Finger length linked to aggression, musical ability, sexual orientation.
Published September 7, 2011
Is your ring finger longer or shorter than your index finger? The reason for the difference is in our hormones, a new study in mice shows for the first time.
Before birth, the sex hormones estrogen and testosterone control genes that in turn dictate finger length, the study found. Like us, mice naturally have both hormones in their bodies. (Get a genetics overview.)
As a result, most men have ring fingers that are longer than their index fingers, and the reverse is true in women.
Differences in finger length have been repeatedly linked to a range of human traits, from aggression to musical ability to sexual orientation. There are also connections to health problems such as autism, depression, heart attacks, and cancer.
“It’s difficult to look at an adult or a newborn child and determine what was happening during their embryonic development,” said study leader Zhengui Zheng, a developmental biologist at the Howard Hughes Medical Institute in Florida.
“But the discovery that digit proportions reflect the prenatal hormonal environment helps us to explain all those correlational studies,” said Zheng, who works in the laboratory of study co-author Martin Cohn.
First Proof That Hormones Affect Finger Length
Scientists had already suspected that sex hormones played a part in finger length, but “causality had never been demonstrated—no one had ever tested the hypothesis that these hormones directly cause the digits to grow differently in males and females,” Cohn said.
Zheng and Cohn took two general approaches for their experiments, which are detailed this week in the journal Proceedings of the National Academy of Sciences.
First, they used genetic tools to deactivate cell receptors—molecules that send and receive signals to and from other cells—for testosterone and estrogen in the developing limb buds of mouse embryos. Second, the scientists boosted the hormone levels of pregnant female mice.
The results proved consistent: Male mice that lacked testosterone receptors in the womb were born with shorter, typically feminine digit proportions, or had index digits longer than their ring digits. Male mice without estrogen receptors had longer ring digits.
Female mice that lacked an estrogen receptor were born with longer digits, and those that did not have testosterone had shorter, superfeminine digits.
The team also found that hormones controlled the rate of cell division in a mouse’s developing digits.