Darwin's tubercle is a congenital ear

Ear

The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....

 condition which often presents as a thickening on the helix

Helix (ear)

The prominent rim of the auricula is called the helix. Where the helix turns downward behind, a small tubercle is frequently seen: the auricular tubercle of Darwin....

 at the junction of the upper and middle thirds. The feature is present in approximately 10.4% of the population. This acuminate nodule represents the point of the mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

ian ear.

This atavistic

Atavism

Atavism is the tendency to revert to ancestral type. In biology, an atavism is an evolutionary throwback, such as traits reappearing which had disappeared generations before. Atavisms can occur in several ways...

 feature is so called because its description was first published by Charles Darwin

Charles Darwin

Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

 in the opening pages of The Descent of Man, as evidence of a vestigial feature indicating common ancestry among primates. However Darwin himself named it the Woolnerian tip, after Thomas Woolner

Thomas Woolner

Thomas Woolner RA was an English sculptor and poet who was one of the founder-members of the Pre-Raphaelite Brotherhood. He was the only sculptor among the original members....

, a British sculptor who had depicted it in one of his sculptures and had first theorised that it was an atavistic feature.

The gene for Darwin's tubercle is inherited in an autosomal dominant pattern, and has incomplete penetrance

Penetrance

Penetrance in genetics is the proportion of individuals carrying a particular variant of a gene that also express an associated trait . In medical genetics, the penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms...

, meaning that those who possess the gene will not necessarily possess the ear tubercle.