un articulo que me ha echo pensar en las cosas que tenemos en común los humanos. Incluso los que somos de culturas diferentes:
Why do we nod our heads for "yes" and shake them for "no"? via Digg

No less a personage than Charles Darwin looked into it and wrote up his findings in a book called The Expression of the Emotions in Man and Animals (1872). Darwin was interested in finding out whether there were universal gestures and expressions, so he sent out a questionnaire to missionaries and whatnot that, among other things, asked what gesticulations the locals used to convey "yes" and "no."
[...]
Still, cultures ranging from the Chinese to the natives of Guinea nod and shake their heads like we do, leading Darwin to believe that the gestures were innate to some extent. He noticed that when babies refused food they almost always turned their heads to the side, whereas when they had worked up an appetite they inclined their heads forward in a nodding gesture.

como extra, el articulo habla de culturas en las estos gestos significan cosas diferentes:

• Certain Australian natives, when uttering a negative, "don't shake the head, but holding up the right hand, shake it by turning it half round and back again two or three times."
• The Abyssinians said "no" by jerking the head to the right shoulder and making a slight cluck, while "yes" was expressed by the head being thrown backwards and the eyebrows raised for an instant.
• The Dyaks of Borneo supposedly raised their eyebrows for "yes" and slightly contracted them, "together with a peculiar look of the eyes," for "no." Eskimoes nodded for "yes" and winked for "no."
• Ins Bulgaria a nod means no and a shake means yes. One shudders to think of the implications this has for cross-cultural dating in that country. The Turks are almost as confusing--they say "yes" by shaking their heads from side to side, and "no" by tossing their heads back and clucking.
• Head-tossing for "no" is also common in Greece and parts of Italy, such as Naples, that were colonized or heavily influenced by Greeks in ancient times.