Never one to shrink from controversy, biologist Margulis (Geosciences/Univ. of Massachusetts, Amherst) and son Dorion (Biospheres, 1990) proclaim with predictable bombast that “symbiogenesis,” the inheritance of acquired genomes, is the prime mover of evolution, by far outranking the role of adaptive mutations in creating new species.
Given that science now accepts Margulis’s earlier observations that chloroplasts and mitochondria, the energy-generating organelles in plant and animal cells, were originally independent bacteria but are now inherited in the cells of higher species, attention should be paid. Indeed, no less an evolutionary authority than Ernst Mayr provides a foreword commending the insights and observations that inform the text, albeit with reservations. The strength of Margulis’s argument rests on studies of bacteria (single-celled organisms without nuclei) and protoctists, “unruly organisms” that have membrane-bound nuclei and include giant kelp, slime molds, amoebae, and Paramecium. For starters, bacteria have no species, she says; they change rapidly, freely exchange genes, and demonstrate a metabolic diversity that shames the mere photosynthesizing or oxygen-based metabolisms of plants and animals. Bacteria were the only life forms on the planet until two billion years ago, when they formed integrated teams to make the first nucleated cells—an event, the authors say, that began the speciation process. From here on, readers are treated to technical examples of genomic teamwork involving obscure microbes studied by a cast of unknown German, Russian, and American observers. We learn as well of other integrated partnerships that fall short of symbiogenesis, such as grass-eating cows and wood-eating termites whose diets depend on enzymes supplied by gut-living bacterial symbionts. Overall, there is a wealth of absorbing and exciting evidence presented to give credence (to a point) to Margulis’s theory, including some aspects of Earth-as-Gaia. But, as Mayr indicates, there is no evidence for acquired genomes in the evolution of birds, for example, nor should “acquiring” genomes be confused with Lamarckian inheritance.
An exhilarating exposition of provocative if extreme ideas.