Economic and Social Research Council
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How the 'happy hormones' run out beyond 150 friends

There's a limit on the number of friends we can keep, and new research shows it's down to a biological conscious/subconscious split in our brains which has been developed through evolution.

Professor Robin Dunbar's initial findings, which were presented at the annual meeting of the American Association for the Advancement of Science (AAAS) in Boston, for the first time demonstrate the influence endorphins (the 'happy hormone') have in limiting our amount of friends.

Previous studies by Professor Dunbar and his team at Oxford Experimental Psychology, at the University of Oxford, have shown that there is a cognitive limit of 150 friends a primate can keep, when maintaining a stable social relationship – this is known as Dunbar's Number. So, despite the fact you may have 500+ friends on social media, such as Facebook, only 150 of them could be classed as real 'friends'. This threshold is largely due to a limit in the size of our brain, and the time commitment it can take to make and maintain friendships – something that is in short supply for all of us. 

However, Professor Dunbar's latest research findings show that our endorphins (and the four other main social neuropeptides – oxytocin, vasopressin, dopamine and serotonin) are also playing a huge part in the quantity of our social networks. Like all the monkeys and apes, the strength of our relationships with close friends depends on the way the endorphin system is stimulated by interactions, usually by physical contact such as grooming.

"Once you go beyond your close circle of friends of five to 15 people, it is less and less easy to use physical contact to trigger the endorphin system, not least because we just don't have the time. But humans have found novel ways of doing this, including laughter, singing and feasting, that allow us in effect to 'groom' virtually with many people simultaneously, and this has allowed us to increase the size of our friendship circle up to 150," Professor Dunbar explains.

"Primates have evolved a dual-process bonding mechanism partly dependent on advanced cognitive abilities – the social brain hypothesis, where we are making conscious, calculated decisions, often based on how much we can trust a person – and partly on the way we activate the endorphin system through social grooming," he added.

"Our research shows that humans have extended both of these to allow us to form unusually large and structurally complex social groups. 

"This research shows how the conscious and subconscious parts of our brain work in tandem when it comes to making friends. 

"It further demonstrates the best numbers for group sizes too; whether this be for measuring how many people to employ in a business, perhaps deciding on how many children you may want to have, or for military use when it comes down to deciding squadron numbers on the battlefield.

Looking beyond this it could be used to judge the effectiveness of large-scale society and how we manage to make mega communities such as the EU, and the United States of America, work."

More detail on the research, which has been funded by the European Research Council, will be released with the launch of the papers in publications over the next year or so.

Notes for editors

  1. At AAAS, which ran from 16 February to 20 February, Professor Dunbar presented more of his evidence during two separate discussions on the topic:
    • 'Angels or Wolves to One Another? What Makes Us Prosocial, or Otherwise? – The evolutionary bases of prosociality' - 18 February 2017
    • 'Why you can't have more friends on Facebook than Dunbar's Number' - 18 February 2017
  2. Other social science research on show at AAAS included:
    • 'Is the risk of Alzheimer’s and dementia declining? Evidence from around the world' – Carol Brayne, University of Cambridge on 14 February
    • 'Bilingualism matters' – Antonella Sorace, University of Edinburgh on 13 February
    • 'Open science: global perspectives and prospects' – James Wilsdon, University of Sussex on 15 February
  3. The Economic and Social Research Council (ESRC) is the UK’s largest funder of research on the social and economic questions facing us today. It supports the development and training of the UK’s future social scientists and also funds major studies that provide the infrastructure for research. ESRC-funded research informs policymakers and practitioners and helps make businesses, voluntary bodies and other organisations more effective. The ESRC also works collaboratively with six other UK research councils and Innovate UK to fund cross-disciplinary research and innovation addressing major societal challenges. The ESRC is an independent organisation, established by Royal Charter in 1965, and funded mainly by the Government.
  4. The European Research Council, set up by the European Union in 2007, is the first European funding organisation for excellent frontier research. It offers three core grant schemes: Starting, Consolidator and Advanced. Every year, it selects and funds the very best, creative researchers of any nationality and age, to run projects based in Europe. The ERC also strives to attract top researchers from anywhere in the world to come to Europe. To date, the ERC has funded around 6,500 top researchers at various stages of their careers.


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