For quite a few years researchers have assumed that finger length development and the 2D:4D digit ratio is directed by sex hormones. Nevertheless, until now direct experimental evidence was lacking. However, researchers from Florida have reported an important discovery. They discovered via a study of the limb buds in mice – which are known for having a digit length ratio similar to humans – that human fingers are likely to have likewise sex hormone receptors as seen in the paws of mice.

 A few comments made by researchers Martin Cohn (one of the researchers from Florida) and ‘finger professor’ John Manning:

“The discovery that growth of the developing digits is controlled directly by androgen and estrogen receptor activity confirms that finger proportions are a lifelong signature of our early hormonal milieu,” Cohn said.
“I’ve been struggling to understand this trait since 1998,”said John T. Manning, Ph.D., a professor at Swansea University in the United Kingdom, who was not involved in the current research.“”When I read this study, I thought, thank goodness, we’ve attracted the attention of a developmental biologist with all the sophisticated techniques of molecular genetics and biology.” “When Zheng and Cohn blocked testosterone receptors, they got a female digit ratio,” Manning said. “I find this completely convincing and very useful,” Manning said.“We can now be more focused in our examination of the links between digit ratio and sex-dependent behaviors, diseases of the immune system, cardiovascular disorders and a number of cancers.” “He suggested that the 2D:4D ratio would be an interesting question, and I have to admit to being skeptical,” Cohn said. “When he came back with the initial results, I was blown away. We looked at each others hands, then got busy planning the next experiment.”

The new discovery provides a genetic explanation for a raft of studies that link finger proportions with traits ranging from sperm counts, aggression, musical ability, sexual orientation and sports prowess, to health problems such as autism, depression, heart attack and breast cancer.

The report about the new study appears in this week’s Proceedings of the National Academy of Sciences.

An overview of some key-reports about finger ratios:

Internet study confirms: finger length is linked with handedness!

Handedness & your finger length ratio

While a few years ago early studies had identified a link between various hand characteristics and handness, last year the link was ‘officially’ confirmed in an Australian study that had used a new method for measuring finger length ratio. Now a new BBC internet study by the ‘finger professor’ John T. Manning has confirmed the earlier findings.


Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study.


“The ratio of the length of the second to the fourth digit (2D:4D) may be negatively correlated with prenatal testosterone. Hand preference has been linked with prenatal testosterone and 2D:4D. Here we show that 2D:4D is associated with hand preference for writing in a large internet sample (n>170,000) in which participants self-reported their finger lengths.”

“We replicated a significant association between right 2D:4D and writing hand preference (low right 2D:4D associated with left hand preference) as well as a significant correlation between writing hand preference and the difference between left and right 2D:4D or Dr-l (low Dr-l associated with left hand preference).”

“A new significant correlation between left 2D:4D and writing hand preference was also shown (high left 2D:4D associated with left hand preference). There was a clear interaction between writing hand preference and 2D:4D: The left 2D:4D was significantly larger than the right 2D:4D in male and female left-handed writers, and the right hand 2D:4D was significantly larger than the left hand 2D:4D in male and female right-handed writers.”


The origins of handedness
Your fingers reveal so much about you
The finger book – BOOK
Your left handed child – BOOK

What your hands reveal, what your eye may not see!

Emma Nelson

Emma Nelson studies

‘Digit ratio’ in non-human primates:

‘Digit ratio’ research is not limited to the human hand. Emma Nelson from Department of Archaeology, University of Liverpool is one of the key-researchers who studies ‘digit ratio’ in the hands of primates.

The major focuss in Emma Nelson’s ”digit ratio’ research in primates is:

“Using digit ratios (2D:4D) to investigate social systems in anthropoids; implications for the study of the evolution of hominin sociality.”.

Variation in non-human primate 2D:4D is currently unknown. One of the aims of this project is to map differences in mean 2D:4D within and between non-human primates species.

Digit ratio in non-human primates