What kind of earwax lurks in here?

An international team of researchers studied the genes of people from 33 populations across the world.

They found ethnicity affects which form of the gene people have, and therefore their earwax type.

And in Nature Genetics, they raised the unlikely possibility that earwax type could be linked to attractiveness, due to a link with body odour glands.

Earwax is secreted by the ceruminous apocrine glands.

This genetic analysis offers a method of studying how different populations moved around

Dr Sally Dawson, University College London

In both Europeans and Africans, the wet type completely dominates.

'Insect trap'

A 39-strong international team of scientists, led by researchers from the Nagasaki University Graduate School of Biomedical Sciences in Japan discovered the reason for the difference is a gene called ABCC11.

This gene controls the behaviour of a cell channel controlling the flow of earwax-altering molecules.

Any mutation in the gene can change the structure of the channel, which acts as a "gateway" into the cell, which then affects the type of earwax produced.

Further tests carried out in the lab showed cells with one ABCC11 mutation were less active secretors than cells with another.

The scientists, led by Koh-ichiro Yoshiura, suggest that a change in the channel probably first occurred in North-East Asia, and subsequently spread throughout Asia, as well as to native Americans and Inuit people with Asian origins.

They add that "the implications of earwax remain unknown".

But they suggest: "Insect trapping, self-cleaning and prevention of dryness of the external auditory canal are its plausible functions."

The link with attractiveness was mooted because studies on animals such as chimpanzees, orang-utans, dogs and mice have shown secretory products of apocrine, such as body odour, are produced by different glands from the same family as those which produce earwax.

Armpit odour has been linked to wet-type earwax.

And since apocrine glands are also found in the breast, there is a suggestion that a better understanding of how they work could offer clues about how breast cancer develops.

Dr Sally Dawson, a lecturer in molecular audiology at University College London, UK, told the BBC News website: "This research has shown that, as well as a physical condition, this genetic analysis offers a method of studying how different populations moved around - such as how people may have arrived in North America.

"And it is possible there is an association between earwax and other, major, conditions."

She added the researchers also claimed it was the first time a single letter difference in human DNA - called a single-nucleotide polymorphism - had been found to determine a visible genetic trait.