Many critics and readers interpret this novel as a work expressing a basic human equality, regardless of race, age or legal status. Jim and Huck are equally human and have an equal right to freedom and happiness.
Many critics agree...seeing the novel itself as a critique of the racism expressed by its narrator, Huck.
There is some debate about this as a theme in the novel, however.
The crux of the controversy is whether or not the novel presents an indictment of racism or simply reflects the generally accepted racist attitudes of the time period in which it was written.
Considering this debate, we can turn to more definitive themes in the novel regarding human nature.
Gullibility is certainly a principle characteristic of every character in the book. Huck, Jim, the King, the Duke, Pap, and Aunt Sally, along with essentially everyone else presents an image of gullibility, willing to believe lies, easily cheated, and easily persuaded to change their minds.
Examples of this human trait abound.
Being gullible, as a trait, can be extended and interpreted as a larger commentary on the whimsy of human belief. Religion (as seen at the dinner table and at the revival in the novel) is shown to be another arena where people are fooled. (The King swindles an entire crowd of revivalists.)
Huck's difficulty in coming to terms with his own morality can be seen as a symptom of society's whimsical or fanciful beliefs. The moral sense that he has been instructed to uphold fails to provide Huck with a practical sense of what is truly right and wrong.
The gullible protagonist too has been influenced to believe in ideas that he cannot consistently apply.