New research offers some preliminary evidence that prenatal testosterone exposure is related to women’s emotional control in adulthood. The findings have been published in PLOS One.
Previous research has indicated that the difference between the length of the index finger and the length of the ring finger is an indicator of prenatal testosterone levels. This ratio is known as 2D:4D — or second digit to fourth digit. A low 2D:4D ratio indicates high exposure to testosterone in utero, while a high 2D:4D ratio indicates low exposure.
“We were trying to understand the biological basis of personality. Then, we realized that the 2D:4D ratio is commonly used to indirectly measure prenatal testosterone, a hormone that have been related with several psychological aspects before, and we decided to investigate this association,” explained study author Ángel Rodríguez-Ramos of the University of Córdoba.
In the new study, 101 female college students between 18 and 28 years old completed the Big Five Questionnaire, a common assessment of personality traits. The researchers then compared the participants’ scores on the questionnaire to their 2D:4D ratios.
Rodríguez-Ramos and his colleagues found a positive relationship between 2D:4D ratio and emotional stability. In other words, more emotionally stable participants tended to have higher 2D:4D ratios, indicating lower prenatal testosterone exposure. Less emotionally stable participants, on the other hand, tended to have lower 2D:4D ratios.
“Personality is a complex construct influenced by many genetic and environmental factors, including the ones described in the present article. So, more research is needed in order to completely understand which variables explain personality traits and individual differences in them, and to what extend they do so,” Rodríguez-Ramos told PsyPost.
The researchers also found that higher levels of emotional stability were related to greater life satisfaction and reduced levels of anxiety and depression. “Understanding the factors that influence personality could help to understand the causes of differences in personality and the possible predisposition of certain people to some mental disorders, for this reason we encourage all researchers who are interested in this topic to do research in this field.”
But the researchers found no evidence that prenatal testosterone exposure was related to four other personality dimensions: openness, contentiousness, agreeableness, and extraversion.
The 2D:4D ratio has also become a contentious issue. Scientists haven’t directly confirmed the link between the 2D:4D ratio and prenatal testosterone because they are unable to measure first trimester fetal hormones. Instead, the apparent link is based on a variety of indirect evidence, such as animal models and umbilical cord blood sampling in the second and third trimester.
“It is still unknown how 2D:4D digit ratio is exactly related to prenatal testosterone, so it is really important to understand this association even before carrying out more correlational studies,” Rodríguez-Ramos said.
“Although most of the studies that have investigated the plausible relationship between personality traits and 2D:4D have found interesting associations, many studies have found controversial results, so more investigations should be carried out.”
The study, “Emotional stability is related to 2D:4D and social desirability in women: Possible implications on subjective well-being and psychopathology“, was authored by Ángel Rodríguez-Ramos, Juan Antonio Moriana, Francisco García-Torres, and Manuel Ruiz-Rubio.