Thanks to millions of years of evolution, the human body has become well versed in its developmental processes. Most of the time, it gives us the correct number of organs and structures that we need to function. But sometimes, hiccups in this process mean people end up with extras.

Accessory teeth, fingers, toes and nipples are actually surprisingly common.

Up to 1% of the population are born with extra fingers or toes, while around 1% of people are born with additional teeth. Both of these phenomena are more common in men – particularly extra digits, which are twice as common in males.

Approximately 6% of people have an extra nipple. These can appear anywhere along the line that runs from the armpit to the groin – known as the mammary ridges or milk lines. As with extra teeth and digits, supernumerary nipples are more common in men, but it’s unclear why. They also tend to appear on the left side of the body.

But these aren’t the only places that extra body parts can appear. Some people are born with extra bones, organs or genitalia they might not even be aware they have.

Supernumerary ribs are typically seen in two places: the neck or the lumbar region (lower back). An estimated 1% of the population has an extra rib – though when it comes to an extra neck rib, it could actually be closer to 4.5%. The extra rib can occur on one or both sides of the spine.

An extra rib usually causes no problems and is only........

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