What makes you human? Is it the appearance? Intelligence? How they interact with other people? Even if you do pin point what you consider to be human, there will be others that disagree with you entirely, and might have a narrower view of what could be considered "human". For those that have a wider view, how far does this vision really go?
The more technology advanced we get, I always wonder how quickly people will accept alterations to their lives. For example, if we were dealing with robots that looked and acted like humans, would society be able to accept them as equals; or would something that is completely artificial be considers an other. This is where To Aru Kagaku no Railgun S comes in. Whether it is clones of Misaka or completely artificial Lifeforms like Febri, this anime puts a spotlight on people that consider these types of life insignificant.
Twin or Clone
When it comes to cloning, it is far more difficult to actually tell whether the clone are "naturally" born or born through science. You could essentially categorize a clone to being a twin, and that is what Railgun has done by calling those MISAKAs sisters. And if clones are indistinguishable from a twin, why are most of the scientist, and even Accelerator, treating these sisters as disposable trash?
Well, the sheer volume of MISAKAs being produced is one reason for the disconnect. Not only volume, but the way you can produce a few is a pretty simple task, which explains the number of MISAKAs roaming around. Now, this might be something that may swing some people in the opposite direction, where the scientist are, but you aren't looking at it in the right point of view.
If we look a humans, in general, you can say that there are a massive amount of people on earth -- that being around 7 billion people. Now, using the previous logic we can say that it is pretty easy to produce human life based on numbers alone. And if we compare numbers, the MISAKA sisters are around 20 thousand and that is only a small drop in an entire ocean of humans.
So if we really compare clones to humans, there isn't much of a difference genetically, physically, or psychologically.
Organic or Artificial
A bit farther down the man made life spectrum is completely artificial life. Unlike cloning, where the original genetic mapping starts from an organic life, artificial is made completely independent of any starting point -- beside the basic biologically knowledge of what homo sapiens are made of.
So really, the only difference we have to compare clones to completely artificial life is its genetics. The structure of their genes might look similar or differ entirely, but we still have two other factors that can be very much similar to a clone and human. It really only comes down to whether or not they look and act like a normal person is what is important -- and for the most part Febri and Janie do fit the description.
Human or Monster
The whole "acts like a duck, talk like a duck, then it is probably a duck", rings pretty true in this case. However, throughout Railgun S you can see humans act like a lot less "human-like", when it comes to the treatment of their "other". Even if the focus of the series wasn't really on this, it is still apparent that sometimes humans can be as much of a monster as the non-humans they think are.
You get what you give, but sometimes it is better to treat people as good as you want them to treat you, whether they are human, clone, artificial life, robot, what have you.