Study Shows How Mongooses Create Egalitarian Societies

Mongooses give birth on the same day in the same den so a mother mongoose has no idea who her pups are. That ignorance leads to a fairer society, study shows

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Banded mongooses which took part in the study.
Banded mongooses taking part in the study.Credit: Harry Marshall
Gid'on Lev
Gid'on Lev

It’s one of the most famous experiments in the history of political thought. American philosopher John Rawls asked how a society would look if its principles are all written by a group of rational people. He suggests that we should imagine that we are sitting behind a “veil of ignorance” that keeps us from knowing who we are and identifying with our personal circumstances – gender, sexual proclivities, economic situation, ethnic origin, religious affiliation, the value of our assets, and so on. By being ignorant of our circumstances, we can more objectively consider how societies should operate.

Behind such a “veil of ignorance,” Rawls suggested, the fairest possible social convention would be formulated. If every person is asked to choose among three options – the members of Group A oppress the members of Group B, Group B oppresses Group A or oppression is forbidden – it is likely that he would choose the third option, given the fact that he does not know his origin, gender and religion.

Rawls published this thought experiment exactly 50 years ago, in his book “A Theory of Justice.” Despite the great interest aroused by his theory, man is still a species that excels in its ability to behave unfairly. But it turns out that throughout evolution another mammal has adopted precisely the idea of the veil of ignorance, and even implemented it in a sophisticated manner.

Banded mongooses. Better nourished mothers look after the smaller pups. Credit: Harry Marshall

A study published in the scientific periodical Nature Communications discovered that mongooses have particularly egalitarian societies, thanks to the fact that the parents have no idea about the identity of their pups. Pregnant mongooses all give birth to their offspring at the same time, on the same morning, in a shared underground den. This situation, wrote the researchers, creates a “veil of ignorance” regarding the blood ties between the adult individuals and the litter of pups.

In the study, seven groups of common banded mongooses (Mungos mungo) living in the wild in Uganda were studied. In the experiment half the pregnant females received a cooked egg every day, while the other future mothers received no extra food. The average weight of the pups born to the females from the first group was 165 grams, compared to 142 grams for the pups in the second group. In a period where no extra food was given to any mongoose there were no clear differences in the weight of the pups.

Ignorance is bliss

After the birth it was found that the mothers who were better nourished actually took care of the smaller pups, who were born to the unprivileged mongooses, rather than their own pups. In that way, within a short time the differences in size and weight between the pups in the two groups disappeared. Within 30 days after birth, the pups of the mothers who had received extra food weighed an average of 315 grams, compared to 299 grams in the second group. And 60 to 90 days after birth, the pups of mothers who received additional food weighed an average of 414 grams, compared to 421 grams in the group whose mothers didn’t receive more food.

The authors of the article, Dr. Harry Marshall of the University of Roehampton in London, and Prof. Michael Cant of the University of Exeter, told Haaretz that they could have expected that there would be a selection that would give preference to mothers who identify their offspring and give them preferential treatment, as happens among most species of animals. However, they said, when mothers identify their own infants they often kill those that aren’t theirs. It is known that females have better chances of becoming pregnant and the infants have better chances of surviving, in a situation where there is no infanticide.

Seven groups of common banded mongooses (Mungos mungo) living in the wild in Uganda were studied. Credit: Harry Marshall

Marshall said that “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.”

And Cant added: “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.”

Dr. Amiyaal Ilany, a zoologist from Bar-Ilan University, said: “The research of Marshall and Cant points to the fact that in this society of mongooses there is progress in the direction of a super-organism, as happens among social insects. However, it’s not certain that they’ll continue to develop in that direction. The question here is one of group selection versus kin selection.

“Up until 50 years ago there were many supporters of the idea of group selection. At the time they thought that if there are many individuals who contribute to the success of the group, it will probably be more successful than a group in which the individuals take care only of themselves and their kin.

“But over the years it was discovered that it doesn’t work like that in most cases. Let’s say that there are two kibbutzim in which everyone contributes to the community – but then there’s a mutation and in one of the kibbutzim someone is born who doesn’t contribute. This individual will multiply faster, because he doesn’t work but still benefits from the resources like everyone else. That leads to a situation where the other kibbutz, in which they all help one another, is in danger of invasion. In order for the altruistic kibbutz to win, there has to be a mechanism that destroys kibbutzim in which there are parasitic individuals,” says Ilany.

“Similarly, in nature there is a need for a selection that is strong enough and fast enough so that the parasites will be eliminated before they enter altruistic groups and spread their genes there. In almost all the species that isn’t found, because usually there isn’t a situation in nature in which concern for yourself is eliminated. Herein lies the unique feature of the mongooses according to the new study – a situation is created in which the females give birth together, which encourages helping unidentified individuals from the group. It will be fascinating to examine whether that is a stable situation over the long term.”

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