If you decide to speak on "Humor and Wisdom," the easiest course would be to focus on a single example rather than trying to cover such a big subject in a short speech. The most obvious topic would be Mark Twain, who was noted for his humor and for his worldly wisdom. You could sprinkle your speech with quotations from Mark Twain's writings. Make your audience laugh. These quotes are easily accessible in the many quotations sites online. Another lesser-known writer you might sample in the quotes collections online is Stephen Leacock. E. B. White and his wife published a great book titled A Subtreasury of American Humor. It covers all the best American humorists from past to recent times, and provides samples of their writings. The book should be easy to find in your school library. You might look through it and pick out authors who make you laugh. You could make your speech a sort of sampling of American humor. E. B. White is now best remembered for his children's books Charlotte's Web and Stuart Little, but he was a distinguished essayist and a subtle humorist himself. Humor and wisdom often go together. Make it simple. Don't get buried under a lot of research.
Of the two, the second seems somewhat easier, as there is a great deal of concrete information available about the subject. There are a couple of different possible approaches you might take.
The first approach would be based on what is sometimes called orality-literacy theory, a body of academic research focusing on how primarily oral cultures (ones that have not invented writing), transmit knowledge across generations. In oral traditional cultures, historical information and other important cultural traditions are shaped into narrative form and performed. In such cultures, there is no real distinction between history and legend. Both are fused together as narratives of the past that can serve as guidelines for behavior.
The second possible approach is sometimes called "euhemerism", named after Euhemerus, a fourth century B.C. Greek who believed that all legends are actually distorted accounts of actual historical accounts.
In either case, you might shape your speech around how a specific event, such a the flood described in the Bible and Gilgamesh, could be accounted for within one of the two theoretical frameworks or both.