Have you ever had your palm read? I haven’t; I don’t believe that the lines on my palms can tell me anything whatsoever about who I am or how long I’m going to live. But look down at your hands. There’s something else staring you right in the face that genuinely can tell you about yourself: the relative lengths of your fingers. Seriously.

Is your index finger longer or shorter than your ring finger? And why does it matter? Image credit: Yamashita Yohei via Flickr

Talk to the hand

The art of palm reading has been around for thousands of years. Palmistry began in India and purports to be able to describe your personality on the basis of the lines and marks on your palms. Not only that, but palm readers also claim your palms predict your future, determining such things as how many children you’ll have and how long you’ll live. You won’t be surprised to read I’m a sceptic: there’s zero evidence it works. Despite many claims to the contrary, there’s also no evidence fingerprints reveal our personalities. Does that mean any suggestion our hands contain information about our character and health is dodgy pseudoscience? Not so fast.

Look down at your hands and focus on the relative length of your index and ring fingers. Which is longer? And by how much? If you want to do this properly, use a ruler to measure the length of your index and ring fingers (for consistency, measure your right hand) from the crease where your finger joins your palm to the fingertip. Divide the length of your index finger by the length of your ring finger. That number is your very own personal 2D:4D ratio (D stands for digit). The relatively longer your ring finger, the lower your 2D:4D ratio. On average, men have lower ratios than women – the average for men is around 0.95 and for women, closer to 1. There’s plenty of solid evidence this ratio has a lot to say about you, particularly if you’re male. Sounds crazy, doesn’t it?

The long and the short of it

Among men, the 2D:4D ratio has been linked to everything from appearance and personality to probability of risk-taking, success on the sports field and proneness to disease. For a start, men with relatively longer ring fingers (a lower 2D:4D ratio) tend to be better at sport and are considered more attractive by women. These men are also considered to be more physically aggressive. A study of male stock market traders found that those with relatively longer ring fingers made more money, took more risks, were more vigilant, had quicker reaction times and stayed in the job longer. Men with a lower 2D:4D ratio have more children and in case you’re wondering, yes, a man with a relatively longer ring finger is also likely to have a relatively longer penis.

A man with a relatively longer index finger (higher 2D:4D ratio) is more likely to have schizophrenia and suffer early heart disease. But he is less likely to be diagnosed with prostate cancer and is also less likely to have autism. There is also evidence for a link between digit ratio and sexual orientation: homosexual and bisexual men tend to have a higher 2D:4D ratio than heterosexual men.

Does the 2D:4D ratio have anything to say about women? As with men, there’s evidence that females with relatively longer ring fingers have more athletic ability. These women also tend to have a better sense of direction than women with relatively longer index fingers and are also more likely to consider themselves assertive and competitive. Similarly, feminist activists are also more likely to have relatively longer ring fingers.

Blame it on testosterone

How on earth does this work? It turns out to be quite simple. The relative lengths of your index and ring fingers are controlled by your exposure to sex hormones not long after you were conceived. Relatively longer fourth digit (low 2D:4D ratio) indicates higher exposure to testosterone while still in the womb, whereas a longer index finger (high 2D:4D ratio) indicates higher exposure to oestrogen. To the best of our understanding, your relative finger lengths are a signature of the hormones you were exposed to during this window of development, about eight to fourteen weeks after you were conceived. A longer ring finger says ‘testosterone was here’. And, importantly, this digit ratio is pretty much set before birth and doesn’t change during puberty.

The key to understanding the digit ratio is that it wasn’t only your fingers developing during this period; so was your brain. Exposure to testosterone at this time promotes growth of the right side of your brain. It is clear that hormone exposure in the womb fixes aspects of your personality well before you were even born. So what are you waiting for? Grab a ruler and work out your 2D:4D ratio.

Links and stuff

• New Scientist Video: what does the length of your fingers say about you?
• Long ring fingers are attached to good-looking guys
• National Geographic: why most men’s ring fingers are so long
• Were the first artists mostly women?