On the "origin" of natural selection by means of speciation

A new model of evolution of adaptive traits in sexual species is suggested. As the expression of most phenetic traits is codetermined by many genes an d the influence afa gene on the phenotypic trait is often gene-context spec ific, the heritability of phenetic traits in outbreeding populations is oft en low. Also the effect of expression of a single trait on biological fitne ss is often context specific being determined by the presence and level of expression of other phenetic traits. Because of the low heritability of phe netic traits and of biological fitness the potential for adaptive evolution ary change by means of natural selection is very limited in sexual species. However, most mechanisms of speciation lead to drastic reduction of geneti c variance in the new species. In the absence of genetic variance genetic c ontext for a new mutation is always the same and the heritability of phenet ic traits and of biological fitness increases. After a renewing of genetic variance by mutation processes the heritability of traits and fitness again decreases. In the history of any sexual species a transient period of evol utionary plasticity, in which the species can respond to natural selection and evolve new phenetic traits is followed by a long period of evolutionary stasis in which the species accumulates changes mostly by genetic drift an d molecular or meiotic drive.