A popular belief about this has been shown to be wrong.
11 oddities.
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.
Turning both eyes inward toward the nose on purpose. Nearly everyone with normal two-eyed vision can do it. Your eyes will not get stuck that way.
Some children can keep a detailed picture of an image in view for a short time after it is taken away. The ability fades by the teenage years. A true photographic memory in adults has never been confirmed.
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.
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.
Pulling or bending a finger joint until it pops. Between 25% and 54% of people do it out of habit. The sound is a gas bubble forming in the joint fluid, and it does not cause arthritis.
About 1 in 60 people feel a touch on their own body when they watch someone else being touched. The brain system that mirrors other people's actions appears to be turned up too high.
Fingertips and toes wrinkle after 5 to 15 minutes in water. This is not the skin soaking up water. It is the nervous system shrinking the fingertip on purpose, and the wrinkles may improve grip when wet.
Most people have three kinds of colour-sensing cone. A few people have four. In theory they can tell apart colours that look identical to everyone else. Confirmed cases are extremely rare, and online tests cannot detect it.
In a room that absorbs almost all sound, you hear your heartbeat, your blood, your breath, and a high ringing from your own inner ear. True silence is not possible for a living person.
Between 65% and 84% of people can curl the sides of the tongue up into a tube. For decades it was taught as a simple one-gene trait. It is not.