London - Women with long index fingers on their left hands are more likely to cheat, say scientists.
A longer index finger – relative to ring finger – has also been linked to exposure to higher levels of female sex hormone oestrogen in the womb.
The findings have surprised scientists as having a longer index finger is associated with having more typical female characteristics.
It had been assumed that more "feminised" women would be less impulsive and more satisfied in their relationships.
But the research, carried out by Eiluned Pearce of Oxford University, found women with higher "left hand digit ratios" were less likely to view their relationships favourably.
The author said these women are likely to be more "feminised" and more sought-after by men. Because they may have more options, this can lead to affairs.
By contrast, being exposed to more of the male sex hormone testosterone in the womb has a more "masculinising" effect - and results in a longer ring finger and a shorter index finger.
The Royal Society Journal research involved 274 women having their fingers measured and taking psychological tests.