IF ONLY the other halves of the raunchy Christchurch couple had known.

The key to whether or not you’re likely to cheat on your partner could literally be in your hands, with a new study showing the length of a person’s ring finger can be a crucial indicator of how promiscuous they are likely to be.

The study, called Stay or stray? Evidence for alternative mating strategy phenotypes in both men and women was published in Biology Letters this week. It’s based on the fact that rather than being entirely promiscuous or entirely monogamous, humans “invariably” fall somewhere in the middle.

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Using photocopies of the hands of 1,314 British people including 572 men and 742 women, the researchers studied the length of the index finger compared to the ring finger, called the “2D:4D ratio”.

The idea behind it is that the length of someone’s ring finger is an “anatomical marker” of the amount of testosterone they were exposed to in the womb and therefore provides a critical marker for “mating strategy”. Or in other words, how likely or not someone is to cheat.

Generally speaking the longer the ring finger in relation to the index finger, the higher the testosterone the person has been exposed to and the more promiscuous they are likely to be.

The study also found that both males and females have a tendency towards either being promiscuous or monogamous. It’s the first research to show that different mating strategies are used by both sexes rather than being just a male/female distinction.

“While it has been widely suggested that males divide into two mating types (‘cads’ versus ‘dads’) and there is some evidence for a genetic basis for this distinction, this study is the first, to the best of our knowledge, to provide quantitative evidence on their proportional distributions in natural populations,” the authors wrote.

“More importantly, it is the first to suggest that a similar partition may also exist in females.”

Overall, males veered ever-so-slightly towards being promiscuous while females are slightly more reserved.

But before you think your relationship is doomed, the authors were keen to stress that personality type, environmental and cultural factors as well as the type of relationship a person is involved would all play a significant role.