Wouldn't it be more prudent to (x-)post this question to /r/AskSocialScience ? Maybe they will be able to shine more light on this question.
150 - the book you want is Grooming, gossip and the evolution of language, by Robin Dunbar. http://www.amazon.com/gp/aw/d/0674363361?cache=08ffb2ca2125067bdd4dc6a42f6ffdb5&pi=SY200_QL40&qid=1405090172&sr=8-1#ref=mp_s_a_1_1
Removed for being a poll-type question.