Frankenstein and the Definition of Human
You don't have to go very far to find a scientific definition of 'human'. In fact, Merriam-Webster says that the adjective 'human' is of relating to, being, or characteristic of humans; having human forms or attributes. For most, the defining of this term would end here, but through such works as 'Bicentennial Man', 'Counting Cats', and Frankenstein we learn that the definition cannot, must not, end there. To be human is to have all of the characteristics and something more. Call it self-awareness if you like or a soul if you prefer, but it's all the same.
In 'Bicentennial Man', Andrew starts out imitating human emotion though action as in this passage on page 248: "...and Andrew was fond of them, too. At least the affect they had upon his actions were those which in a human being would have been called the result of fondness." However by the end of the story his emotions are entirely his own and very real, which can be seen on page 286 when he vocalizes his distress in the fact that the congresswoman chose not to abandon him to save her career. This is what makes Andrew truly human, even compared to his 'final' sacrifice, the part of him that has come to realize that he isn't just acting out the emotion any more, he really is feeling these sensations.
Although shorter and not as easily seen this same thing can also be found in 'Counting Cats' the emotional progress isn't as apparent, but it is suggested. This story is more emotion by action than by thought. Their words go round and round in bantering circles, that are sometimes difficult to follow, but their actions are entirely straight-forward. His acceptance of her books on page 267 is one example of this and makes his feeling more apparent than any words could truthfully express. So, once again we see that this is what makes him 'human', the little things that most might not even notice.
In Frankenstein, the Monster's emotions rule him entirely. Within him...