The experiments nevertheless showed that fertilization between two different species was not possible, because of the specificity of the carbohydrate moiety ZP3 glycoprotein (specific for a given species, the protein part being very conserved during the evolution) involved in the fertilization process. This specific recognition mechanism is especially useful for animals with external fertilization, as some fish or amphibians: the female lays her eggs in the middle, and the male comes to deposit his sperm.
