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Genetics of Darwin's tubercle
Summary
You might have a small bump on the inside of your upper ear, known as "Darwin's tubercle" or "Darwin's bump," and you may have heard that Darwin's tubercle is a dominant genetic trait. This is not true! Family studies show that Darwin's tubercle is not a simple genetic trait. Don't worry if your family includes two parents without the tubercle and a child with it, and if you're a teacher, don't use Darwin's tubercle as an example of simple genetics.
Are there two kinds of ears, with or without Darwin's tubercle?
Darwin's tubercle is a small bump on the inside of the rim of the upper ear (not to be confused with a small bump on the outside of the rim, sometimes called a "satyr's peak" [Schwalbe 1891]). It ranges from a very slight thickening of the rim to a prominent bump (Hildén 1929). Where to draw the line between "slight thickening" and "no bump" is arbitrary; there's a continuous range of variation.
Some people have a bump on just one ear; Hildén (1929) surveyed a large number of Finnish schoolchildren and found that 33% had a bump on both ears and 28% had a bump on one ear. Ruiz (1986) found that 2% of Spanish adults had a bump in both ears and 6% had a bump in just one ear; the much lower numbers than in Hildén (1929) may be because they used different criteria for what to count as a Darwin's tubercle.
Family studies
Quelprud (1936) looked at presence (P) and absence (A) of Darwin's tubercle in a large number of German families. Some individuals had a bump on just one ear; including them in P, the results were:
| Parents | P offspring | A offspring | Percent P |
|---|---|---|---|
| P×P | 88 | 59 | 60% |
| P×A | 101 | 60 | 63% |
| A×A | 22 | 27 | 45% |
There are somewhat more A offspring from A×A matings than from P×P or P×A matings, suggesting that there is some genetic influence on the trait. However, if P really was caused by a dominant allele, two parents without Darwin's tubercle could not have a child with the tubercle. The large number of P offspring from A×A matings, and the large number of A offspring from P×P matings, are completely inconsistent with the simple genetic model of one gene with two alleles.
The only other family study that I'm aware of is Beckman et al. (1960), who found the following:
| Parents | P offspring | A offspring | Percent P |
|---|---|---|---|
| P×P | 1 | 3 | 25% |
| P×A | 10 | 28 | 26% |
| A×A | 14 | 44 | 24% |
These data are also inconsistent with the simple two-allele genetic model. They even suggest that there may not be any genetic influence on the trait at all.
Twin studies
Quelprud (1936) looked at Darwin's tubercle in identical twins. He found 58 pairs of twins where both were P and 32 pairs where both were A. There were 26 pairs of twins in which one twin had a Darwin's tubercle on one or both ears, while the other twin did not. If Darwin's tubercle was entirely determined by genetics, identical twins would be identical; therefore whether a person has Darwin's tubercle depends in part on developmental accidents or other environmental influences, not just genetics.
Genome studies
Adhikari et al. (2015) looked for associations between Darwin's tubercle and over 670,000 single nucleotide polymorphisms (SNPs) in over 4900 people . They only looked at the right ear, and they subjectively divided ears into those with no tubercle, those with a small tubercle, and those with a large tubercle. They found weak associations with two SNPs, one on chromosome 3 and one on chromosome 6. This suggests that there may be some genetic influence on Darwin's tubercle, but if so, it's not a single gene.
Further research
There haven't very many studies of Darwin's tubercle, but it seems clear that it varies continuously instead of being a simple presence/absence trait, and that it's not controlled by a single gene. I can't think of any reason to do any more research on it.
References
Adhikari, K., et al. (37 co-authors). 2015. A genome-wide association study identifies multiple loci for variation in human ear morphology. Nature Communications 6: 7500.
Beckman, L., J.A. Böök, and E. Lander. 1960. An evaluation of some anthropological traits used in paternity tests. Hereditas 46: 543-569.
Darwin, C. 1871. The descent of man and selection in relation to sex. London: John Murray.
Hildén, K. 1929. Studien über das Vorkommen der darwinschen Ohrspitze in der Bevölkerung Finnlands. Fennia 52: 3-39.
Quelprud, T. 1936. Zur erblichkeit des darwinschen höckerchens. Zeitschrift für Morphologie und Anthropologie 34: 343-363.
Ruiz, A. 1986. An anthropometric study of the ear in an adult population. International Journal of Anthropology 1: 135-143.
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This page was last revised October 26, 2026. ©2026 by John H. McDonald. Content is available under the Creative Commons Attribution-Noncommercial license.