Animal morphogenesis

Abstract

Morphogenesis and cell differentiation are interdependent during the embryonic development of metazoans1 leading from the fertilised egg to the organism capable of reproduction. Morphogenesis and differentiation also come into play throughout the life of the organism, in the physiological processes of cell renewal or regeneration and in many pathological processes such as cancerogenesis. In fact, the egg is just one stage in the cycle of life itself, caught up in a spiral that has been constantly turning for nearly four billion years. These two time scales, in which intervene ontogeny and phylogeny respectively, are one of the aspects of the complexity of life. Contrary to the theses of Ernst Haeckel,2 ontogeny does not recapitulate phylogeny,3 but the two are interdependent and the one is hardly intelligible without the other. On the one hand, the unique cell of the egg and the processes of morphogenesis are the culmination of a long construction about which we can only speculate. On the other, the emergence of new life forms must pass through the sieve of ontogeny, in the sense that all variations in phenotype have embryological foundations and only those variations that do not compromise the embryonic viability of the organism will be transmitted from generation to generation. Moreover, conceiving the continuity of living beings through the cell prevents us from forgetting that what is transmitted from one generation to the next is not only DNA, but the whole organisation and structuring of the cell and its components, without which the DNA sequence would be nothing. © 2011 Springer-Verlag Berlin Heidelberg.