Most people are born with 12 ribs on each side of the body, making a total of 24 ribs. Despite the prolific misconception, this is the same for men and women.
This myth is often attributed to the biblical story of Eve being made from one of Adam’s ribs. One of the first people in Western science to challenge this idea was Andreas Vesalius in his 1543 book On the Fabric of the Human Body in Seven Books.
Ribs are crescent-shaped bones that protect the vital organs of the thorax while enabling the lungs to inflate to facilitate breathing. The first seven sets of ribs, known as “true ribs,” are attached directly to the sternum with cartilage. The following five sets are known as “false ribs”, three of which share a common cartilaginous connection to the sternum. The other two are also known as “floating ribs” because they are not attached to the sternum, but to the spine.
An illustration showing the anatomy of a rib cage.
Image credit: VectorMine/Shutterstock.com
A small percentage of the population does have fewer or more than 24 ribs for various reasons.
One such condition is known as a cervical rib, in which an extra rib arises from a vertebra in the neck. Some people with the condition will have a single rib on one side of the lower neck, while others might have a set of two ribs on both sides.
It doesn’t usually cause problems, although it is possible to remove the bone via surgery if it causes discomfort or complications. The most significant complication is known as thoracic outlet syndrome, where the nerves or blood vessels get squashed by the additional rib.
It’s estimated that between 0.5 and 1 percent of the human population has cervical ribs. The condition is genetic and suspected to be caused by mutations to Hox genes, a group of regulatory genes that determine where specific body parts, like limbs or organs, form during embryonic development.
It also occurs in certain animals. Studies have shown that a surprisingly high percentage of woolly mammoths had cervical ribs.
There are several other genetic conditions that can impact the number of ribs, including spondylocostal dysplasia, spondylothoracic dysplasia, and Goldenhar syndrome. Case reports also show that some people with Down’s syndrome can occasionally have fewer ribs.
People can also have ribs surgically removed for cosmetic reasons, namely to achieve a more defined waistline. However, it’s a dangerous procedure with a high risk of complications. There’s also the infamous urban legend about Marilyn Manson – although the less said about that the better.
