I like the title, "The Art of Being Human" but I think it would be best to stop there or "What It Means to Be", but I don't like them put together. The capitalization I would base on what is the most Artistic. I would do things in different ways depending entirely on the words themselves and what font you were going to use. In Wikipedia, I believe you will find something known as a secondary title, and this should be done altogether differently. The secondary title to be a much smaller font or not appear on the cover at all. I think Good Titles catch the eye and tickle the imagination. Two good titles do not make one good one, but only my opinion. Either one of these is great. If you are set on both I would make one of them a secondary title and place it below the primary in smaller font. How about, "What It Means To Be"
"The Art Of Being Human" in smaller font
or the other way around? Best of luck to you in this endeavor. Candlelight8