Prokaryotes: Trends towards Complexity

Abstract

As the complexity of structures is correlated with the number of proteins which take part in their composition (Section 4.3, beginning), the complexity of organisms is correlated, more or less implicitly, with the number of different cellular types they contain⁵⁷. These types appear during the lifecycle of the species as temporary modification of the single cell in unicellular organisms or, in addition, some of these types may be co-present in multicellular organisms as differentiated cells. The latter organisms usually have unicellular stages, too, and the cells of these stages are usually different from those of multicellular stages. For example, the unicellular stages of Mammals or Birds, i.e., egg, sperm and zygote (or fertilized egg), are obviously very different from any cellular type of the multicellular stages, the only ones which are considered as individuals according to common sense (Section 12.2, beginning).