I was enjoying a couple of pieces of chocolate recently and as I was finishing up I began sneezing uncontrollably. I'm used to this, it happens frequently when I eat chocolate. I exclaimed to my friends that I was just expressing my Neanderthal genes. When pressed to explain myself, I claimed that I'd read it someplace before.

I wanted to verify what I learned since I have not had any genetic testing and can't say for certain that I have Neanderthal genes. I read several articles indicating that sneezing when eating dark chocolate was associated with the Neanderthals sequence. But I was starting to have the feeling that this was not all correct.

Digging deeper this is what I learned:

• According to 23andMe there are "135,171 Single Nucleotide Polymorphisms (SNP's) for which the derived allele (the "Neanderthal variant") is believed to have originated in Neanderthals and later entered the modern human population via interbreeding."
• The 'Dark chocolate sneeze' which affects about 25 to 30 percent of the population is on Chromosome 11. SNP rs11213819 is the identified Neanderthal variant. It has a signed effect of - 0.387 thus carriers of this Neanderthal variant are less likely to sneeze after eating dark chocolate.
• The brain initiates a sneeze through stimulation of the trigeminal nerve. I suspect that the evolutionary selection for sneezing was to rid the nasal passages of irritants such as dust and pollens. Unfortunately for us, some disease agents such as bacteria and viruses take advantage and disperse through our sneeze reflex. The dark chocolate sneeze has not been studied in as much detail as the photic sneeze reflex. In this reflex, overstimulation of the optic nerve by bright sunlight passes on a message to the trigeminal nerve leading to a sneeze.
• An acronym is a pronounceable word developed from the letters of some phrase or name which have become their own popular word. Well known examples include laser, radar and scuba. A backronym is like a reverse acronym where a phrase is made up to fit an existing word. This is sometimes done for serious reasons as in the phrase Amber Alert, but more often for comedic purposes. I'm not sure which category it fits into, but the photic sneeze reflex has been also been called the Autosomal Dominant Compelling Helioopthalmic Syndrome (ACHOO).

Here are my take-home lessons:

• Does chocolate make me sneeze? Probably yes
• Can I blame the Neanderthals? No
• Do I like chocolate? Definitely yes
• Pass the chocolate please....Achoo!

Link of interest: 23andMe Neanderthal Inference

An interesting aside, Karen Schrock writing in Scientific American tells us that Aristotle (4th century BCE) who apparently suffered from the ACHOO speculated that the heat of the sun on the nose led to the sneeze. In a very early demonstration of the scientific method Francis Bacon (17th century CE) covered his eyes in the sun and that prevented the sneeze, thus refuting Aristotle.