From the zygote, pluricellular organisms are produced by serial mitosis. Would this formation be possible if every cell made by mitosis had an identical life in relation to its antecedent cells? How did evolution solve that problem?
The formation of complex and distinct pluricellular organisms would not be possible if mitosis in embryos formed only daughter cells with an identical life history as the mother cell, as there would not be differentiation and structural or functional specialization between cells.
Evolution solved the problem forming the cellular differentiation process by which, motivated by stimulus not yet well-known by science, dissimilar and specialized cell lineages gave birth to dissimilar tissues, organs and systems that, as a whole, form the pluricellular organisms.
Cellular differentiation probably is a very intricate process that activates and inactivates some genes within the cell in response to some stimulus.