In absence of the title, i found this book to be fascinating and insightful to a lay-person. The descriptions of the sexual practices of other animals and creatures in opposition to humans was very revealing. However, the title of the book is a question, which i expected to be answered at some stage, and in a succinct form. In this, the book singularly fails. The author does not at anytime say "so why is sex fun? Because...xyz" It just doesn't happen.
I don't wish to detract from the very cogent arguments that are postulated, but the title remains unanswered, and for that reason i was left disappointed. Perhaps much like the unrequited orgasm, i was left wanting.
It's a pity, because Diamond is a very insightful writer - perhaps a bit doom and gloom if you read Collapse - but i really wanted an answer from him; i was begging from an answer, a succint answer that never came.
Otherwise a good read.