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

If somatic cells fulfill the function of sex cells, as for unicellular organisms, then only functional differentiation of mating types usually remains.However, if the organisms form a specialized type of sex cell, gametes, for sexual reproduction, then functional anisogamy is generally followed by morphological anisogamy, differentiation of sex cells into microgametes andmacrogametes.As their names indicate, microgametes are smaller and usually mobile, while macrogametes are usually many times larger and frequently immobile.In the typical case, the microgamete contributes only its genetic material to the formation of the zygote, while the macrogamete provides both its genetic material and cytoplasm.A number of hypotheses have been formulated to explain morphological differentiation of gametes into just two types (Matsuda & Abrams 1999).