It is remarkable that in the comments here, present day norms are accepted as natural, even though they were different in recent history, and are bound to be different in the near future as much as the 40 hour work week might become 30, and flexible work hours might lead to adoption of objectively healthier sleep patterns than what industrial society has imposed. Diet, alcohol consumption, coffee drinking, smoking, sleep, the prevalence of prostitution, education, etc., have all changed faster than any claim of being "natural' could set in just by being the current norm.

So much in-the-box thinking.