Gorillas have complex social groups which resemble 'old friendships' and 'tribes' in humans, scientists have found.

It suggests that humans' advanced lifestyle is much more deeply rooted in evolution than previously believed.

Scientists from the University of Cambridge analysed six years of data on social exchanges between hundreds of western lowland gorillas in the Congo.

Gorillas traditionally either live in small family units, consisting of a dominate male and several females with offspring, or solitary male 'bachelors'.

However the data showed more complicated social layers to gorilla culture.

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Gorillas have complex social groups which resemble 'old friendships' and 'tribes' suggesting that humans' advanced lifestyle is much more deeply rooted than previously believed. Pictured: gorillas at the Nouabale-Ndoki National Park in Congo

The University of Cambridge study suggests social groups, only found in a small number of mammal species, are not due to the unique expansion of the human brain - but handed down by the 'last common ancestor' dating back more than 10 million years ago. Pictured: three western gorilla groups mingling peacefully in Congo

Gorillas would regularly interact with, on average, 13 gorillas outside their unit that were members of their extended families.

In human society, these would translate to aunts, uncles, and so on.

Beyond that, gorillas would interact with a further 39 gorillas they shared no blood relations to.

The study's lead author, biological anthropologist Dr Robin Morrison, said the interaction would be comparable to a tribe or small settlement among early human populations.

The gorilla set up is familiar as it centres around an extended family group, plus 'old friendships'.

This suggests its evolutionary origins date back more than 10 million years and are much more deep rooted than previously believed.

It would mean our advanced lifestyle was not due to the unique expansion of the human brain - but handed down by the 'last common ancestor'.

Commonly known as the 'missing link', the mysterious creature is believed to have been a gibbon-like creature which has long gone extinct.

In the study, published in the Proceedings of the Royal Society B, Dr Morrison suggested that the links between gorillas may originate from their upbringing.

As females move from group to group with their offspring many male baby gorillas grow up together despite not being closely related - similar to stepbrothers.

Occasionally, young males who have left their families at the same time but do not want to strike out on their own, they form 'all-male bachelor groups', which could be a bond-forming period.

Dr Morrison added: 'If we think of these associations in a human-centric way, the time spent in each other's company might be analogous to an old friendship.'

The team also unearthed hints of an even higher social tier of 'periodic aggregations', similar to an annual gathering or festival based around 'fruiting events'.

In fact, Dr Morrison and colleagues say sporadic fruiting schedules of the gorillas' preferred foods may be one reason why they - and consequently maybe we - evolved this 'hierarchical social modularity'.

Gorillas in the study would regularly interact with 13 gorillas outside their unit that were members of their extended families. In human society, these would translate to aunts, uncles, and so on. Pictured: the dominant males of two different western gorilla groups feed peacefully together in Congo

She said: 'Western gorillas often move many kilometres a day to feed from a diverse range of plants that rarely and unpredictably produce fruit. This food is easier to find if they collaborate when foraging.

'Gorillas spend a lot of their early life in the family group, helping to train them for foraging. Other long-term social bonds and networks would further aid cooperation and collective memory for tracking down food that's hard to find.'

A small number of mammal species have a similar social structure to humans.

These also rely on 'idiosyncratic' food sources - whether forest elephants hunting irregular fruitings, or the mercurial fish schools sought by dolphins.

All have spatial memory centres in their brain to rival those of humans. Before now, the species on this short list were far removed from humans via evolution.