The researchers suggest, “In both cases, adoptees had no maternal kin-relationship with their adoptive mothers. Both adoptive mothers already had experience of rearing their own offspring. Instead, these cases of adoption may have been driven by other evolutionary adaptive traits of bonobos, such as their strong attraction to infants and high tolerance towards immatures and out-group individuals.”
Other sources, reasoning according to Darwinian evolution, have suggested that groups have evolved to select only the fittest from outside their kinship group so that they can strengthen their odds of group survival. But then how would the adopting animal know that the abandoned orphan was “the fittest”? Some sources suggest, maybe the animal really doesn’t know the difference.
But wait. Among dogs and cats, adoption, including interspecies adoption, has often been documented.
Cats who have kittens adopt puppies. They do so despite the fact that unusual problems develop because puppies are competitive about nipples but kittens are territorial:
Cats also adopt puppies when they have lost their kittens. The mother’s task is made a bit easier in that case by the fact that all the puppies behave like puppies and none of them behave like kittens:
But again, wait. We also hear of cats who, as a group, adopt a puppy even if they are not nursing kittens:
Tomcats also adopt kittens. And female dogs will adopt kittens too:
So will male dogs:
Here’s another one where a male dog adopts kittens.
Male animals may not have “mothering instincts” but they may well remember life in a litter. So, if they are inclined, they have some idea how to behave toward a mammal infant.
But the guinea pig is at least a mammal. Not all cats stop at mammals. One female cat adopted ducklings, ignoring any natural urge to eat them:
Nonetheless, we learn from authoritative Nature, that
Plenty of mammals will take in an orphaned infant, but few will adopt one from outside their social group. Now, Nahoko Tokuyama at Kyoto University in Japan and her team have documented two wild bonobos that adopted orphaned infant bonobos from outside their group — a first for great apes other than humans.“Bonobo mums open their arms to outsider orphans” at Nature
But once again, wait. In many of the examples we have seen (or linked), animals adopted animals that were not only outside their “social group,” they were outside their species altogether! (guinea pig, ducklings)
So the great apes — other than humans, who adopt both fellow humans and a variety of animals — are outliers among those mammals whose behavior we have studied a good deal. That is, adoption might be common among wolverines and cougars but we might not know about it because they are difficult to study compared to dogs and cats.
Could this be a clue?: Most animal whose adoption behavior we have catalogued were domestic animals cared for by humans. They were not especially (or anyway not immediately) worried about survival. For them, food is found in the cupboard by pleading, not the wilderness by hunting or foraging. Perhaps they can afford to show qualities that they would not otherwise show, as a result of living with humans.
In a way, the willingness of our domestic animals to adopt other animals’ offspring — relative to that of the bonobos, according to researchers — is an argument for human exceptionalism. Given a chance, we break nature’s rules. We do things differently.
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