When I was in college I would sometimes have late night conversations with the guys in my dorm, and the discussion would random-walk in very strange directions. During one of these quasi-salons a friend whose parents were from Korea expressed some surprise and disgust at the idea of wet earwax. It turns out he had not been aware of the fact that the majority of the people in the world have wet, sticky, earwax. I’d stumbled onto that datum in the course of my reading, and had to explain to most of the discussants that East Asians generally have dry earwax, while convincing my Korean American friend that wet earwax was not something that was totally abnormal. Earwax isn’t something we explore in polite conversation, so it makes sense that most people would be ignorant of the fact that there was inter-population variation on this phenotype.
But it doesn’t end there. Over the past five years the genetics of earwax has come back into the spotlight, because of its variation and what it can tell us about the history and evolution of humans since the Out of Africa event. Not only that, it seems the variation in earwax has some other phenotypic correlates. The SNPs in and around ABCC11 are a set where East Asians in particular show signs of being different from other world populations. The variants which are nearly fixed in East Asia around this locus are nearly disjoint in frequency with those in Africa. Here are the frequencies of the alleles of rs17822931 on ABCC11 from ALFRED:
The expression of the dry earwax phenotype is contingent on an AA genotype, it has recessive expression. So in a population where the allele frequency of A ~0.50, the dry earwax phenotype would have a ~0.25 frequency. In a population where the A allele has a ~0.20 frequency, the dry earwax phenotype would be at ~0.04 frequency. Among people of European descent the dry earwax phenotype is present at proportions of less than ~5%. Because of recessive expression a larger minority of Japanese and Chinese should manifest wet earwax, though interestingly the ALFRED database indicates that Koreans are fixed for the A allele. In Africa conversely the G allele seems to be fixed.
