Asked by: Ralph Talbot, Chichester
Just two. The most common, wet earwax, evolved as a way to remove dead skin cells from your ear canal. Earwax is 60 per cent skin, with various different oils binding it together in a brown lump.
But there is a recessive gene mutation that results in a different mix of oils, giving grey and flaky earwax. This dry earwax is common among the Japanese and Native Americans. Coincidentally, having dry earwax also means you produce less armpit odour.
Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.