Why Are Our Brains So Large?

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.

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One Response to “Why Are Our Brains So Large?”

  1. your blood doesn t lie Says:

    Hi there, everything is going perfectly here and ofcourse every one is
    sharing information, that’s really fine, keep up writing.

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