There are many factors that control the process of Sperm (Maturation, Ejaculation, Capacitation, Migration, Motility, Vitality, Chemotaxis/Thermotaxis etc.), Egg (Ovulation, Maturation, Chemotaxis, Recognition, Penetration, Migration etc.) and Embryo (Fusion, Nutrition, Cell Division, Migration, Implantation etc.). Some of these factors specifically reside on the sperm surface and are acquired by the sperm as it matures through spermatogenesis and on its way through the Testis, Epididymis, Vas Deference and Seminal Vesicle. These factors are secreted by the tissue into the tubes through which the sperm journeys and matures..
Whereas fertilization occurs in ~95-100% of intercourses occurring around the ovulation time for small-medium mammals, the efficiency reduces dramatically when it comes to Primates and especially for Humans where the rate is between 15-30% (which means that if everything is OK, only one in every 3-8 attempts around ovulation will end up in successful fertilization and a pregnancy).
It has been observed that whereas some of the fertility related proteins, peptides and factors are highly conserved through evolution, some of these factors can diverse in structure/function/sequence from species to species and in some cases, some factors could be species specific. There are observations of such factors that were shortened/changed through evolution and in some cases even altered their function dramatically.