We know that the two experiments have been independent, because the gulf that divides eubacteria from archaebacteria is simply enormous, but we also know that in both cases they ended up by producing bacteria, and this is highly instructive. It tells us that the bacterial cell was not a starting point, but an end result, and it also tells us that there were different ways of achieving that result. The bacterial cell becomes in this way almost a “logical” solution that was discovered many times over, not an isolated accident that was produced by an extraordinary piece of luck at the beginning of life.

The cytoskeleton

A cytoskeleton is absolutely essential for typical eukaryotic processes such as phagocytosis, mitosis, meiotic sexuality, ameboid movement, nuclear assembly and chromosomes’ three-dimensional organization, i.e. for all those features that make eukaryotic cells so radically different from bacteria. It is not surprising therefore that a large consensus exists on the idea that the origin of the cytoskeleton was probably the most important invention for the development of the eukaryotic cell (Cavalier-Smith, 1987). The stages of eukaryotes’ evolution are still shrouded in mystery, but it seems reasonable, as we have seen, to assume that the first cytoskeletons were developed either to favour the movements of phagocytosis or to protect cells from sodium’s osmotic damages.
The evolution of the other stages is more difficult to reconstruct, because the cytoskeleton is in reality an integrated system of three cytoskeletons made of specific molecular fibers (microfilaments, microtubules and intermediate filaments) which give complementary contributions to the three-dimensional form of the cell and to its mobility. Perhaps it would be more accurate to say that the system behaves both as a cytoskeleton and as a cytomusculature (as suggested by Alberts et al.), but even these terms are not entirely appropriate, because do not convey the idea that the cytoskeleton and the cytomuscles are in a continuous state of assembly and disassembly, and can assume very different three-dimensional configurations.