The numerical results shown in Fig. 6b agree well with this prediction, indicating that after a transient time of duration t ' N the connectivity increases linearly with time. Since the mean-eld approximation used above predicts that after a transient period the connectivities of all vertices should have the same value given by Eq. (25), we expect that the connectivity distribution becomes a Gaussian around its mean value. Indeed, Fig. 6a illustrates that as time increases, the shape of P(k) changes from the initial power law to a Gaussian. The failure of models A and B to lead to a scale-free distribution indicates that both ingredients, namely growth and preferential attachment, are needed to reproduce the stationary power-law distribution observed in real networks.