When a new noun arises in German, who decides the gender of the noun?
Many nouns are formed by connecting several words, in that case the new word will have the gender of the last word. When some new word is formed from scratch germans turn to their thrusted institution the Duden Dictionary which has a prescriptive nature. http://en.wikipedia.org/wiki/Duden For more on prescriptive nature of languages: http://en.wikipedia.org/wiki/Prescription_and_description
This. And often the ending of a word tells you a lot. -ung for example is most often 'die'. Verbs which become nouns are mostly in their infinitive form and/or ending with -en. Those are mostly 'das', das Gehen, Laufen, Gären, Sprechen, Bewegen. -chen and -lein indicate a belittlement which is always 'das'. Mädchen, Häuschen, Kätzchen. -keit and -heit lead to 'die'. Männlichkeit, Heimlichkeit, Bosheit, Gelegenheit.