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1 October 2014
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Sex ID

Line angles, finger lengths, and sexual orientation

An image from the Sex ID survey
Sex ID participants were asked to match the slopes of lines.

A person's ability to judge the slope of a line is related to their hand development – specifically, the lengths of certain fingers – as well as their sexual orientation, according to psychologists. Professor Marcia Collaer and colleagues Dr Stian Reimers and Professor John Manning, examined data from the BBC web experiment, Sex ID. Stian Reimers summarises their findings below.

As part of Sex ID, we asked people to match lines that sloped at the same angle, measure the length of their index and ring fingers and indicate their sexual orientation. Here are some of our major findings:

  • Men were better, on average, at matching angles than women.
  • Gay men scored worse than straight men, and lesbians scored better than straight women, on average.
  • The ratio between the length of the index and ring fingers (the 'digit ratio') was associated with ability at the task: The shorter the index finger relative to the ring finger, the better the performance.

Collaer explains: "Although men and women do not differ in overall intelligence, men tend to be better than women, on average, at a few tasks that require spatial judgment. Our research suggests that early exposure to hormones, such as testosterone, in the womb may contribute to this difference. However, it is also important to mention that some women did extremely well on the task – we found that many women earned perfect scores – and some men scored quite badly."

Manning adds: "Finger ratios are thought to be affected by the amount of testosterone we were exposed to in the womb. Higher levels of testosterone are associated with a shorter index finger relative to the ring finger. Some researchers also think that a person's sexual orientation may be influenced by these early hormones."

Collaer: "Higher or lower testosterone levels may encourage certain brain regions to develop in slightly different fashions. However, lots of other factors, including social ones like encouragement and practice, are likely to be as important as hormones – perhaps even more important – in developing a person’s specific thinking abilities."

Marcia Collaer is Associate Professor of Psychology and Neuroscience at Middlebury College, Vermont, and specialises in cognitive and hormonal aspects of sex differences.

Stian Reimers is a researcher at University College London, who worked with the BBC to set up the study.

John Manning is Professor of Psychology at the University of Central Lancashire, and specialises in digit ratios and associated performance.

Read more aricles about the Sex ID results

Take the Sex ID test

Read about the Sex ID experiment

Sex ID frequently asked questions

Other Sex ID articles:

Brain sex
Spatial tests
Handedness
Facial attractiveness
Empathising and systemising

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