Ecological aspects of sexual reproduction

Sexual reproduction is one of the most interesting biological phenomena. No theory has ever entirely explained its wide occurrence among Eukaryotic clades despite its clear disadvantages (e.g. twofold price of sex). Theories can be divided into three groups according to the approach to solve this problem - molecular, genetic and ecological (environmental). Environmental theories are slightly preferred in the last decades and the opinion that the key to the sex enigma lies among them is widely accepted. Most of the environmental theories do not counter each other and there is possibility either to integrate them in several ways or presume that several of these theories might act simultaneously. According to theories, abiotically stable environments without biotic interactions (homogenous) should be suitable for and select for asexual species, whereas environments abiotically variable and rich in biotic interactions (heterogenous) should be suitable for and select for sexual species. The anagenetic phenomenon of punctuated equilibria and some of its explanations, e.g. P. R. Sheldon's Plus ça change hypothesis or J. Flegr's Frozen plasticity theory, also supports this division. There is a vast amount of empirical data supporting this division in ecological studies. Clearly homogenous environments..