Proliferation and differentiation of cells occur in the morphofunctional zones, in the electric field excited by 12 pairs of mother and daughter cells, produced by cambial cell division. Thus, in the daughter cells, the Src SH2 domain is essential for both cytoskeleton formation and tyrosinase activation. If the conditions for strengthening the tyrosinase activity are created in an organism, the amount of the Src participating in the cytoskeleton construction process can decrease to a critical level, which will culminate in the development of a malignant tumor. If the action of a stimulating factor is strong enough, the malignant cells will begin to proliferate at the melanocyte stage, and a melanoma will be formed. If the action of the factors is long but not strong, only the more remote descendants of the daughter cells will proliferate, and a cancer will be formed. Therefore, to assure the normal differentiation of the malignantly changed daughter cells, the action of the tyrosinase needs to be blocked. Thus, all the SH2 domains are utilized in cell cytoskeleton construction.