The man with the cap is a writer; the man without the cap is a book critic.
The man with the cap is Christopher Ryan, the coauthor of a very important book called Sex at Dawn: The Prehistoric Origins of Modern Sexuality. The reason why Sex at Dawn is an important work is it convincingly links human sexuality with human sociality, the most developed form of mammalian sociality. And the world has yet to see a human being who is not a product of this form of animal sociality. Ryan's reading of this book happens in a few hours.