Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The emergence of the phenomenon of the existence of species probably contributed to acceleration of biological evolution, including its anagenetic components.While the evolution of asexually reproducing organisms can take place in arbitrarily small steps, the evolution of sexually reproducing species can progress only in larger steps (Bernstein et al. 1985).If a certain subpopulation of a sexually reproducing species is to differentiate into a new species, it must differ from the original species sufficiently significantly to compensate the disadvantage that a less numerous species has, if only because of worse conditions in searching for sexual partners or because of slower evolution of adaptive traits as a consequence of lower effectiveness of selection in small populations (see IV.4).This handicap does not exist amongst asexually reproducing organisms and thus they can undergo “pseudospeciation” without any great limitations.Most mutations that are fixed in the individual genealogical lines of asexually reproducing organisms cause only very small differences in their biological characteristics.Thus they remain exposed to approximately the same selection pressures, so that most evolutionary changes tend to be small and thus frequently reversible.If the conditions in the environment change cyclically or irregularly in time, the populations of asexually reproducing species change almost simultaneously and thus do not have time to accumulate a sufficient number of anagenetic changes that would assist in overcoming any valleys in the adaptive landscape and occupy other peaks in it.Asexually reproducing species can thus relatively easily attain local optima; sexually reproducing species react less willingly to selection pressure, but in time also occupy global optima in the particular adaptive landscape.