ABO phenotype protected reproduction as it is based on fucosylations.

The molecular biological relationship between human fertility and ABO(H) blood group phenotype formation becomes evident with the rare (Oh) or <i>Bombay</i> blood type, which based on the history of his own family, Charles Darwin would have interpreted as resulting from reduced fertility in consanguinities. In its native form, the <i>Bombay</i> type occurs in individuals with an extremely rare genotype (h/h;se/se), by which the fucosyltransferases FUT1 and FUT2 are not produced due to point mutations. These enzymes, encoded on chromosome 19, are epistatically connected with the A and B allelic glycotransferase functions encoded on chromosome 9, while the fucosyl residues provide the functional-structural basis for the formation of any ABO(H) phenotype on the cell surface or in secretions and plasma proteins. Immunoglobulins are also heavily fucosylated, and via developmental variation of the positions between the cell surfaces and the heavy chains of immunoglobulins, fucosyl residues appear to augment or reduce antibody-mediated cellular cytotoxicity involving physiological anti-self-reactivity; moreover, by regulating the assembly and intracellular signaling of precursor B cell receptors, the core fucosylation of immunoglobulin heavy chains represents a key mechanism in clonal selection. In fact, the seminal plasma of leucospermic infertile men has been reported to exert high levels of poorly core-fucosylated IgG. Consequently, in <i>Bombay </i>type individuals, the non-somatic glycosylation processes of embryogenic stem cell-to-germ cell transformation, which involve the modification and <i>O</i>-fucosylation of epidermal growth factor (EGF), are most likely exposed to metabolic competition with multiple glycosidic sites of poorly fucosylated, glycan-depleted immunoglobulins that might promote increased anti-self-reactive cytotoxicity.