A guided tour of early cellular evolution


Early Evolution. From the Appearance of the First Cell to the First Modern Organisms. By Martino Rizzotti. Birkhäuser Verlag, Basel, 2000. ISBN 3 7643 6191 3, 175 pp. Original edition: Prime tappe dell’evoluzione cellulare’ (Decibel Editrice, Padova).

The main theme and strength of this book is an attempt to elucidate important steps in evolution leading from the first life-like aggregates to modern eukaryotic cells. Before and after this period one has the processes of life’s origin and the origin of multicellular eukaryotes. These latter transitions are given a sketchy treatment, which should not be taken too seriously: brevity is not always the sole of wit.

But, emphatically, the analysis of scenarios for the origins of ATPase, of the flagellum, of the outer membrane of the negibacteria (Gram negative bacteria), of the cell nucleus, of the dictyosomes, of the mitochondrial and plastid symbioses, and the eukaryotic cilium is fascinating, up-to-date and well presented. The author often successfully cuts through the mud generated in this unavoidably hypothetical field. For example, he convincingly argues that the acquisition of mitochondria could not have happened without the prior evolution of phagocytosis, hence of the cytoskeleton and the endomembrane system, and – consequently – of a rudimentary nucleus. Cavalier-Smith has forcefully presented these ideas, but the recent excitement about the origin of mitochondria (based on, among other things, the finding that all present-day eukaryotes seem to have had mitochondria) has overshadowed these cogent arguments. It is time again that researchers in the field appreciate that a fancy idea for the origin of one organelle does not solve the problem of the origin of the eukaryotic cell as whole.

Some of the scenarios presented by the author are original and convincing. In particular, the ideas for the origin of ATPase, the bacterial flagellum, the negibacterial other membrane and the eukaryotic cilium are exciting and partially testable by the analysis of molecular sequence data. It is just a very lucky situation that so many genomic sequences become available these days.

Of course, one is unlikely to agree with everything. The idea that the outer membrane of plastids and mitochondria is a remnant of the phagosome is not substantiated satisfactorily. Also, separate endosymbiotic origins for the plastids of green and red algae seem less and less tenable: recent molecular phylogenies of nuclei as well as mitochondria indicate that these algae are sisters; hence a dual origin for their plastids is not likely.

As in any book with such wide and hypothetical scope, there are some strange usage of terms and misrepresentations. The author insists, on the one hand, that we should not use the term ‘undulipodium’, but on the other hand keeps on using ‘Archaeobacteria’ instead of the common ‘archaebacteria’ form. Also, I was somewhat surprised to read that the spirochetal origin of cilia ‘is strongly supported by Margulis and shared by Maynard Smith and Szathmáry’ (p. 142). Well, in 1987 I was indeed an adherent of this idea, but in The Major Transitions we have expressed our reservations, and now I agree with Rizzotti that the idea is very unlikely to be true. There are occasional examples of strange English (‘endocyted’ instead of endocytosed), but these are not too disturbing. The Index leaves a bit to be desired.

In summary, if you want to share the excitement about a crucial phase of evolution, then buy Rizzotti’s book and take a guided tour.