The structure of society we have become accustomed too , is only about 5,000 years old . This is a very short time considering.
A lot of what we are , or should i say , what we are adapted for , is only something we watch on wildlife documentaries now.
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I saw an interesting documentary which claimed that the increased social complexity resulting from living in larger and larger communities , may have
resulted in our brain size increasing.
They were able to trace a mutation in one of the genes thought
responsible for brain size , back 5000 years +/- ...around the time that "civilisation".... began and social complexity increased e.g trade etc.
100 to 150 people seemed to be some "natural" limit on the numbers of people in tribes ...later hamlets/villages etc .
If i`m not incorrect , i believe that if you were to make a list of everyone you know, it would not exceed this number.
Unless of course you are a 14 year old girl on Face Book .