Biologists at the University of Florida have found a reason why men's ring fingers are generally longer than their index fingers — and why the reverse usually holds true for women.
The finding could help medical professionals understand the origin of behavior and disease, which may be useful for customizing treatments or assessing risks in context with specific medical conditions.
Writing this week in the Proceedings of the National Academy of Sciences, developmental biologists Martin Cohn, Ph.D., and Zhengui Zheng, Ph.D., of the Howard Hughes Medical Institute and the department of molecular genetics and microbiology at the UF College of Medicine, show that male and female digit proportions are determined by the balance of sex hormones during early embryonic development. Differences in how these hormones activate receptors in males and females affect the growth of specific digits.
The 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.
It has long been suspected that the digit ratio is influenced by sex hormones, but until now direct experimental evidence was lacking.
"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. "In addition to understanding the basis of one of the more bizarre differences between the sexes, it's exciting to think that our fingers can tell us something about the signals that we were exposed to during a short period of our time in the womb. There is growing evidence that a number of adult diseases have fetal origins. With the new data, we've shown that that the digit ratio reflects one's prenatal androgen and estrogen activity, and that could have some explanatory power."
Cohn and Zheng, also members of the UF Genetics Institute, found that the developing digits of male and female mouse embryos are packed with receptors for sex hormones. By following the prenatal development of the limb buds of mice, which have a digit length ratio similar to humans, the scientists controlled the gene signaling effects of androgen — also known as testosterone — and estrogen.
Essentially, more androgen equated to a proportionally longer fourth digit. More estrogen resulted in a feminized appearance. The study uncovered how these hormonal signals govern the rate at which skeletal precursor cells divide, and showed that different finger bones have different levels of sensitivity to androgen and estrogen.
Since Roman times, people have associated the hand's fourth digit with the wearing of rings. In many cultures, a proportionally longer ring finger in men has been taken as a sign of fertility.
"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."
In dozens of papers and two books, including the seminal "Digit Ratio" in 2002, Manning has studied the meaning of the relative lengths of second and fourth digits in humans, known to scientists as the 2D:4D ratio.
"When Zheng and Cohn blocked testosterone receptors, they got a female digit ratio," Manning said. "When they added testosterone they got super male ratios, and when they added estrogen, super female ratios. And they've provided us with a list of 19 genes that are sensitive to prenatal testosterone and prenatal estrogen.
"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."
Cohn, whose uses the tools of genetics, genomics and molecular biology to study limb development, said his lab began studying the digit ratios after Zheng became determined to find an explanation.
"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 National Institute of Environmental Health Sciences and the Howard Hughes Medical Institute supported this research.
John Pastor | EurekAlert!
Cancer diagnosis: no more needles?
25.05.2018 | Christian-Albrechts-Universität zu Kiel
Less is more? Gene switch for healthy aging found
25.05.2018 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences