The Web of Human Sexual Contacts

The Web of Human Sexual ContactsMany “real-world” networks are clearly defined [1] while most “social” networks are tosomeextent subjective [2,3]. Indeed, theaccuracyofempirically-determined socialnetworksis a question of some concern because individuals may have distinct perceptions of whatconstitutes a social link. One unambiguous type of connection is sexual contact. Here weanalyze data on the sexual behavior of a random sample of individuals [4], and find that thecumulative distributions of the number of sexual partners during the twelve months prior tothe survey decays asa power law with similar exponents α≈ 2.4 for females and males. Thescale-free nature of the web of human sexual contacts suggests that strategic interventionsaimed at preventing the spread of sexually-transmitted diseases may be the most efficientapproach.Recentstudiesofreal-worldnetworks[1]haveformalizedmathematicallythe“six-degreesof separation” concept put forth in the classic study of Milgram [5]. This so-called small-world phenomenon [6] refers to the surprising fact that networks have small average pathlengths between nodes while preserving a large degree of “clustering” [3]. Small-world net-works may belong to three classes—single-scale, broad-scale, or scale-free—depending ontheir connectivity distribution P(k), where k is the number of links connecting to a node[7]. Scale-free networks—which are characterized by a power law decay of the cumulative−αdistribution, P(k)∼ k — may ...