From Charles Douglas Wehner:

Re: Scientists explore whether some apes shake heads for “no” (May 5): The story that Bonobos might mean “No” when they shake their heads is dubious. The reason is that the behaviour of shaking the head to say “No” is cultural, not genetic.

Eastwards of eastern Europe, it is usual to lift the chin to say “No”. This is like a reversed western “Yes”. To say “Yes”, the person repeatedly tilts the head from left to right - almost like the western “No”. These behaviours are common in Bulgaria, Albania, the Arabic countries, India and China.

My father went into a Turkish Bath in Bulgaria. After the heat, he had cold water thrown over him. The assistant offered more cold water. He shook his head and got another dousing. This went on until he understood that the “body language” had a reversed meaning in Bulgaria.