Excerpts:
OK, so what do we know from the games? All Pokémon lay eggs. Two Pokémon can create an egg together if they're of opposite genders and are members of the same "egg group" (loose categorizations of similar-ish Pokémon with names like "Fairy," "Mineral," "Bug," and "Field"). In the original games, you leave the two together at a Pokémon daycare and then come back to find an egg. In Pokémon Go, you just come across eggs with no explanation. Clearly, the game's designers did not want you to think how two Pikachus come together to make a third. And yet...
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With all this in mind, Gregory said that if he had to guess, most Pokémon probably have sex in one of two broad ways. Many Pokémon are bilaterally symmetrical, which Gregory defines as "two matched sides with a head at the front and a butt at the back," as well as a set of genitalia between their legs. Most bilaterally symmetrical animals engage in internal fertilization—a.k.a. penis-in-vagina sex. So essentially, any Pokémon that looks like it has legs, arms, and a head probably also has genitals, and probably uses those genitals in ways we're familiar with. In other words, maybe Strokemon is more accurate than its creators intended.
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Article author: Drew Millard, via VICE