III.1 Mutations are the source of evolutionary innovations at the level of species
Genetic drift, molecular draft and, in most cases, also natural selection reduce the genetic variability in the population (see Chap. IV, V, VI).Mutation processesthat generate genetic variability act in the opposite direction.Mutations, changes in the structure of the genetic material, are the only source of variability and evolutionary innovation at the level of the species; in their absence, biological evolution would sooner or later stop.If more fundamental changes occur in the environment, organisms that would not be capable of undergoing mutation processes and thus of adapting to changes in the environment, would die out.However, at the level of individual populations, gene flow (see Chap. VII) and genetic recombination are the main source of evolutionary innovation.In fact, even in species without regular sexual reproduction, for example bacteria, in which recombination must occur with the participation of relatively ineffective processes of transformation and transfection, the recombination is responsible for the formation of new alleles 10x more frequently than mutations (Feil et al. 2000).