A new study suggests that long-distance runners are more attractive because they have greater levels of testosterone which makes them more manly and fertile.

But there are other biological and evolutionary triggers which are constantly drawing us to certain individuals, even if we don’t realise it is happening. Scientists in Geneva discovered that determining whether we are attracted to someone is one of the most complex tasks that the brain undertakes. Here are the scientific secrets of attraction:

Symmetry

Charles Darwin once wrote: "It is certainly not true that there is in the mind of man any universal standards of beauty with respect to the human body."

However recent research suggests that there are universal agreements about beauty which hold true across all cultures and even throughout the animal kingdom.

Probably the most important is facial symmetry. Having a face which is equal on both sides is a biological advert which tells prospective partners that good genes will be found in this body.

Lopsidedness is thought to reflect how development in the womb has been derailed by general poor health, bad DNA, alcohol or tobacco use.