What is the theme in The Left Hand of Darkness by Ursula K. Le Guin?

Growth and development are recurring ideas. In establishing the basic facts of life on Gethen, this novel raises the fundamental question of "nature" versus "nurture": which cultural traits are learned and passed on from generations, and which are direct results of one's immediate surroundings? Since the people on this planet have no gender distinctions, their society is less restrictive about where citizens can go and what jobs they can take; the phrase "The king is pregnant" may sound strange to Earth ears because the associations that go with the word "king" are not the same as those that go with "pregnancy," but nobody on Gethen is fazed by the announcement.