dN dℓ = rN [1 − N N$_{f}$ ] , (4) N ( ℓ ) = N$_{f}$ exp( rℓ ) N$_{f}$ + (exp( rℓ ) − 1) (5) with solution, (see the fitting in Fig. 4c) where N$_{f}$ is the final number of cell types and r = 0 . 65 is the growth rate of cell types. Analysis of the network connectivity reveals that the average number of links per node in the final stages of the entire NHCD is 〈 k 〉 = 2 . 24 (Fig. 4d). Even though 〈 k 〉 ≈ 2, there is a broad degree distribution (scale-free [12], P ( k ) ∼ k $^{$_{−}$γ}$, γ ≃ 3 . 0, SI-Fig. 7). This implies that there is always a small number of crucial cell types that differentiate much more than the 7 as a growth process. The knowledge of the time of appearance of each cell type, T$_{a}$ , makes it possible to follow the cumulative growth of the embryo and fetus in terms of the total number of cell types at time t , N ( t ) as well as the number of cell types that eventually survive in the organism (Fig. 4a). As expected, surviving cells emerge in the later stages of the gestation period. However, the difference between the total and the surviving number of cell types indicates that generation of new types of non-surviving cells takes place even during the final gestation months. The increase of the network size, N ( t ), is initially approximately exponential and after t$_{∗}$ = 40 days changes into a slower growth (Fig. 4a). Only a small percentage of the nodes grow within a given time interval, so that the network activity is focused in a small number of them at a given time. The number of nodes that differentiate at a given time are shown in Fig. 4b. We observe an activity that increases monotonically up to around t$_{∗}$ = 40 days and then drops to lower values. The cross-over time t$_{∗}$ = 40 days observed in Figs. 4a and 4b separates two regimes of growth and approximately corresponds to the time below which most of the cells have a plastic characteristic (i.e., the capability to differentiate) and above which they start to become functional [1]. Interestingly, the two regimes observed in N ( t ) merge into a single universal functional curve when we replot N ( ℓ$_{N}$ 1 ) as a function of the chemical distance to the fertilized egg, ℓ$_{N}$ 1 (Fig. 4c). This result suggests that the topological distance in the network ℓ$_{N}$ 1 is the natural variable to characterize the growth process in a universal form rather than the time. The dynamic of N ( ℓ ) follows a typical logistic (Verhulst) process of population growth where the rate of growth is restricted by environmental limitations: