An overview of speciation theory reveals an increasingly held view that many events leading to the origin of new species occur in transient, unstable populations. A transient, unstable population should be under stood as a fast episodic phase in a population subjected to genetic and environmental factors that tend to disrupt its cohesive, balanced genome architecure, thus enhancing its probability to produce a new species. Striking the core of Darwinian thought, some authors claim that these* processes may be non-adaptive. Among the environmental factors one may cite biotic (e.g. resource availability) and abiotic (e.g. temperature) stress conditions that break up the population stability producing random, unpredictable changes in population size, population trait distribution, breeding structure, inter- and/or intrapopulational hybridization, etc. Genetic factors consist of those events that induce rapid changes in genetic expression and/or that determine reproductive isolation, such as substitutions, insertions, deletions, duplications, transpositions, gross chromosomal rearrangements, recombination and, in general, any mechanism that changes the regulatory pattern of the organism or the balance of its meiotic system. Both kinds of factors are often intertwined in a complex net and may influence each other.

Our ever-increasing knowledge of whole genome sequences is unveiling a variety of structures and mechanisms that impinge on current evolutionary theory. The origin of species, the evolution of form, and the evolutionary impact of transposable elements are just a few of the many processes that have been revolutionized by ongoing genome studies. These novelties, among others, are examined in this book in relation to their general significance for evolution, emphasising their human relevance. The predominance of non-coding DNA in the human genome, the long-term adaptive role of so called "junk DNA" in the evolution of new functions, and the key evolutionary differences that define our humanity are just some of the controversial issues that this book examines in the context of Darwinian evolution. The author's principle intention is to show that whilst genomics is revealing new and previously unanticipated mechanisms and sources of variability that must be incorporated into evolutionary theory, there is no reason to dismiss the role of natural selection as the mechanism that sorts out these potentialities. In other words, this genome potential provides new possibilities (and also constraints) for evolution, but the realization of this potential is driven by natural selection.