Posts Tagged ‘dunbars number’

Why Are Our Brains So Large?

September 16, 2012

A recent article1 provides a possible answer. The article’s title is Social Network Size Linked to Brain Size. Perhaps the most prominent hypothesis is that our enlarged brains allow us to be smarter than our competitors. We are better at abstract thinking, better with tools (I am a personal exception here), and better at adapting our behavior than our prey and predators.

In 1992 anthropologist Robin Dunbar (Remember Dunbar’s Number? See healthymemory blog posts, “Why Is Facebook So Popular?”, and “How Many Friends are Too Many?”) published research showing that in primates the ratio of the size of the neo-cortex to that of the rest of the brain consistently increases with increases in the size of the social group. So the Tamarin monkey has a brain size ratio of around 2.3 and an average social group size of around 5 members, whereas a Macaque monkey has a brain size ratio of about 3.8 but a large average group size of around 40 members. Consequently, Dunbar advanced his “social brain hypothesis,” which states that the relative size of the neo-cortex rose as social groups became larger in order to maintain the complex set of relationships necessary for stable co-existence. Moreover, he suggested that given the human brain ratio we have an expected social group size of about 150, the size of what Dunbar called a clan.

Dunbar’s previous worked was focused on differences among species. His more recent work focuses on differences within species. He has found that the size of each individual’s social network is linearly related to the neural volume in the orbital prefrontal cortex. His research has shown that more than just more neural material in the prefrontal cortex is needed. Psychological skills are also needed, especially an ability to understand the other person’s state of mind. This cognitive skill is called a “theory of mind.”

So we have two explanations of why are brain’s are so large. One is that we are better at abstract thinking and adapting our behavior. The other is that the larger brain is needed to accommodate larger social networks that are beneficial to our survival. The astute healthymemory blog reader will likely quickly realize that these two hypotheses are not mutually exclusive. Most likely they are both at work.

1http://www.scientificamerican.com/article.cfm?id=social-network-size-linked-brain-size

© Douglas Griffith and healthymemory.wordpress.com, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

The Adverse Effects of Social Isolation

October 23, 2011

Lonely people have a higher risk of everything from heart attacks to dementia, and from depression to death. However, people who are satisfied with their social lives sleep better, age more slowly and have more favorable responses to vaccines. John Cacioppo of the University of Chicago, an expert on the effects of social isolation, says that curing loneliness is as good for your health as giving up smoking. Charles Raison of Emory University studies mind-body interactions agrees with Cacioppo. He has said, “It’s probably the most powerful behavioral finding in the world. People who have rich social lives and warm open relationships don’t get sick and they live longer.”1

Although it is true that some people who are lonely might not take good care of themselves, Cacioppo states that there are direct physiological mechanisms that are related to the effects of stress. Cacioppo has found that genes involved in cortisol signaling and the inflammatory response are up-regulated in lonely people and that immune cells important in fighting bacteria were more active too. His conjecture is that our bodies might have evolved so that in situations of perceived social isolation, they trigger branches of the immune system involved in would healing and bacterial infection. On the other hand, people in a group might favor the immune response for fighting viruses, which are more likely to be spread among people living in close contact.

It is important to note that these differences relate most strongly to how lonely people believe themselves to be, rather than to the actual size of their social network. Cacioppo thinks that our attitude to others is key here. Lonely people become overly sensitive to social threats and see other people as potentially dangerous. In a review of previous studies that he published last year, he found that disabusing lonely people of this attitude reduced loneliness more effective than giving people more opportunities for interaction, or teaching social skills.2

Only one or two close friends might suffice if you are satisfied with your social life. Problems arise when you feel lonely.3 In the jargon of the Healthymemory Blog, this is largely a matter of transactive memory. Transactive memory refers to shared memories and of the knowledge one has of other memories. These memories can form as a result of person-to-person interactions or via means of technology, such as the internet. It should be noted that having hundreds of friends on Facebook would not necessarily indicate that you are not lonely. “What is important is the quality rather than the quantity of these relationships. An evolutionary biologist, Robin Dunbar, came up with a number he modestly named, “Dunbar’s number.” He bases this number on the size of the human brain and its complexity. He calculates that the maximum number of relationships our brain can keep track of at one time to be about 150 . This number includes all degrees of relationships. This is the maximum number of relationships. The number of close, meaningful relationships is much smaller. He estimates that we have a core group of about five people with whom we speak frequently. I find this absolute number a tad small, but to be in the general ballpark. At the other extreme there are about 100 people with whom we speak about once a year. The 150 number is an absolutely maximum of people we can even generously consider as friends. So Facebook users who have friended several hundred friends have essentially rendered the term “friend” meaningless.” (From the Healthymemory Blog post, “Why is Facebook So Popular?”, also see the Healthymemory Blog post “How Many Friends are Too Many?”).

1From “Trust People” in Heal Thyself by Marchant, J. (2011), New Scientist., 27 August, p. 35.

2Cacipoppo, J. (2010). Annals of Behaviorl Medicine, 40, p. 218.

3This part of this post was based heavily on the article by Marchant in the first footnote above.

© Douglas Griffith and healthymemory.wordpress.com, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

How Many Friends Are Too Many?

November 7, 2010

There are people who boast of having more than a thousand friends on Facebook. A blogger once indicated that he was following over a thousand blogs. Does this make sense? An evolutionary biologist, Robin Dunbar, has come up with an hypothesis that provides an answer.1

The hypothesis is called the social intelligence hypothesis. Dunbar notes that social relationships make demands on cognition that are reflected in larger brains. Apes and monkeys are social animals that have a particularly large neocortex, a region of the brain that regulates language abilities, emotion, and the awareness of others. Our social relationships are much more complex and that is reflected in an even larger neocortex. Our brains consume about twenty percent of our energy. Dunbar has come up with a number called, oddly enough, “Dunbar’s number.” He bases this number on the size of the human brain and its complexity. He calculates that the maximum number of relationships our brain can keep track of at one tine to be about 150 . This number includes all degrees of relationships. He estimates that we have a core group of about five people that we speak with frequently. Personally, I find this number to be a tad low. At the other extreme we have about 100 acquaintaces we speak with about once a year. Although we can quibble about these numbers, I would hang my hat on 150 being the maximum number of people we can call friends.

If you count the number of friends you have had over a lifetime, you might well exceed 150. But it is likely that most of these friends have dropped out and you no longer interact with them regularly. Of course, you are glad to see them again and are happy to chat up old times. However, human relationships take time and cognitive resources, so the number of true friends with whom you interact is limited. Although you might have more acquaintances, know more people, they are probably not adequately characterized as friends.

I would argue that there is a trade-off between the number of friends you have and the quality of these friendships. The number of true friends you have might be much lower than the 150 maximum, but they are likely of high quality. Again, the limitation is one of cognitive resources.

I would also argue that online friends can well be true friends. But they make the same demands on resources and you should spend your cognitive resources wisely.

1Dunbar, R., (2010). How Many Friends Does One Person Need? Dunbar’s Number and Other Evolutionary Quirks. Harvard University Press.

© Douglas Griffith and healthymemory.wordpress.com, 2010. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.