A GENETIC study of more than 3000 people worldwide has solved one of life’s mysteries: why some people have dry earwax while others exude a brown sticky goo.European and African people tend to have wet, sticky earwax while dry wax is common among people with east-Asian ancestry.To find out why, Japanese researchers genetically tested 64 Japanese people with the dry type and 54 Japanese people with the wet type. They found that, of the 3 billion pairs of letters that make up the human genetic code, a variation in just one letter determined the type of wax a person was born with.Further tests were carried out on 3250 people from 33 ethnic backgrounds. They revealed that the genetic variation responsible for dry wax was present in Koreans and northern Han Chinese, but not in Africans or African Americans.In other populations, this genetic variation became increasingly less common the further south or west of north-east China the ethnic group originated, with Solomon Islanders, the French and Hungarians having a low frequency. The researchers, led by Koh-ichiro Yoshiura of Nagasaki University, said the findings suggested the mutation for dry earwax arose long ago in north-east Asia and spread as its people migrated to other countries.The mutation’s high frequency in native Americans “may reflect their ancestors’ migratory waves from Siberia over the Bering land bridge to the American continent”, Dr Yoshiura suggested.Earwax helps to trap insects, clean the ears and keep them moist. The advantages of dry earwax, if any, are unknown. People with wet wax, however, tend to sweat more and have more body odour, the researchers said.This suggests that dry earwax may have become more commonplace because of its association with reduced body odour, which in turn might make people more attractive to a mate in the cold, cramped living conditions of ancient north-east Asia.The findings, published today in the journal Nature Genetics, represent the first example of a tiny genetic variation, known as a single nucleotide polymorphism, being linked to a visible physical trait.
