Bones Variation
Accessory ossicles
Small extra bones, most often in the foot, that form when a growth centre never fuses with its main bone. They are harmless but can be mistaken for fractures on an X-ray.
Up to 1 in 5 feet
Variation
Normal structural differences between human bodies.
21 oddities.
Ears Variation
Attached and free earlobes
Some earlobes hang free and others join the head directly. Textbooks taught this as one gene, but a 2017 study found at least 49 genetic regions involved, and the two shapes blend into each other.
Both shapes are common
Mouth Variation
Bifid uvula
The uvula, the dangling flap at the back of the throat, is split into two lobes, in about 1 to 2% of people. On its own it is harmless, but in a baby it can be a clue to a hidden cleft of the palate.
1–2% of people
Bones Variation
Cervical rib
An extra rib above the normal top rib, growing from the lowest bone in the neck. About 1 in 100 people have one, and most never know.
About 1% of people
Bones Variation
Clinodactyly
A finger that curves sideways toward its neighbours, most often the little finger leaning toward the ring finger. Between 1% and 20% of people have it, and on its own it is harmless.
1–20% of people
Ears Variation
Darwin's tubercle
A small bump on the folded rim of the ear, which Darwin thought was the leftover tip of a pointed ancestral ear. Between 10% and 58% of people have one, depending on the population.
10–58% of people
Muscle Variation
Diastasis recti
A widening of the gap between the two halves of the six-pack muscle, seen in nearly every pregnancy and in some men. A bulge down the midline when you sit up is the usual sign.
Almost all pregnancies; about 1 in 3 women a year after birth
Eyes Variation
Distichiasis
A second row of eyelashes growing from the oil-gland openings along the inner edge of the eyelid. It is rare, mostly inherited, and Elizabeth Taylor was born with it.
Rare
Mouth Variation
Geographic tongue
Smooth red patches with pale borders that form a map on the tongue and move around over days and weeks. About 1 to 3% of people have it, and it is harmless.
1–3% of people
Eyes Variation
Heterochromia
Eyes of two different colours, or one eye with two colours, in fewer than 1 in 100 people. When it is present from birth it is almost always harmless.
Under 1% of people
Bones Variation
Hitchhiker's thumb
A thumb whose top joint bends back past 50 degrees, once taught as a simple recessive gene. Thumb angle is really a smooth range, and the genetics are not that simple.
24–36% of people
Bones Variation
Joint hypermobility
About 1 in 5 people have joints that bend further than usual, measured with a nine-point test called the Beighton score. For most people it causes no trouble.
10–25% of people
Bones Variation
Morton's toe
A second toe that looks longer than the big toe because the first metatarsal bone in the foot is short. It is common, and it is the foot shape seen on classical Greek statues.
3–22% of people
Muscle Variation
Palmaris longus
A thin tendon that stands out in the wrist when you press your thumb and little finger together. About 1 in 7 people do not have it at all, and they lose nothing.
Missing in about 15% of people
Muscle Variation
Plantaris muscle
A small calf muscle with a very long, thin tendon that medical students mistake for a nerve. Between 7% and 20% of people do not have it.
Missing in 7–20% of people
Ears Variation
Preauricular pit
A tiny hole in the skin just in front of the ear, present from birth, that leads to a short blind tunnel. It is harmless unless it gets infected.
0.1–10% of people
Body Variation
Situs inversus
All the organs in the chest and belly sit on the opposite side from usual, as in a mirror. About 1 in 10,000 people are built this way, and most are healthy.
About 1 in 10,000 people
Skin Variation
Supernumerary nipples
An extra nipple, usually small and flat, on a line running from the armpit to the groin. Between 1 in 500 and 1 in 18 people have one, and most think it is a mole.
0.2–5.6% of people
Mouth Variation
Tongue tie
A short or tight band of tissue under the tongue that holds the tip down, present in about 1 in 20 babies. Some cannot breastfeed well, but many grow up with no trouble at all.
About 5% of babies
Bones Variation
Torus palatinus
A hard bony lump along the midline of the roof of the mouth that grows slowly and is completely harmless. Many people find it by chance and worry that it is a tumour.
About 20% of people
Bones Variation
Webbed toes
Two toes joined by skin, most often the second and third, in about 1 in 2,000 to 3,000 babies. The toes usually work normally and many people leave them as they are.
About 1 in 2,000–3,000 births