As the inset of Fig. 4b shows, the numerical results are in good agreement with this prediction. Thus, older (smaller ti) vertices increase their connectivity at the expense of the younger (larger ti) vertices, leading with time to some vertices that are highly connected, a “rich-gets-richer” phenomenon that can be easily detected in real networks. Furthermore, this property can be used to calculate analytically. Using (6), the probability that a vertex has a connectivity ki(t) smaller than k, P(ki(t) ¡ k), can be written as