As much philosophy as phenomenon, memetic exchange is the process by which life on Yuriba reproduces. The memes involved in this instance consist of the spiritual and mental makeup of the partners: the translation of the native term into the English "meme" is somewhat inaccurate as the Yuriban concept of meme does not involve cultural components. When memetic exchange occurs, the spiritual and mental substances of two individuals are combined to form the spark of a new physical life. Memetic reproduction does not occur solely between sentient beings, but also between animals, and even plants. Moreover, even immigrants to Yuriba can produce by memetic reproduction; the process appears to be a natural law of the island rather than a property of the native population.
Memetic exchange is only possible when both partners desire for reproduction to occur, meaning that the vast majority of Yuriban pregnancies are deliberate choices. However, this desire need not to be conscious – the closest Yuriban equivalent of an 'unplanned pregnancy' is one in which one or both partner's subconscious desire for children is so strong that it takes effect without deliberate choice. Furthermore, memetic exchange can only occur between spiritually and mentally compatible individuals. (At least, spiritually and mentally compatible at the time of conception.) Thus, while a female of a non-Earth native race could breed with an Earth native if they had similar outlooks, the memetic exchange would fail if the mental structure and thought patterns were strongly divergent from one another. In a related vein, memetic exchange is not possible between males and females because of fundamental differences in the thought process. However, males can of course reproduce with one another via memetic exchange. Evidence suggests that simple life forms are compatible with fewer individuals, explaining why, for example, native plant species usually only reproduce within themselves.
While sexual contact greatly enhances the odds of an effective memetic exchange occuring, due to the physical and emotional affects of arousal lowering mental barriers, it is not actually necessary. Either partner (or, more rarely, both) can become pregnant during the same exchange; the choice of which parent bears the child lies in the same conscious and subconscious factors as the initial exchange. Despite the fact that the memetic reproductive model does not rely on a regular monthly ovulation, species on Yuriba that would elsewhere still undergo menstruation or estrus. The grounds are at present scientifically unclear. One popular theory is that it is related to the deity Engetsu's governance over cycles; another, that it is merely a holdover from the ancestor species of modern Yuriban lifeforms.
The exact process by which memetic information translates to the physical level is unclear. It is likely to be catalyzed, if not fueled, by the high magic levels common on the island. Children tend to display traits of both parents physically as well as mentally, making it clear that the genes do not derive solely from the parent that bears the child.