In 2007, shortly after the release of my first book The Evolutionary Bases of Consumption, I was invited by my good friend Peter M. Todd to speak at the Cognitive Sciences Colloquium at Indiana University. As part of the same trip, I was fortunate enough to also speak at the School of Informatics of Indiana University-Purdue University at Indianapolis (on the kind invitation of Karl MacDorman). You can watch my lecture here. During my visit, I had a chance to meet many lovely colleagues, all of whom were conducting fascinating works. At one point, I visited the lab of Eliot Smith, a social psychologist whose team had collected data on Facebook users. I asked casually whether they had collected information on individuals’ average number of Facebook friends across their sample, to which he answered in the affirmative. I ventured that I would be willing to bet that the number was around 150 (which proved to be correct). I was able to offer this guess because I was familiar with Dunbar’s number, which stipulates that the human brain’s computational capacity to manage social relationships is set around that number (see the recent Businessweek article on Dunbar's number here). In my 2011 trade book The Consuming Instinct: What Juicy Burgers, Ferraris, Pornography, and Gift Giving Reveal About Human Nature, I cite two studies that have confirmed that the average number of Facebook friends is indeed around 150 (see p. 317, footnote 26 for the references).