Stranger in a Strange Land, Robert A. Heinlein
A man is born on Mars, he is the only survivor of the original expedition. He has been brought up by Martians and understands nothing of Earth's culture. In learning about humanity he starts teaching humans the Martian way of thinking. This is one of Heinlein's many books based around different ideas of relationships and sex. It had interesting ideas about what someone brought up outside human society might become. However overall this book felt old fashioned with the language and morality annoying me.
