Mongooses rear young in a ‘fair society’, research shows
Mongooses are considered remarkable among small mammals due to their ability to carry out audacious attacks on highly venomous snakes and emerge victorious, but new research
reveals the carnivorous species is also unusually egalitarian. A “fair society” has evolved among banded mongooses because mothers within groups of mongooses all give birth on the same night, and as a result, parents don’t know which pups are their own and which were born to other parents. This characteristic creates a “veil of ignorance” over parentage in the communal creche of pups.
In the new study, which was led by the universities of Exeter and Roehampton, half of the pregnant mothers in wild mongoose groups in Uganda were regularly given extra food, leading to increased inequality in the birth weight of pups. But after giving birth, the researchers found that well-fed mothers gave extra care to the smaller pups born to the unfed mothers – rather than their own pups – and the pup size differences quickly disappeared.
Dr Harry Marshall, of the Department of Life Sciences at the University of Roehampton, said: “In most of the natural world, parents favour their own young. However, in banded mongooses, the evolution of remarkable birth synchrony has led to the unusual situation that mothers don’t know which pups are their own, and therefore cannot choose to give them extra care. Our study shows that this ignorance leads to a fairer allocation of resources – in effect, a fairer society.”
The study examined seven groups of banded mongooses. Half of the pregnant females in each group were given 50g of cooked egg each day, while the other half were not given extra food. Inequality at birth (measured by weight) was wider in breeding periods when food was provided than in periods when no extra food was given.
Professor Michael Cant, of the University of Exeter, said: “We predicted that a ‘veil of ignorance’ would cause females to focus their care on the pups most in need – and this is what we found. Those most able to help offer it to the most needy, and in doing so minimise the risk that their own offspring will face a disadvantage. This redistributive form of care ‘levelled up’ initial size disparities, and equalised the chances of pups surviving to adulthood. Our results suggest that the veil of ignorance, a
classic philosophical idea to achieve fairness in human societies, also applies in this non-human society.”
The authors told The Independent the findings were a “big reveal”, and despite the hypothesis the results could easily have shown the animals were not acting fairly. “We didn’t know whose pups were whose until we got the results of the genetic analyses back, long after we had collected all the behavioural data, so it was a big reveal for us,” Dr Marshall and Professor Cant said.
“We were really pleasantly surprised as it supported the idea that ignorance over personal gain promotes fairness in societies, but equally you could have imagined it going the other way, and the pups who had a head start in life continuing to do better, with the gap between them and the poorer-condition pups continuing to widen.”
They said humans could learn from the mongooses’ unique form of social contract, albeit not from treating their young in quite the same manner. Asked if humans should consider mixing up all the newborn babies and redistributing them, as in the mongoose creche, Dr Marshall and Professor Cant instead provided an existing example of how humans can gain benefits through imposing a veil of ignorance within certain frameworks.
They said: “We are definitely not advocating mixing up newborn babies. Mongooses have simply naturally evolved an offspring care system where adults do not whose pup is whose in the communal group litter. This allowed us to test the idea that ignorance over an individual’s personal gain promotes fairness in their decision-making (that is, a more equal distribution of resources).
“This is a longstanding idea, dubbed the ‘veil of ignorance’ in moral philosophy. A nice modern-day example that illustrates it is that it used to be common practice, for this reason, for US presidents to place their assets into blind trusts, so that they could make decisions for the good of the country rather than themselves.”
The research is published in the journal Nature Communications.
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