Final answer:
Twain's literature often critiqued societal norms and hierarchies, including the acceptance of slavery in pre-Civil War America.
Step-by-step explanation:
The author's conclusion about what Twain says about the human race is not explicitly stated in the given information. However, based on the information provided about Twain's literature and themes, it can be inferred that Twain often used his works to critique societal norms and hierarchies, including the acceptance of slavery in pre-Civil War America. Twain's use of satire and humor may suggest a critical view of the human race's tendency to uphold unjust systems.