Contains Multitudes by Ben Burgis
This is one of the best short science fiction stories I’ve read in a long time; the consequences of an alien invasion on an alternate earth with its own alternate history. The humans were given a choice: be destroyed utterly, or to allow infant aliens to merge with the children. They don’t really have much of a choice – the theme here is survival; the aliens are obviously doing this to survive, because for some reason they cannot raise their next generation without outside help anymore. This arrangement, they said, is only temporary - until both the aliens and human are grown up; after which they would presumably part ways.
I also found it interesting that the humans aren’t hosting the aliens – they become two entities in one body. Therefore, when the alien and the human have differences in taste – like any two different people often do - one loves coffee, for instance, and the other abhors it – they drink it, to the relish of one and the antipathy of the other. Henceforth, if I find any good full-length novels with a similar concept of duality, it’s going into my to-read list :D