The length of a man's fingers can reveal how physically aggressive he is, Canadian scientists have said.
Finger length is linked to testosterone exposure in the womb
The shorter the index finger is compared to the ring finger, the more boisterous he will be, University of Alberta researchers said.
But the same was not true for verbal aggression or hostile behaviours, they told the journal Biological Psychology after studying 300 people's fingers.
The trend is thought to be linked to testosterone exposure in the womb.
It has been known for some time that there is a direct correlation between finger lengths and the amount of the male sex hormone testosterone that a baby is exposed to in the womb.
In women, the two fingers are usually almost equal in length, as measured from the crease nearest the palm to the fingertip. In men, the ring finger tends to be much longer than the index.
Other studies looking at finger length ratio have suggested that, in men, a long ring finger and symmetrical hands are an indication of fertility, and that women are more likely to be fertile if they have a longer index finger.
One study found boys with shorter ring fingers tended to be at greatest risk of a heart attack in early adulthood, which was linked to testosterone levels.
In the current study, Dr Peter Hurd and his student Allison Bailey measured the fingers of 300 undergraduates at their university.
Men with the shortest index fingers scored higher on measures of physical aggression than those with longer index fingers, but the study's findings did not apply to women.
Dr Hurd is now looking at male hockey players to see whether there is any correlation between finger lengths and each player's penalty record for contact and fouling during matches.
Window to the soul?
He has also been looking at whether men with more feminine finger lengths might be more prone to depression.
He said: "Finger length can tell you a little bit about where personality comes from.
"A large part of our personalities and our traits are determined while we are still in the womb."
But he said finger length should not be used to draw too many conclusions about an individual person.
"For example, you wouldn't want to screen people for certain jobs based on their finger lengths."
Professor John Manning from the University of Central Lancashire's department of psychology, who first realised that sex hormone exposure in the womb influences finger length, agreed.
He said certain individual characteristics correlate better with finger length than others.
"For example, if you had a group of runners and they were about to start a race I could predict reasonably well who was going to win based on their finger length.
"But I would not be able to predict whether someone was neurotic or not."
He said Dr Hurd's findings were logical based on what we know about finger length, testosterone exposure and aggression, but said more research was needed to confirm the findings.
He said another recent study had found women exposed to higher levels of testosterone in the womb, and hence a more 'male' pattern of finger length, displayed more frustrated behaviour when answering challenging telephone calls than other women.