That's interesting. However, here is where the exact amount of connectivity does matter, and probably it is important also which part of the brain is connected. If the amount of communication in each of the two brains is orders-of-magnitude larger that the communication between two brains, the development of two personalities is natural. From what I learned from this article, only low-level sensory signals are transmitted through the channel that the girls share. Is it due to the amount or to the type of the connecting neurons or due to the part of brain where it is connected?..

Since time passed [since our communication] I had also another thought about all this. While natural sources of information (eyes, ears,...) is what we are doing for years, a different type of device (say, external memory or a direct connection to someone else's brain) may be more difficult to handle. Probably genetic evolution is not absolutely necessary; the "cultural" development of concepts around such connections can replace it. However, we may still need several generations to learn how to use and even feel it properly, because proper hormones have to be released, etc.

On the other hand, if two mature humans are connected so strongly that they couldn't distinguish whose memory it is and whose feeling it is, it will almost certainly create fatal madness --- just because we are incapable of handling this in our "culture", no experience, no learning how to handle it from the childhood, etc.

All this makes real experiments even more difficult.