Hiccups are a weird phenomena. They are a combination of two involuntary actions - firstly a rapid inhalation of breath followed 35 milliseconds later by the glottis at the back of the throat suddenly closing off our airway.
Our normal breathing is controlled by a "central pattern generator" in a small region of the brain stem close to the boundary with the spinal cord. A signal is sent along the vagus and phrenic nerves resulting in a rhythmic contraction of muscles in chest, diaphragm and throat.
These nerves branch off right at the top of the spinal cord and follow a convoluted path through the chest cavity. Any spasm in these nerves result in the first part of a hiccup.
But what about the second part - the snapping shut of the glottis with the resulting comical squeak - where did that come from?
It turns out that the pattern generator responsible for hiccups in humans is virtually identical to one in tadpoles.
Fish breathe by extracting oxygen from water in their gills. Amphibians breathe by extracting oxygen from air in their lungs. Tadpoles, who metamorph into frogs, have gills and lungs and can do both. Our evolutionary ancestors who emerged from sea onto dry land also had a combination of lungs and gills.
When tadpoles breathe with their gills they inhale water into their mouths and then the pattern-generator in their brain stem rapidly closes the glottis to block the path to the lungs and forcing it out through the gills. This involuntary sequence still exists in the wiring of the most ancient part of our brains and when it is accidently triggered gives us hiccups.
In experiments, gill-breathing in tadpoles can be interrupted by increasing the level of CO2 or by stretching the wall of the chest. The tadpole then reverts to lung breathing. Hiccups can be interrupted in the very same way. Breathing into a paper bag increases the CO2 levels and holding a deep breath stretches the diaphragm. Your best chance is to stop the bout in the first ten hics otherwise it is likely to last an average of sixty.
Spare a thought for Iowa resident Charles Osborne who started hiccupping in 1922 and didn't stop until February 1990.
Evolution is a Fact 1 - 30 Index...
#31 Ten Questions For Creationists ...
The basic facts about reality covered so far pose an impossible challenge to creationism.
#32 Sexual Selection
How female mating preferences led to some of the most remarkable features of living things.
#33 A Tale About Tails
Human embryology reveals our primate history.