Answer:
Charlie and Algernon are very different, yet peculiarly similar.
Charlie, of course, is a human and has a much bigger emotional variation than Algernon. Charlie has desires for love, sex, connection and relationships. Algernon is a mouse, so he has the desire for food. We don't see him wanting anything that Charlie wants throughout the novel. We can see, at the beginning of the novel, that Charlie and Algernon are similar in their simple mindedness. They are both dull, even at Algernon's farthest mental capacity, because they are naive. Once again, Algernon is a mouse, so he cannot have the emotional capacity of a human. Charlie in the beginning, because he is special ed, he has about the same mental and emotional capacity as Algernon.
I hope this helps!
Laila