Pokémon breeding is the most complex and mysterious branch of Pokémon research. While it is well known that Pokémon lay eggs, even mammalian species that should give birth to live young, the process by which this is done is still undergoing intensive research and debate. The primary reason for this debate is because several Pokémon that should be physically unable to breed, such as the infamous pairing of Skitty and Wailord, are still somehow able to produce off spring.
It has been proven beyond refute that the offspring of two Pokémon will always belong to the species of the female, unless a Ditto is involved, in which case the infant will belong to the species of the second parent. Researchers have never been able to witness an act of physical reproduction between Pokémon, suggesting that Pokémon reproduce via external fertilization. The female Pokémon, or Ditto, will lay an egg belonging to their respective species. The Pokémon inside the egg is a blank slate, essentially an insentient shell. It is then speculated that the male Pokémon will release a portion of his Extracted Xenotransplantation Percentage onto the unfertilized egg, granting the offspring sentience. Evidence for this theory is given in how Pokémon can be born knowing techniques that are far more advanced than their own Extracted Xenotransplantation Percentage levels would suggest, provided that the male parent has sufficient amounts of energy himself.
A Pokémon egg has several cycles that reflect upon the development of the Pokémon inside. These cycles are made up of "steps" which dictate the length of time a Pokémon takes to hatch. A single "step" is equal to a half hour of time, while a cycle lasts approximately five and a quarter days.
For example, a Magikarp takes 1.530 "steps" to hatch, comprising six developmental cycles. This means that the time between when a Magikarp egg is laid and when it hatches is approximately thirty-one days and twenty-one hours.