Acquiring Genomes: A Theory of the Origins of Species [Hardcover]

Her new book, Acquiring Genomes: A Theory of the Origins of Species, extends and deepens that argument. Margulis sets out to prove that new species rarely if ever appear as the result of mutation, isolation, genetic drift, or population bottlenecks--the meat and potatoes of neo-Darwinism. Instead she maintains that the major engine of evolutionary change, the source of most of the new forms that natural selection edits, is symbiogenesis--the acquisition of whole genomes as the result of symbiotic associations between different kinds of organisms. (Knowing that some people will seize on her thesis as an attack on the theory of evolution as a whole, Margulis makes it clear that she fully supports Darwin's great discovery of the mechanism of natural selection. She simply thinks that neo-Darwinists have failed to recognize the enormous creative power of genomic mergers.)

Readers who are familiar with Margulis' earlier works will recognize her vivid, personal and sometimes impressionistic writing style. I found this book, co-authored by her son, Dorion Sagan, to be clear and accessible. Starting with Chapter 9, where Margulis presents her latest ideas on the symbiotic origin of the nucleus itself, things get a bit more technical. Margulis makes every effort to help readers through the thicket of important, but at times tongue-twisting terms, and supplements explanations in the text with an excellent glossary. Margulis also presents the findings of several other researchers whose work supports or relates closely to her own.

Readers may or may not close the book convinced that Margulis is right and the neo-Darwinists are wrong. But they will come away with a vastly deeper understanding of the pervasive nature and power of the microbial world, and of symbiosis. Margulis reveals a hidden side of nature, in which microbes have generated most if not all of life's metabolic machinery, in which vastly different life-forms consort in a myriad of ways, and in which the acquisition of entire genomes provides the raw material for great evolutionary leaps. Anyone with a deep interest in biology will gain important insights from "Acquiring Genomes."

Robert Adler, author of Science Firsts: From the Creation of Science to the Science of Creation (Wiley & Sons, 2002).

The main point of this book, which I cowrote, is that, although mutation leads to evolutionary change, all the best examples of speciation, including all that have actually been observed, have been through symbiosis. The greatest amount of biodiversity, including all basic metabolic modes from photosynthesis to oxygen respiration, evolved in the bacteria via mutation and gene transfer. But although given Linnean species names for the sake of convenience and via convention, speciation does not really apply to bacteria, which trade genes (via techniques borrowed by human beings practicing biotechnology) with little regard for species barriers. True speciation only evolved in the eukaryotes--protists, fungi, plants, and animals. These largely sexed beings pose the Darwinian problem of speciation proper. And here all the best examples of speciation involve symbiosis, the coming together of different kinds of organisms. Since Acquiring Genomes was written, more evidence has come to the fore to show that its central thesis--that the presence or absence of genomes, particularly those of microbes, can lead to speciation--is correct. In a recent Montreal conference on molecular biology and phylogeny, for example, John Werren from the University of Rochester in New York showed a picture of a chromosome of a sperm cell from a parasitic wasp: rod-shaped bacteria, Wolbachia, were nestled in the chromosome. Wasps can have their sex change due to the presence of bacteria, and antibiotics can make separate species of jewel wasps interbreed again. At this same meeting Professor Harold Morowitz (who is developing a Universal Metabolic Chart, on the model of the Periodic Table of the Elements) was impressed by the plasticity of ever-changing gene formations--emphasizing the need to look for metabolic pathways shared by most or all organisms to understand life's origins. Because life is an open thermodynamic system, as well as an open informational one, genomic transfer is rampant.

It is important to realize two things that Acquiring Genomes does not say. The book does not say that all bacterial diversity is the result of genome acquisition. As suggested above, and by Canadian biologist Sorin Sonea and others, despite the bacteriological convenience of their species names, bacteria arguably do not have species due both to rampant genetic transfer as well as the premier, zoological definition of species as an interbreeding population; since all bacteria can theoretically trade genes with each other either directly or through through vectors (and do not need to reproduce to do so), the animal definition of species does not really apply to them. The original genetic and metabolic diversity in bacteria must owe significantly to neodarwinian-style mutations but, since bacteria arguably do not possess species, such mutations do not occur for speciation.

As Ernst Mayr suggests in his Foreword, the evidence for speciation by genome acquisition in birds and mammals is not compelling. The argument for genome acquisition here depends on the possible symbiotic status of the ends of chromosomes, called kinetochores. (Bacteria don't have true chromosomes, they have chromonemes.) Because chromosome arrangements differ slightly in closely related mammal species (e.g., dogs and wolves) that no longer breed with each other, and because the spontaneous splitting of these chromosomes may owe to their separate bacterial origin, we make the argument that even vertebrate speciation may owe to the symbiotic aftershocks of microbial genome acquisition. The main point to remember is for every example of speciation for which there is actual evidence, genome acquisition is the causative factor; and that, despite mountains of theory, this is not the case for mutations.

Finally, the thermodynamics section is only an at best tantalizing foretaste of a much more comprehensive argument and regrettably contains a couple of mistakes, such as the characterization of Benard cells as octagonal (they're hexagonal) and appearing from a chemical gradient (they don't; they appear in a temperature gradient). And one final comment: both Lynn and I read Stephen King's On Writing after A.G.'s composition and realized belatedly how much it could have been improved, despite the complexity of some of the arguments, by eliminating further needless words.

This is one of those groundbreaking books that trys to answer one of Charles Darwin's long standing mysteries... how do species originate. Darwin could never quit put his finger on the answer, he was close and I'm sure with time and the right equipment, like what is available today, he might have even solved this nagging question.

Margulis has been working on this same question for the last thirty years and she makes a very convincing argument, symbiotic merger is the main thrust of her thesis in this book. This book has some real mind-spinning ideas and you'll have to know some biochemistry, biology, chemistry, cell-biology to prepare yourself for a provocative wild ride through this book as some of the material directly challenges the assumptions that we hold about diversity in the living world.

Margulis has for many years been the leader in the interpretation of evolutionary entities as the products of symbiogenesis. Symbiogenesis is the major theme of this book. The authors show convinvingly that an unexpectedly large proportion of the evolutionary lineages had their origins in symbiogenesis. Ok, I know some of you are saying what is symbiogenesis, well it's the combination of two totally different genomes form a symbiotic consortium which becomes the target of selection as a single entity. This is achieved by the mutual stability of the relationship, symbiosis differs from other cases of interaction such as carnivory, herbivory, and parasitism.

Now, that I've said all of that, you realize that this book can get pretty deep at times, but the author has a pleasent styled narrative, always keeping the reader involved. Prehaps the greatest merit of this book is that it introduces the reader to the fascinating world of microbes, delving into providing an enthralling description of protists and bacteria.

I found this book to be most enlightening about the enigma of evolutionary biology and how species are formed, comprehensive in scope and supported by scientific theory. This book will make you think. If you want to know about the cutting edge of evolutionary thinking then this is the book for you. To realize that everything on earth is inter-related and that life will carry on when faced with tragedy.