Even before the publication of Darwin's Origin of Species, the perception of evolutionary change has been a tree-like pattern of diversification - with divergent branches spreading further and further from the trunk. In the only illustration of Darwin's treatise, branches large and small never reconnect. However, it is now evident that this view does not adequately encompass the richness of evolutionary pattern and process. Instead, the evolution of species from microbes to mammals builds like a web that crosses and re-crosses through genetic exchange, even as it grows outward from a point of origin. Some of the avenues for genetic exchange, for example introgression through sexual recombination versus lateral gene transfer mediated by transposable elements, are based on definably different molecular mechanisms.
However, even such widely different genetic processes may result in similar effects on adaptations (either new or transferred), genome evolution, population genetics, and the evolutionary/ecological trajectory of organisms. For example, the evolution of novel adaptations (resulting from lateral gene transfer) leading to the flea-borne, deadly, causative agent of plague from a rarely-fatal, orally-transmitted, bacterial species is quite similar to the adaptations accrued from natural hybridization between annual sunflower species resulting in the formation of several new species. Thus, more and more data indicate that evolution has resulted in lineages consisting of mosaics of genes derived from different ancestors. It is therefore becoming increasingly clear that the tree is an inadequate metaphor of evolutionary change. In this book, Arnold promotes the 'web-of-life' metaphor as a more appropriate representation of evolutionary change in all lifeforms.
New insights into the genetics, genomics, and ecology of hybrids have created a need for universities to include this topic in their study programmes in ecology and evolution.
Preface; 1. History of Investigations; 2. The Role of Species Concepts; 3. Testing the Hypothesis; 4. Barriers to Gene Flow; 5. Hybrid Fitness; 6. Gene Duplication; 7. Origin of New Evolutionary Lineages; 8. Implications For Endangered Taxa; 9. Humans and Associated Lineages; 10. Emergent Properties; Glossary; Reference; Index
...one of the strengths of this book is that the author's argument does not succeed or fail on the example of this single taxon, nor does he use exclusively botanical examples. Indeed, I recommend his interesting interpretation of the temporal fitness variation and relative abundance of between-species hybrids in Darwin's finches...[..] I very much liked the organization of this book and the author's placement of the discussion of the emthods early in the monograph. This helped set the stage for the latter presentation and interpretation of data...[..] this chapter and the examples in it provide a solid introduction to the logic of monograph. In an important way, this mehtodological discussion also usefully seperates the observational question, "Does in occur?" from the more contentious, interpretive question, "What does it mean"...[..] I recommend it highly. Michael J. Wayde Evolution Through Genetic Exchange represents a compelling argument for a paradigm shift in evolutionary biology, in which the Tree of Life is replaced conceptually by a Web of Life that connects all living organisms and their genomes. The Quarterly Review of Biology